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A Parametric Study of Prefrontal Cortex Involvement in Human Working Memory
Abstract
Although recent neuroimaging studies suggest that prefrontal cortex (PFC) is involved in working memory (WM), the relationship between PFC activity and memory load has not yet been well-described in humans. Here we use functional magnetic resonance imaging (fMRI) to probe PFC activity during a sequential letter task in which memory load was varied in an incremental fashion. In all nine subjects studied, dorsolateral and left inferior regions of PFC were identified that exhibited a linear relationship between activity and WM load. Furthermore, these same regions were independently identified through direct correlations of the fMRI signal with a behavioral measure that indexes WM function during task performance. A second experiment, using whole-brain imaging techniques, both replicated these findings and identified additional brain regions showing a linear relationship with load, suggesting a distributed circuit that participates with PFC in subserving WM. Taken together, these results provide a "dose-response curve" describing the involvement of both PFC and related brain regions in WM function, and highlight the benefits of using graded, parametric designs in neuroimaging research.
... 100 subjects completed the experiment online through Amazon Mechanical Turk. Subjects completed 32 task rounds and performed four different tasks in random order: an attentional vigilance task (1-detect), a vigilance task requiring more WM maintenance (3-detect), and the 1-and 2-back WM task [19,31]. Every task involved monitoring the screen in order to make button presses in response to semi-infrequent target stimuli. ...
... This work directly quantifies the costs associated with the cognitive operations required in working memory and attention tasks, not just how subjects avoid or approach each task. The N-back, a classic WM task, is useful in the study of working memory because it requires the use of many diverse WM operations [31]. Here, we reveal that the N-back's strength may also be its weakness, in that the number of WM operations required to complete it is also what makes it so aversive [43]. ...
... The experiment was coded using a pre-built Javascript framework for online Psychology experiments (JsPsych; [54]) and custom Javascript functions. Subjects were introduced to 4 tasks, each of which was associated with a fractal image (a "task label"; see Fig 1): the 1-and 2-back working memory tasks, and two types of attentional vigilance task, which we refer to as the 1-detect (the default task) and 3-detect [4,5,19,31]. The task label image was presented during the initial task instructions along with the following text: "This picture will always be associated with the following task, like a picture label." ...
Some aspects of cognition are more taxing than others. Accordingly, many people will avoid cognitively demanding tasks in favor of simpler alternatives. Which components of these tasks are costly, and how much, remains unknown. Here, we use a novel task design in which subjects request wages for completing cognitive tasks and a computational modeling procedure that decomposes their wages into the costs driving them. Using working memory as a test case, our approach revealed that gating new information into memory and protecting against interference are costly. Critically, other factors, like memory load, appeared less costly. Other key factors which may drive effort costs, such as error avoidance, had minimal influence on wage requests. Our approach is sensitive to individual differences, and could be used in psychiatric populations to understand the true underlying nature of apparent cognitive deficits.
... Effort may facilitate WM performance through an increased recruitment of neural resources and/or the gain of neural activity. Indeed, previous work has demonstrated increased fMRI activity in prefrontal cortex as WM load increases 22,23 , and we suggest this increase could have been mediated in part by increased effort. ...
... To test this hypothesis, we measured fMRI activity from 12 humans performing a visuospatial WM task that varied the effort required for success. As predicted and consistent with past work, we found that cognitive effort was associated with increased pupil size 24,25 , response times [26][27][28][29] , and amplitudes of delay period activity in frontal and parietal cortex 22,30 . Critically, using Bayesian decoding 31,32 we found that WM representations decoded from early visual cortex were more accurate on more effortful 3 trials. ...
... Effort had the largest effects on the gain of persistent activity in frontal and parietal cortical regions, and little effect in early visual cortex. Increasing memory load, which presumably increases not only difficulty but also effort, also had its greatest effects on BOLD activity in frontal cortex 21,22,30 . Intriguingly, increases in the gain of persistent activity were not restricted to the voxels whose receptive fields contained the memorized target. ...
The neural mechanisms by which motivational factors influence cognition remain unknown. Using fMRI, we tested how cognitive effort impacts working memory (WM). Participants were precued whether WM difficulty would be hard or easy. Hard trials demanded more effort as a later decision required finer mnemonic precision. Behaviorally, pupil size was larger and response times were slower on hard trials suggesting our manipulation of effort succeeded. Neurally, we observed robust persistent activity in prefrontal cortex, especially during hard trials. We found strong decoding of location in visual cortex, where accuracy was higher on hard trials. Connecting these across-region effects, we found that the amplitude of delay period activity in frontal cortex predicted decoded accuracy in visual cortex on a trial-wise basis. We conclude that the gain of persistent activity in frontal cortex may be the source of effort-related feedback signals that improve the quality of WM representations stored in visual cortex.
... In order to assess EF, we used a 3-back working memory task. This task is considered as a canonical EF task, and it is often used to probe individual differences in EF 32,62,63 and often thought to tap the updating subprocess of executive control 64 . In this task, participants were shown on computer screen sequences of digits displayed one at a time. ...
... Since the first three trials were always non-target trials (these three digits did not have "the one displayed three digits ago"), we counted the numbers of hits and correct rejections out of only 24 trials in each block and computed d' 32,66 . Consistent with previous research, one third of the 24 trials were target trials 62 . Compared to the samples usually tested in cognitive psychology studies, our sample was unfamiliar with psychological testing. ...
Belonging to multiple groups is an important feature of our social lives. However, it is largely unknown if it is related to individual differences in cognitive performance. Given that changing self-identities linked to each group requires cognitive operations on knowledge bases associated with each group, the extent to which people belong to multiple groups may be related to individual differences in cognitive performance. Therefore, the main objective of this study was to test if multiple group membership is related to executive function task performance. A socioeconomically diverse sample of 395 individuals in Indonesia participated in this study. Our results show that multiple group membership was positively related to the 3-back working memory performance. However, we also found that this relationship was significant only among participants with high (not median or low) SES. We also observed that Contact diversity was negatively related to working memory performance among participants with low SES. Our results show that the complexity of our social lives is related to individual differences in executive function performance, although this seems to be constrained by SES.
... The orbitofrontal cortex (OFC) is considered a critical part of the olfactory cortex because odor stimulus information ows from the nasal cavity to the olfactory bulb, then passes through the primary olfactory cortex (and areas such as the amygdala), and nally into the secondary olfactory cortex (which includes the OFC) (Mai and Paxinos, 2011). Several previous studies using neuroimaging technique have examined the OFC to study how the olfactory system in the brain functions when an odor stimulus is presented (Cecchetto et (Bonelli & Cummings, 2007;Braver et al., 1997;Rugg& Wilding, 2000), and the FPA has a vital function to support complicated cognitive processes, such as multitasking, high-level goal maintenance, and social cognition (Burgess et al., 2007). ...
... Previous studies have indicated that the DLPFC plays an important role in cognitive control and emotional regulation. This brain region has been associated with working memory (Braver et al., 1997) and episodic memory retrieval (Buckner et al., 1999;Rugg& Wilding, 2000;Wagner, et al., 1998) as well as with goal setting, plan monitoring, modulating anticipation, and using feedback in task performance (Bonelli & Cummings, 2007). Moreover, the DLPFC actively participates in the regulation of emotion (Berlim et al., 2013). ...
Background
Olfactory deterioration is suggested to be a predictor of some neurodegenerative diseases.
Methodology
: Our study compared the functional connectivity between the olfactory cortex and the prefrontal cortex in healthy individuals who exercised regularly and healthy persons who did not. We also assessed their odor threshold. Participants were aged 55 years or older, and the two groups were balanced for age, sex, body mass index, and educational level.
Results
We found that compared with individuals who did not exercise, exercisers had a significantly lower threshold for detecting odors. In addition, the olfactory cortex had stronger connectivity with the PFC in exercisers than in non-exercisers. More specifically, when the PFC was grouped into three subregions, namely, the ventrolateral prefrontal cortex (VLPFC), dorsolateral prefrontal cortex (DLPFC), and frontopolar cortex (FPA), Pearson correlation analysis revealed stronger connectivity between the VLPFC and the OFC, between the OFC and the FPA, and between the left and right OFC hemispheres in the exercisers. In addition, Granger causality indicated higher directional connectivity from the DLPFC to the OFC in exercisers than in non-exercisers.
Conclusion
Our findings indicate that the exercise group not only had better olfactory performance but also had stronger functional connectivity between the olfactory cortex and the PFC than non-exercise group.
... N-back consistently activates various brain regions (Mencarelli et al., 2019;Rottschy et al., 2012;Yaple et al., 2019), particularly bilateral frontal and parietal cortical areas, which are considered essential for working memory (Owen et al., 2005;Rottschy et al., 2012). Brain processing varies with the difficulty of the n-back task, as evidenced by increased amplitudes of evoked fMRI BOLD responses in frontal and parietal cortical regions as load (i.e., n) increases from 1 to 3 back (e.g., Braver et al., 1997), whereas a plateau has been found from 3 to 6 back (Lamichhane et al., 2020). Maturation of frontoparietal systems contributes to WM improvements during childhood and adolescence (e.g., Casey et al., 2005;Kwon et al., 2002;Tamnes et al., 2013;Rosenberg et al., 2020). ...
... At high pág. 122 concentrations, it can induce states of rumination, a frequent component of introversion, by intensifying reflection on internal thoughts and emotions (Braver et al., 2001). ...
This scholarly investigation delves into the neurological interplay between enhanced intellectual engagement and social interaction preferences, focusing on the critical role of specific brain regions and neurotransmitter modulation. Activation patterns in the hippocampus and the prefrontal cortex, particularly influenced by neurotransmitters such as dopamine and serotonin, are explored in relation to their impact on memory enhancement and social motivation. Elevated activity in these brain areas can enhance retention of intellectually stimulating stimuli, potentially fostering social isolation. This research elucidates the neurochemical variations that influence social engagement capacities and clarifies the underlying biological mechanisms predisposing highly intellectual individuals to favor isolation over less stimulating social interactions. This study aims to deepen the understanding of how neuroanatomical and neurochemical dynamics shape introverted behaviors and preference for solitary activities, thereby influencing social integration processes.
... Research into the neural correlates of human working memory (WM) in health and disease has been a major focus of functional Magnetic Resonance Imaging (fMRI) studies since the technique was pioneered in the 1990s (1)(2)(3). Deficits in WM are a hallmark of many neurological and psychiatric diseases, and understanding the neural mechanisms of these impairments is critical for the development of novel treatments and diagnostics. The field of psychiatry has thus embraced the study of WM in psychiatric patients, perhaps most notably in patients with schizophrenia. ...
Background
In studying the neural correlates of working memory (WM) ability via functional magnetic resonance imaging (fMRI) in health and disease, it is relatively uncommon for investigators to report associations between brain activation and measures of task performance. Additionally, how the choice of WM task impacts observed activation-performance relationships is poorly understood. We sought to illustrate the impact of WM task on brain-behavior correlations using two large, publicly available datasets.
Methods
We conducted between-participants analyses of task-based fMRI data from two publicly available datasets: the Human Connectome Project (HCP; n = 866) and the Queensland Twin Imaging (QTIM) Study (n = 459). Participants performed two distinct variations of the n-back WM task with different stimuli, timings, and response paradigms. Associations between brain activation ([2-back − 0-back] contrast) and task performance (2-back % correct) were investigated separately in each dataset, as well as across datasets, within the dorsolateral prefrontal cortex (dlPFC), medial prefrontal cortex, and whole cortex.
Results
Global patterns of activation to task were similar in both datasets. However, opposite associations between activation and task performance were observed in bilateral pre-supplementary motor area and left middle frontal gyrus. Within the dlPFC, HCP participants exhibited a significantly greater activation-performance relationship in bilateral middle frontal gyrus relative to QTIM Study participants.
Conclusions
The observation of diverging activation-performance relationships between two large datasets performing variations of the n-back task serves as a critical reminder for investigators to exercise caution when selecting WM tasks and interpreting neural activation in response to a WM task.
... The classical n-back task mainly involves activation of the dorsolateral and ventrolateral PFC, posterior parietal cortex and motor regions (Owen et al., 2005). An advantage of the n-back task is the possibility to increase working memory load in a stepwise and incremental fashion (Braver et al., 1997), which is usually accompanied by a monotonous decrease in performance (Bopp & Verhaeghen, 2020). This allows for a quantifiable increase in task difficulty. ...
Assessing the pilot’s cognitive state is of increasing importance in aviation, especially for the development of adaptive assistance systems. For this purpose, the assessment of mental workload (MWL) is of special interest as an indication when and how to adapt the automation to fit the pilot’s current needs. Thus, there is a need to assess the pilot continuously, objectively and non-intrusively. Neurophysiological measurements like electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) are promising candidates for such an assessment. Yet, there is evidence that EEG- and fNIRS-based MWL measures are susceptible to influences from other concepts like mental fatigue (MF), and decrease in accuracy when MWL and MF confound. Still, there are only few studies targeting this problem, and no systematic investigation into this problem has taken place. Thus, the validity of neurophysiological MWL measures is not clear yet. In order to undertake such a systematic investigation, I conducted three studies: one experiment in which I investigated the effects of increasing MWL on cortical activation when MF is controlled for; a second experiment in which I examined the effects of increasing MF on cortical activation when MWL is controlled for; and a further comparative analysis of the gathered data. In order to induce MWL and MF in a controllable and comparable fashion, I conceived and used a simplified simulated flight task with an incorporated adapted n-back and monitoring task. I used a concurrent EEG-fNIRS measurement to gain neurophysiological data, and collected performance data and self-reported MWL and MF. In the first study (N = 35), I induce different four levels of MWL by increasing the difficulty of the n-back task, and controlled for MF by means of randomization and a short task duration (≤ 45 minutes). Higher task difficulty elicited higher subjective MWL ratings, declining performance, increased frontal theta band power and decreased frontal deoxyhaemoglobin (HbR) concentration. Furthermore, fNIRS proved more sensitive to tasks with low difficulty, and EEG to tasks with high difficulty. Only the combination of both methods was able to discriminate all four induced MWL levels. Thus, frontal theta band power and HbR were sensitive to changing MWL. In the second study (N = 31), I. I induced MF by means of time on task. Thus, I prolonged the task duration to approx. 90 minutes, and controlled for MWL by using a low but constant task difficulty derived from the first experiment. Over the course of the experiment, the participants’ subjective MF increased linearly, but their performance remained stable. In the EEG data, there was an early increase and levelling in parietal alpha band power and a slower, but steady increase in frontal theta band power. The fNIRS data did not show a consistent trend in any direction with increasing MF. Thus, only parietal alpha and frontal theta band power were sensitive to changing MF. In the third study, I investigated the validity of two EEG indices commonly used for MWL assessment, the Task Load Index (TLI) and the Engagement Index (EI). I computed the indices from the data of the two experiments, and compared the results between the datasets, and to single band powers. The TLI increased with increasing MWL, but was less sensitive than theta band power alone, and varied slightly with increasing MF. The EI did not vary with MWL, and was not sensitive to gradually increasing MF. Thus, neither index could be considered a valid MWL measure. In sum, neurophysiological measures can be used to assess changes in MWL. Yet, frontal HbR was the only measure sensitive to MWL that did not also vary with MF, and further research is needed to conclude if this finding holds true under different task characteristics. Thus, the tested EEG and fNIRS measures are only valid indications of MWL when confounding effects of MF are explicitly controlled for. I discuss further influences on the tested EEG and fNIRS measures, possible combinations with other data sources, and practical challenges for a neurophysiological MWL assessment. I conclude that neurophysiological measures should be used carefully outside the laboratory, as their validity will likely suffer in realistic settings. When their limitations are understood and respected, they can help to understand the cognitive processes involved in MWL, and can be a valuable addition to an MWL assessment.
... On the other hand, the right precentral gyrus has been associated with motor processes [72,74], while the right superior frontal gyrus has been reported to be involved in motor control tasks [73,75]. Moreover, parts of this region appear to support working memory [76,77] and to be anatomically connected with the DMN [78][79][80], placing its function between the temporal pole and the precentral gyrus. Increased functional connectivity between the MPFC, which is responsible for action and behavior regulation [81], and distant brain regions may represent a neural correlate of the complex sensory, motor and cognitive integration processes associated with playing a musical instrument. ...
Background
Participation in multimodal leisure activities, such as playing a musical instrument, may be protective against brain aging and dementia in older adults (OA). Potential neuroprotective correlates underlying musical activity remain unclear.
Objective
This cross-sectional study investigated the association between lifetime musical activity and resting-state functional connectivity (RSFC) in three higher-order brain networks: the Default Mode, Fronto-Parietal, and Salience networks.
Methods
We assessed 130 cognitively unimpaired participants (≥ 60 years) from the baseline cohort of the DZNE-Longitudinal Cognitive Impairment and Dementia Study (DELCODE) study. Lifetime musical activity was operationalized by the self-reported participation in musical instrument playing across early, middle, and late life stages using the Lifetime of Experiences Questionnaire (LEQ). Participants who reported musical activity during all life stages ( n = 65) were compared to controls who were matched on demographic and reserve characteristics (including education, intelligence, socioeconomic status, self-reported physical activity, age, and sex) and never played a musical instrument ( n = 65) in local (seed-to-voxel) and global (within-network and between-network) RSFC patterns using pre-specified network seeds.
Results
Older participants with lifetime musical activity showed significantly higher local RSFC between the medial prefrontal cortex (Default Mode Network seed) and temporal as well as frontal regions, namely the right temporal pole and the right precentral gyrus extending into the superior frontal gyrus, compared to matched controls. There were no significant group differences in global RSFC within or between the three networks.
Conclusion
We show that playing a musical instrument during life relates to higher RSFC of the medial prefrontal cortex with distant brain regions involved in higher-order cognitive and motor processes. Preserved or enhanced functional connectivity could potentially contribute to better brain health and resilience in OA with a history in musical activity.
Trial registration
German Clinical Trials Register ( DRKS00007966 , 04/05/2015).
... This pattern would be ascribed to failures of attentional control in optimally maintaining the task goal for trials with slower responses (e.g., De Jong et al., 1999;San José et al., 2021;Scaltritti et al., 2015), possibly because, in these slower trials, control may be more frequently reactive rather than proactive. In the dual-task procedure, because of the working memory load induced by the n-back task (Braver et al., 1997;Owen et al., 2005), there should be fewer resources available to apply proactive control consistently across the whole experiment, with a subsequent increased reliance on reactive control. Therefore, the semantic Stroop effect may also surface in faster responses (although those responses would likely be slower than the fastest responses in the single-task procedure due to concurrent-task costs; e.g., de Fockert et al., 2001). ...
We investigated whether, during visual word recognition, semantic processing is modulated by attentional control mechanisms directed at matching semantic information with task-relevant goals. In previous research, we analyzed the semantic Stroop interference as a function of response latency (delta-plot analyses) and found that this phenomenon mainly occurs in the slowest responses. Here, we investigated whether this pattern is due to reduced ability to proactively maintain the task goal in these slowest trials. In two pairs of experiments, participants completed two semantic Stroop tasks: a classic semantic Stroop task (Experiment 1A and 2A) and a semantic Stroop task combined with an n -back task (Experiment 1B and 2B). The two pairs of experiments only differed in the trial pace, which was slightly faster in Experiments 2A and 2B than in Experiments 1A and 1B. By taxing the executive control system, the n -back task was expected to hinder proactive control. Delta-plot analyses of the semantic Stroop task replicated the enhanced effect in the slowest responses, but only under sufficient time pressure. Combining the semantic Stroop task with the n -back task produced a change in the distributional profile of semantic Stroop interference, which we ascribe to a general difficulty in the use of proactive control. Our findings suggest that semantic Stroop interference is, to some extent, dependent on the available executive resources, while also being sensitive to subtle variations in task conditions.
... The high-demand task involved identical stimuli and timing (including the tone accompanying children's faces) but called for a button press when any face matched the one presented three steps earlier (also 20% of all trials). Note that this task involves the active maintenance and updating of humans' faces in working memory and therefore requires cognitive control (Braver et al., 1997). ...
Daily life frequently offers a choice between activities that are profitable but mentally demanding (cognitive labor) and activities that are undemanding but also unproductive (cognitive leisure). Although such decisions are often implicit, they help determine academic performance, career trajectories, and even health outcomes. Previous research has shed light both on the executive control functions that ultimately define cognitive labor and on a “default mode” of brain function that accompanies cognitive leisure. However, little is known about how labor/leisure decisions are actually made. Here, we identify a central principle guiding such decisions. Results from 3 economic-choice experiments indicate that the motivation underlying cognitive labor/leisure decision making is to strike an optimal balance between income and leisure, as given by a joint utility function. The results reported establish a new connection between microeconomics and research on executive function. They also suggest a new interpretation of so-called ego-depletion effects and a potential new approach to such phenomena as mind wandering and self-control failure.
... This initial result reaffirms prior work that has demonstrated the effects of temporal distinctiveness on memory retrieval (Brown et al., 2007), here using a formally simple mechanism for temporal encoding that is consistent in its properties with previous implementations (Manning et al., 2014). We show that this mechanism, coupled with a neural network mechanism trained to evaluate the temporal "distance" between stimuli, can reproduce empirically observed patterns of performance in the N-back task (Braver et al., 1997;M. J. Kane et al., 2007). ...
The N-back task is often considered to be a canonical example of a task that relies on working memory (WM), requiring both maintenance of representations of previously presented stimuli and also processing of these representations. In particular, the set-size effect in this task (e.g., poorer performance on three-back than two-back judgments), as in others, is often interpreted as indicating that the task relies on retention and processing of information in a limited-capacity WM system. Here, we consider an alternative possibility: that retention in episodic memory (EM) rather than WM can account for both set-size and lure effects in the N-back task. Accordingly, performance in the N-back task may reflect engagement of the processing (“working”) function of WM but not necessarily limits in either that processing ability nor in retention (“memory”). To demonstrate this point, we constructed a neural network model that was augmented with an EM component, but lacked any capacity to retain information across trials in WM, and trained it to perform the N-back task. We show that this model can account for the set-size and lure effects obtained in an N-back study by M. J. Kane et al. (2007), and that it does so as a result of the well-understood effects of temporal distinctiveness on EM retrieval, and the processing of this information in WM. These findings help illuminate the ways in which WM may interact with EM in the service of cognitive function and add to a growing body of evidence that tasks commonly assumed to rely on WM may alternatively (or additionally) rely on EM.
... This prediction was motivated by the cognitive control literature, in which performance monitoring typically entails the presence of a representation of past events and signals that indicate that additional effort is needed in cases of suboptimal performance (29)(30)(31)(32). In the case of cognitive foraging, we hypothesized that increasing neural activation during each within-patch search could represent increases in working memory load and/or signals indicating a failure to generate the next unique similar response with the expected speed and ease, which ultimately triggers a switch to a new patch (33)(34)(35)(36)(37). ...
Humans may retrieve words from memory by exploring and exploiting in “semantic space” similar to how nonhuman animals forage for resources in physical space. This has been studied using the verbal fluency test (VFT), in which participants generate words belonging to a semantic or phonetic category in a limited time. People produce bursts of related items during VFT, referred to as “clustering” and “switching.” The strategic foraging model posits that cognitive search behavior is guided by a monitoring process which detects relevant declines in performance and then triggers the searcher to seek a new patch or cluster in memory after the current patch has been depleted. An alternative body of research proposes that this behavior can be explained by an undirected rather than strategic search process, such as random walks with or without random jumps to new parts of semantic space. This study contributes to this theoretical debate by testing for neural evidence of strategically timed switches during memory search. Thirty participants performed category and letter VFT during functional MRI. Responses were classified as cluster or switch events based on computational metrics of similarity and participant evaluations. Results showed greater hippocampal and posterior cerebellar activation during switching than clustering, even while controlling for interresponse times and linguistic distance. Furthermore, these regions exhibited ramping activity which increased during within-patch search leading up to switches. Findings support the strategic foraging model, clarifying how neural switch processes may guide memory search in a manner akin to foraging in patchy spatial environments.
... Some of them can be easily measured with fNIRS, in particular ones belonging to the ECN (i.e., frontopariteral network). As an illustration, the DLPFC activity increases linearly with working memory load [9], suggesting that it represents a reliable proxy measure of mental workload [45,51]. ...
... WM is a short-term active memory associated with the temporary storage and manipulation of information [19] [21]. It is well known that the prefrontal cortex (PFC) is involved in the processing of WM [22] [23]. ...
Future deep space exploration missions will expose astronauts to various stressors that can impair cognitive abilities and pose a risk to crew mental health and performance. Therefore cognitive assessment strategies are needed. The assessment of cognitive state can be done by monitoring mental effort (amount of effort people have to exert mentally to perform a task). The mental workload construct assumes that task-related brain activity consumes a certain amount of mental resources that is related to the difficulty of the task, and that this resource demand can be quantified and measured. Functional near-infrared spectroscopy (fNIRS) is a non-invasive brain monitoring technology that provides a real-time blood oxygenation measure via optical intensity, thus indicating brain activation. Being easy to use, low cost, and safe for long-term and repeated measurements, fNIRS becomes increasingly important in spaceflight. Our objective is to demonstrate the feasibility of assessing mental workload in an extreme environment by measuring brain oxygenation with a portable fNIRS device (two channels placed on the forehead).Nine subjects were isolated for four days under extreme conditions and temperatures up to-14°C. Subjects were asked to perform a cognitive task known as the n-back task, a continuous performance task commonly used to assess memory processes and mental workload in cognitive neuroscience. Using the portable Hybrid-8 toolkit from Biosignalsplux, two fNIRS sensors have been placed on the left and right prefrontal cortex (PFC) to measure relative concentrations of oxygenated hemoglobin (HbO) during the performance of a n-back task. To obtain baseline measurements of brain activity, subjects performed a resting task (fixation cross task) before and after the n-back task. The protocol was again performed in a non-restrained, comfortable environment to compare the results with the extreme environment. A subsequent analysis of the effects of cognitively demanding tasks on blood oxygenation in the PFC was performed using one-way analysis of variance (ANOVA) and showed statistically significant increase in HbO during the cognitive tasks compared to baseline measurements in both extreme and non-extreme environment. In addition, compared to non-extreme environments, there was a significantly increased resource demand for HbO during cognitively demanding tasks in extreme conditions. This preliminary study shows promising results for measuring brain oxygenation during cognitive task performance under extreme environmental conditions using portable fNIRS.
... Other prefrontal regions are sensitive to patterns [124], consistent with a role in providing context for the type of object observed ("what"). Because activity in prefrontal cortex adapts quickly to task requirements or changes in the environment [125][126][127], it is in position to promote changes in context through its connections with sensory areas. ...
The relationship between brain and consciousness has been debated since Descartes in the 1500s, new theories arising in the twentieth century with the development of modern neuroscience. All are controversial due to the lack of consensus on the definition of consciousness, what cognitive properties must be explained, and how to evaluate sentience. Most theoretical explanations bear little relationship to our inner conscious experiences. In the current monograph, the normal alert state of consciousness is defined, and components to be explained are delineated. Debunking misconceptions from previous theories and presenting new evidence, a model is proposed whereby the hippocampus plays a central role in executing and coordinating cognitive functions associated with normal alert consciousness. Key elements of the model reflect recent findings that the combined effect from the left and right hippocampus influences other regions involved in performing many or all cognitive tasks while filtering out irrelevant information. Methods are described for testing the model. Finally, implications are discussed for a variety of neurological disorders and philosophophical issues, including free will and the possibility of sentience in artificial intelligence.
... Other prefrontal regions are sensitive to patterns [124], consistent with a role in providing context for the type of object observed ("what"). Because activity in prefrontal cortex adapts quickly to task requirements or changes in the environment [125][126][127], it is in position to promote changes in context through its connections with sensory areas. ...
... The n-back task departs from span tasks by allowing working memory assessment under different levels of memory load. Of note, neuroimaging studies of working memory often analyze differences in brain activity between two different loads of the n-back task (e.g., 2-back minus 0-back condition, Braver et al., 1997;Yaple & Arsalidou, 2018); yet, purely behavioral studies rarely apply the subtractions method to analyze n-back task performance (e.g., use of only the 2-back condition, Duan et al., 2010;Waris et al., 2017). ...
The multicomponent nature of executive functions (EF) has long been recognized, pushing for a better understanding of both the commonalities and the diversity between EF components. Despite the advances made, the operationalization of performance in EF tasks remains rather heterogeneous, and the structure of EF as modeled by confirmatory factor analyses (CFA) is still a topic of debate (Karr et al., 2018). The present work demonstrates these two issues are related, showing how different operationalizations in task-based performance indicators impact the resulting models of EF structure with CFA. Using bootstrapped data from 294 children (8–12 years old) and nine EF tasks (tapping inhibition, working memory, and cognitive flexibility), we first show improved model convergence and acceptance when operationalizing EF through single tasks’ scores (e.g., incongruent trials, Flanker task) relative to difference scores (e.g., incongruent minus congruent trials, Flanker task). Furthermore, we show that response times exhibit poor model convergence and acceptance compared not only to accuracy but also drift rate. The latter, a well-known indicator in drift-diffusion models, is found to present the best trade-off between convergence and acceptance to model EF with CFA. Finally, we examine how various operationalizations of performance in EF tasks impact CFA model comparison in the assessment of EF structure and discuss the theoretical foundations for these results.
... For the condition with pre-sleep cognitive activity (i.e., cognitive activity, CA), participants were given a series of cognitive tasks, followed by a 90-minute nap. Specifically, the cognitive tasks included the N-back task [30], the Stroop color-word task [31], the Simon switching task [32], and the word-pair memory task ( [33,34]; Fig. 1b), which respectively activate working memory, inhibitory control, cognitive flexibility, and associative memory function, mimicking real-life situations that often involve multiple cognitive domains. The detailed task description can be found in the supplementary materials. ...
Objectives:
Understanding the influence of cognitive activity on subsequent sleep has both theoretical and applied implications. This study aims to investigate the effect of pre-sleep cognitive activity, in the context of avoiding emotional interference, on macro-sleep and sleep spindles.
Methods:
In a within-subjects design, participants' sleep electroencephalography was collected in both the with and without pre-sleep cognitive activity conditions. Subsequent macro-sleep (i.e., sleep stage distribution and sleep parameters) and spindle characteristics (i.e., density, amplitude, duration, and frequency) were analyzed. In addition, a novel machine learning framework (i.e., deep neural network, DNN) was used to discriminate between cognitive activity and control conditions.
Results:
There were no significant differences in macro-sleep and sleep spindles between the cognitive activity and control conditions. Spindles-based DNN models achieved over 96% accuracy in differentiating between the two conditions, with fast spindles performing better than full-range and slow spindles.
Conclusions:
These results suggest a weak but positive effect of pre-sleep cognitive activity on subsequent sleep. It sheds light on a possible low-cost and easily accessible sleep intervention strategy for clinical and educational purposes.
... The same procedure would be applied for all conditions in which n increases. As n increases, so does the cognitive load with a resulting drop in performance (Braver et al., 1997). The simultaneous dualprocessing requirements of the n-back task meet face validity criteria for assessing working memory, although there is recent divergent evidence that suggests the n-back task weakly correlates with change detection, another working memory task (Frost et al., 2021;Gajewski et al., 2018). ...
... Several neuropsychological and experimental tasks have been developed to evaluate how updating differs from passive short-term storage. The most used tasks involve dynamically monitoring and updating verbal or spatial information, such as in the N-back task (Braver et al., 1997), where the subject is presented with a sequence of stimuli and must decide whether each one is similar to the one presented N trials ago. Another example is the running span task (Morris & Jones, 1990), ...
Duration estimation is a conceptual ability that plays a crucial role in human behavior. Impairments in duration estimation ability have a significant impact on daily autonomy and social and cognitive capacities, even more so in psychological disorders. It has been recently shown that the ability to estimate durations develops at a slower pace in individuals with mild intellectual disability (MID) compared to typically developing (TD) individuals. More generally, it has been also demonstrated that duration estimation requires working memory updating. In the present study, we compared the duration estimation and updating performances of individuals with idiopathic MID without associated disorders aged from 10 to 20 years to those of typical individuals of the same ages (N = 160). Our results highlight a developmental lag not only in the capacity to estimate short durations (< 1 second) in individuals with idiopathic MID, both in a bisection task and in a reproduction task, but also in working memory updating capacity. The findings also emphasize - for the first time - the importance of updating for both the age-related increase in duration estimation capacities and the deficits of these capacities in idiopathic MID. This is consistent with the hypothesis that duration estimation deficits in idiopathic MID may be due, to a large extent, to lower updating abilities.
... We used the n-back task to measure working memory because this task specifically measures the maintenance and selective updating of information in mind (Gajewski et al., 2018;Rac-Lubashevsky & Kessler, 2016). In this task, a series of letters (i.e., A, B, C, D, E, F, G, and H) were presented one by one on the screen (Braver et al., 1997). Participants were asked to memorize the letters and press the space bar when the current letter was the same as the first one (i.e., n = 0) or the one presented n trials ago (e.g., n = 3), as shown in Fig. 3. ...
Background
Coding has become an integral part of STEM education. However, novice learners face difficulties in processing codes within embedded structures (also termed nested structures). This study aimed to investigate the cognitive mechanism underlying the processing of embedded coding structures based on hierarchical complexity theory, which suggests that more complex hierarchies are involved in embedded versus sequential coding structures. Hierarchical processing is expected to place a great load on the working memory system to maintain, update, and manipulate information. We therefore examined the difference in cognitive load induced by embedded versus sequential structures, and the relations between the difference in cognitive load and working memory capacity.
Results
The results of Experiment 1 did not fully support our hypotheses, possibly due to the unexpected use of cognitive strategies and the way stimuli were presented. With these factors well controlled, a new paradigm was designed in Experiment 2. Results indicate that the cognitive load, as measured by the accuracy and response times of a code comprehension task, was greater in embedded versus sequential conditions. Additionally, the extra cognitive load induced by embedded coding structures was significantly related to working memory capacity.
Conclusions
The findings of these analyses suggest that processing embedded coding structures exerts great demands on the working memory system to maintain and manipulate hierarchical information. It is therefore important to provide scaffolding strategies to help novice learners process codes across different hierarchical levels within embedded coding structures.
... A good example is holding two numbers in mind and trying to multiply them mentally. WM also retrieves and uses information from long-term memory, making WM an input/output pathway for the long-term storage sites from a modeling point of view [53][54][55][56][57][58][59]. ...
Brain-computer interfaces (BCI) translate brain signals into artificial output to restore or replace natural central nervous system (CNS) functions. Multiple processes, including sensorimotor integration, decision-making, motor planning, execution, and updating, are involved in any movement. For example, a BCI may be better able to restore naturalistic motor behaviors if it uses signals from multiple brain areas and decodes natural behaviors’ cognitive and motor aspects. This review provides an overview of the preliminary information necessary to plan a BCI project focusing on intracortical implants in primates. Since the brain structure and areas of non-human primates (NHP) are similar to humans, exploring the result of NHP studies will eventually benefit human BCI studies. The different types of BCI systems based on the target cortical area, types of signals, and decoding methods will be discussed. In addition, various successful state-of-the-art cases will be reviewed in more detail, focusing on the general algorithm followed in the real-time system. Finally, an outlook for improving the current BCI research studies will be debated.
... Considerable evidence suggests that RB category learning depends on working memory and selective attention (Ashby, Alfonso-Reese, Turken, & Waldron, 1998;Maddox, Filoteo, Hejl, et al., 2004;Waldron & Ashby, 2001;Zeithamova & Maddox, 2006) -skills that are both thought to depend heavily on prefrontal cortex (PFC; e.g., Braver et al., 1997;Curtis & D'Esposito, 2003;Miller & Cohen, 2001). As a result, models of RB category learning will assign a prominent role to the PFC. ...
The Cambridge Handbook of Computational Cognitive Sciences is a comprehensive reference for this rapidly developing and highly interdisciplinary field. Written with both newcomers and experts in mind, it provides an accessible introduction of paradigms, methodologies, approaches, and models, with ample detail and illustrated by examples. It should appeal to researchers and students working within the computational cognitive sciences, as well as those working in adjacent fields including philosophy, psychology, linguistics, anthropology, education, neuroscience, artificial intelligence, computer science, and more.
... We selected this study for our systems genomics analysis as the phenotypes measured activate specific neuroanatomical networks and are impaired in disorders of neurodevelopmental origin with significant heritability. For example, tasks requiring use of working memory, a type of short-term memory that recruits a cortical-subcortical network including the dorsolateral prefrontal cortex, shows a genetic component in twins, and is impaired in schizophrenia (Braver et al. 1997;Blokland et al. 2008;Minzenberg et al. 2009). With a standardized neurocognitive test battery and genotyping on over 8,000 community youths aged 8-21 years, the PNC is the largest publicly available dataset for genotypephenotype analysis of peri-adolescent cognition (Gur et al. 2014;Satterthwaite et al. 2014;Calkins et al. 2015). ...
An open challenge in human genetics is to better understand the systems-level impact of genotype variation on developmental cognition. To characterize the genetic underpinnings of peri-adolescent cognition, we performed genotype-phenotype and systems analysis for binarized accuracy in nine cognitive tasks from the Philadelphia Neurodevelopmental Cohort (~2,200 individuals of European continental ancestry aged 8-21 years). We report a region of genome-wide significance within the 3' end of the Fibulin-1 gene (P = 4.6 × 10-8), associated with accuracy in nonverbal reasoning, a heritable form of complex reasoning ability. Diffusion tensor imaging data from a subset of these participants identified a significant association of white matter fractional anisotropy with FBLN1 genotypes (P < 0.025); poor performers show an increase in the C and A allele for rs77601382 and rs5765534, respectively, which is associated with increased fractional anisotropy. Integration of published human brain-specific 'omic maps, including single-cell transcriptomes of the developing human brain, shows that FBLN1 demonstrates greatest expression in the fetal brain, as a marker of intermediate progenitor cells, demonstrates negligible expression in the adolescent and adult human brain, and demonstrates increased expression in the brain in schizophrenia. Collectively these findings warrant further study of this gene and genetic locus in cognition, neurodevelopment, and disease. Separately, genotype-pathway analysis identified an enrichment of variants associated with working memory accuracy in pathways related to development and to autonomic nervous system dysfunction. Top-ranking pathway genes include those genetically associated with diseases with working memory deficits, such as schizophrenia and Parkinson's disease. This work advances the "molecules-to-behavior" view of cognition and provides a framework for using systems-level organization of data for other biomedical domains.
... Memory Functioning: Verbal Working Memory -Verbal working memory will be measured using the N-back task (Braver et al., 1997). The n-back task measures verbal working memory. ...
Background
To improve psychological treatments for major depressive disorder (MDD), a better understanding on how symptoms ameliorate during treatment is essential. In cognitive behavioral therapy (CBT), it is unclear whether procedures focused on the acquisition of CBT skills play a causal role in the improvement of CBT skills. In this randomized trial, we isolate a single CBT Skill Acquisition Procedure (CBTSAP) and test its direct effects on CBT skills and related therapy processes (i.e., change in (idiosyncratic) dysfunctional thinking and reward processing). We hypothesize that the CBTSAP causes improvements in CBT skills and related therapy processes compared to an active control condition. In addition, we hypothesize that individual differences in attentional bias and memory functioning (defined as learning capacity) moderate the effects of CBTSAP on outcomes and that using mental imagery as a cognitive support strategy to strengthen the effects of the CBTSAP will be most beneficial for patients with low learning capacity.
Method
150 patients with MDD will be randomized to one of three conditions: 1. an active control condition, 2. CBTSAP, 2. CBTSAP plus mental imagery, all consisting of three sessions. Primary outcomes will be change in CBT skills, changes in (idiosyncratic) dysfunctional thoughts and behaviors, reward processing. Depressive symptoms are a secondary outcome. Measures of learning capacity will be conducted at baseline and tested as a potential moderator.
Discussion
Knowing whether and for whom the acquisition of CBT skills leads to change in therapy processes and a subsequent reduction of depressive symptoms will inform on how to personalize and optimize psychotherapy outcomes for depression.
Trial registration
The trial is registered at the German Clinical Trial Register (DKTR; registration number: DRKS00024116).
... Some of them can be easily measured with fNIRS, in particular ones belonging to the ECN (i.e., frontopariteral network). As an illustration, the DLPFC activity increases linearly with working memory load (Braver et al., 1997), suggesting that it represents a reliable proxy measure of mental workload (Mandrick et al., 2016;Parent et al., 2019). ...
... Two variations of the auditory n-back task, (a) one-back (easy) and (b) three-back (difficult), were modeled after a standard paradigm (Braver et al., 1997) and were used to measure the working memory and executive functions (Jonathan et al., 1997). Both variations contain 72 trials each (24 target trials and 48 nontarget trials). ...
Neuropsychological studies have demonstrated that meningioma patients frequently exhibit cognitive deficits before surgery and show only limited improvement after surgery. Combining neuropsychological with functional imaging measurements can shed more light on the impact of surgery on cognitive brain function. We aimed to evaluate whether surgery affects cognitive brain activity in such a manner that it may mask possible changes in cognitive functioning measured by neuropsychological tests. Twenty‐three meningioma patients participated in a fMRI measurement using a verbal working memory task as well as three neuropsychological tests focused on working memory, just before and 3 months after surgery. A region of interest based fMRI analysis was used to examine cognitive brain activity at these timepoints within the central executive network and default mode network. Neuropsychological assessment showed impaired cognitive functioning before as well as 3 months after surgery. Neuropsychological test scores, in‐scanner task performance as well as brain activity within the central executive and default mode network were not significantly different between both timepoints. Our results indicate that surgery does not significantly affect cognitive brain activity in meningioma patients the first few months after surgery. Therefore, the lack of cognitive improvement after surgery is not likely the result of compensatory processes in the brain. Cognitive deficits that are already present before surgery appear to be persistent after surgery and a considerable recovery period. Our study shows potential leads that comprehensive cognitive evaluation can be of added value so that cognitive functioning may become a more prominent factor in clinical decision making.
Background and Purpose
Preferences can be developed for, or against, specific brands and services. Using two functional magnetic resonance imaging (fMRI) experiments, this study investigated two dissociable aspects of reward processing, craving and liking, in chocolate lovers. The goal was to further delineate the neural basis supporting branding effects using familiar chocolate (FC) and unfamiliar chocolate (UC) brand images.
Methods
In the first experiment, subjects rated their subjective craving and liking on a scale of 1‐5 (weak‐strong) for each FC and UC image. In the second experiment, they performed a choice task between FC and UC images.
Results
Both the craving and liking ratings were significantly greater for FC and were differentially correlated with choice behavior. Craving ratings predicted greater preference for UC, and liking ratings predicted greater preference for FC. A contrast of neural activity for UC versus FC choice trials revealed significantly greater activation for UC choices in the bilateral inferior frontal gyrus and right caudate head. Response times for the FC images were faster than UC images; fMRI activity in the ventromedial prefrontal cortex was significantly correlated with response times during FC trials, but not UC trials. These correlations were significantly different from each other at the group level.
Conclusions
The choices for branded chocolate products are driven by higher subjective reward ratings and lower neural processing demands.
Auditory short-term memory (STM) is a key process in auditory cognition, with evidence for partly distinct networks subtending musical and verbal STM. The delayed matching-to-sample task (DMST) paradigm has been found suitable for comparing musical and verbal STM and for manipulating memory load. In this study, musical and verbal DMSTs were investigated with measures of activity in frontal areas with functional near-infrared spectroscopy (fNIRS): Experiment 1 compared musical and verbal DMSTs with a low-level perception task (that does not entail encoding, retention, or retrieval of information), to identify frontal regions involved in memory processes. Experiment 2 manipulated memory load for musical and verbal materials to uncover frontal brain regions showing parametric changes in activity with load and their potential differences between musical and verbal materials. A FIR model was used to deconvolute fNIRS signals across successive trials without making assumptions with respect to the shape of the hemodynamic response in a DMST. Results revealed the involvement of the dorso-lateral prefrontal cortex (dlPFC) and inferior frontal gyri (IFG), but not of the superior frontal gyri (SFG) in both experiments, in keeping with previously reported neuroimaging data (including fMRI). Experiment 2 demonstrated a parametric variation of activity with memory load in bilateral IFGs during the maintenance period, with opposite directions for musical and verbal materials. Activity in the IFGs increased with memory load for verbal sound sequences, in keeping with previous results with n-back tasks. The decreased activity with memory load observed with musical sequences is discussed in relation to previous research on auditory STM rehearsal strategies. This study highlights fNIRS as a promising tool for investigating musical and verbal STM not only for typical populations, but also for populations with developmental language disorders associated with functional alterations in auditory STM.
The cerebral cortex is populated by specialized regions that are organized into networks. Here we estimated networks from functional MRI (fMRI) data in intensively sampled participants. The procedure was developed in two participants (scanned 31 times) and then prospectively applied to 15 participants (scanned 8-11 times). Analysis of the networks revealed a global organization. Locally organized first-order sensory and motor networks were surrounded by spatially adjacent second-order networks that linked to distant regions. Third-order networks possessed regions distributed widely throughout association cortex. Regions of distinct third-order networks displayed side-by-side juxtapositions with a pattern that repeated across multiple cortical zones. We refer to these as Supra-Areal Association Megaclusters (SAAMs). Within each SAAM, two candidate control regions were adjacent to three separate domain-specialized regions. Response properties were explored with task data. The somatomotor and visual networks responded to body movements and visual stimulation, respectively. Second-order networks responded to transients in an oddball detection task, consistent with a role in orienting to salient events. The third-order networks, including distinct regions within each SAAM, showed two levels of functional specialization. Regions linked to candidate control networks responded to working memory load across multiple stimulus domains. The remaining regions dissociated across language, social, and spatial / episodic processing domains. These results suggest progressively higher-order networks nest outwards from primary sensory and motor cortices. Within the apex zones of association cortex, there is specialization that repeatedly divides domain-flexible from domain-specialized regions. We discuss implications of these findings including how repeating organizational motifs may emerge during development.
The N-back task is widely used to investigate working memory. Previous functional magnetic resonance imaging (fMRI) studies have shown that local brain activation depends on the difficulty of the N-back task. Recently, changes in functional connectivity and local activation during a task, such as a single-hand movement task, have been reported to give the distinct information. However, previous studies have not investigated functional connectivity changes in the entire brain during N-back tasks. In this study, we compared alterations in functional connectivity and local activation related to the difficulty of the N-back task. Because structural connectivity has been reported to be associated with local activation, we also investigated the relationship between structural connectivity and accuracy in a N-back task using diffusion tensor imaging (DTI). Changes in functional connectivity depend on the difficulty of the N-back task in a manner different from local activation, and the 2-back task is the best method for investigating working memory. This indicates that local activation and functional connectivity reflect different neuronal events during the N-back task. The top 10 structural connectivities associated with accuracy in the 2-back task were locally activated during the 2-back task. Therefore, structural connectivity as well as fMRI will be useful for predicting the accuracy of the 2-back task.
The fractal dimension of cognition refers to the idea that the cognitive processes of the human brain exhibit fractal properties. This means that certain patterns of cognitive activity, such as visual perception, memory, language, or problem-solving, can be described using the mathematical concept of fractal dimension.
The idea that cognition is fractal has been proposed by some researchers as a way to understand the complex, self-similar nature of the human brain. However, it’s a relatively new idea and is still under investigation, so it’s not yet clear to what extent cognitive processes exhibit fractal properties or what implications this might have for our understanding of the brain and clinical practice. Indeed, the mission of the “fractal neuroscience” field is to define the characteristics of fractality in human cognition in order to differently characterize the emergence of brain disorders.
Some studies suggest that patients with relapsing-remitting multiple sclerosis have problems in the functioning of working memory, and more specifically in executive functions, but the available results are still inconsistent. The aim of the present study was to examine executive functioning in multiple sclerosis using classical and representative tasks for divided attention, updating, attentional shifting, and inhibition. The sample was composed of 48 participants aged between 18 and 59 years (24 persons living with multiple sclerosis and 24 healthy participants matched in age and education level). The executive functions of divided attention, updating, attentional shifting, and inhibition were analyzed through the Dual-Task Paradigm, the N-Back task, the Trail Making Test (TMT), and the Stroop test, respectively. The analyses of the data showed that the functioning of working memory was impaired in multiple sclerosis in the executive functions of divided attention and updating when the group of persons living with MS and the control group were compared. In addition, the performance in the four executive functions analyzed did not show the same profile across the persons living with MS in the sample, as no deficit in attentional shifting or inhibition was observed. It can be concluded that the presence of deficits was observed only in the executive functions of divided attention and updating under the condition of greater cognitive demand. The clinical implications of these results are underlined due to their impact on daily life.
Changes in alpha band activity (8-12 Hz) indicate the inhibition of brain regions during cognitive tasks, reflecting real-time cognitive load. Despite this, its feasibility to be used in a more dynamic environment with ongoing motor corrections has not been studied. This research used electroencephalography (EEG) to explore how different brain regions are engaged during a simple grasp and lift task where unexpected changes to the object's weight or surface friction are introduced. The results suggest that alpha activity changes related to motor error correction occur only in motor-related areas (i.e. central areas), but not in error processing areas (ie. fronto-parietal network) during unexpected weight changes. This suggests that oscillations over motor areas reflect reduction of motor drive related to motor error correction, thus being a potential cortical electrophysiological biomarker for the process, and not solely as a proxy for cognitive demands. This observation is particularly relevant in scenarios where these signals are used to evaluate high cognitive demands co-occurring with high levels of motor errors and corrections, such as prosthesis use. The establishment of electrophysiological biomarkers of mental resource allocation during movement and cognition can help identify indicators of mental workload and motor drive, which may be useful for improving brain-machine interfaces.
The striatum is thought to play an essential role in the acquisition of a wide range of motor, perceptual, and cognitive skills, but neuroimaging has not yet demonstrated striatal activation during nonmotor skill learning. Functional magnetic resonance imaging was performed while participants learned probabilistic classification, a cognitive task known to rely on procedural memory early in learning and declarative memory later in learning. Multiple brain regions were active during probabilistic classification compared with a perceptual-motor control task, including bilateral frontal cortices, occipital cortex, and the right caudate nucleus in the striatum. The left hippocampus was less active bilaterally during probabilistic classification than during the control task, and the time course of this hippocampal deactivation paralleled the expected involvement of medial temporal structures based on behavioral studies of amnesic patients. Findings provide initial evidence for the role of frontostriatal systems in normal cognitive skill learning.
Purpose:
The purpose of this study was to investigate auditory verbal working memory in adults who do (AWS) and do not (AWNS) stutter using a highly demanding linguistic N-back task.
Methods:
Fifteen AWS and 15 AWNS matched in age, gender and educational level were asked to hear series of words and respond by pressing a "yes" button if the word they just heard was the same as the word one, two, or three trials back. Words were either phonologically similar (i.e., Phonological Linguistic Condition) or phonologically dissimilar (i.e., Neutral Linguistic Condition). Accuracy and false alarms rates as well as reaction time on correct target trials, missed target trials and false alarms were collected and analyzed.
Results:
Differences were not found between AWS and AWNS in accuracy. Both groups were more accurate and significantly faster in 1- followed by 2- followed by 3-back trials. However, AWS were significantly slower than AWNS in the 2-back level, regardless of linguistic condition. Furthermore, AWS demonstrated more false alarms compared to AWNS.
Conclusion:
Results revealed differences in auditory verbal working memory and interference control between AWS and AWNS when processing highly linguistically demanding stimuli.
Learning to control behavior when receiving feedback underlies social adaptation in childhood and adolescence, and is potentially strengthened by environmental support factors, such as parents. This study examined the neural development of responding to social feedback from childhood to adolescence, and effects of parental sensitivity on this development. We studied these questions in a 3-wave longitudinal fMRI sample (ages 7-13 years, n = 512). We measured responses to feedback using the fMRI Social Network Aggression Task through noise blasts following peer feedback and associated neural activity, and parental sensitivity using observations of parent-child interactions during Etch-a-Sketch. Results revealed largest reductions in noise blasts following positive feedback between middle and late childhood and following negative feedback between late childhood and early adolescence. Additionally, brain-behavior associations between dorsolateral prefrontal cortex activation and noise blast durations became more differentiated across development. Parental sensitivity was only associated with noise blast duration following positive feedback in childhood, but not in adolescence. There was no relation between parental sensitivity and neural activity. Our findings contribute to our understanding of neural development and individual differences in responding to social feedback, and the role of parenting in supporting children's adaption to social feedback.
Aim: Acute sleep deprivation has revealed altered executive cognitive functioning, including attention, working memory, and interference resolution. In the present study, we investigated brain hemodynamics and cognitive function measures using functional near-infrared spectroscopy (fNIRS).
Methods: fNIRS was used to record cortical brain activity in a resting state scan, flanker task, and n-Back tasks under well-rested (WR, >6.5 h sleep for ≥3 days) and sleep-deprived conditions (SD, 28 h awake) in a repeated-measures study in 20 participants (7 female, mean age 20.1 ± 0.413).
Results: Our results indicate decreased accuracy rates in the flanker task in the SD condition, suggesting reduced response inhibition capacity. In the flanker task, a significant increase of beta estimates was observed in the SD condition in the right dl-PFC, suggesting potential compensation (BH-FDR corrected p = 0.0418, t(19) = 3.51). There were no significant differences between WR and SD in n-back task accuracy rates or reaction times or in Flanker task reaction times. Otherwise, functional connectivity strengths were not significantly different between the WR and SD sessions on a group-level analysis for the resting state and all tasks (BH-FDR correction, p > 0.05).
Conclusion: Our results provide insight into how insufficient sleep patterns affect interference resolution, and that fNIRS can reveal functional connectivity differences inter- and intra-individually in SD conditions.
We report an experiment that assesses the effect of variations in memory load on brain activations that mediate verbal working memory. The paradigm that forms the basis of this experiment is the "n-back" task in which subjects must decide for each letter in a series whether it matches the one presented n items back in the series. This task is of interest because it recruits processes involved in both the storage and manipulation of information in working memory. Variations in task difficulty were accomplished by varying the value of n. As n increased, subjects showed poorer behavioral performance as well as monotonically increasing magnitudes of brain activation in a large number of sites that together have been identified with verbal working-memory processes. By contrast, there was no reliable increase in activation in sites that are unrelated to working memory. These results validate the use of parametric manipulation of task variables in neuroimaging research, and they converge with the subtraction paradigm used most often in neuroimaging. In addition, the data support a model of working memory that includes both storage and executive processes that recruit a network of brain areas, all of which are involved in task performance.
The past five years have seen an outpouring of neuroimaging studies of memory — using both positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). These studies have convincingly demonstrated that neuroimaging can be used to study the functional anatomy of normal human memory and that neuroimaging can precisely localize memory related brain activations within small areas of cortex. As one illustration of the application of neuroimaging in the study of memory, this review shows how several laboratories have produced data that converge on the notion that specific areas in the prefrontal cortex are active during long-term memory retrieval. Moreover, the data further suggest that distinct prefrontal brain areas might make differential contributions to different kinds of long-term memory retrieval.
Examines the possibility that the components of an information-processing system all operate continuously, passing information from one to the next as it becomes available. A model called the "cascade model" is presented and shown to be compatible with the general form of the relation between time and accuracy in speed–accuracy trade-off experiments. In the model, experimental manipulations may have either or both of 2 effects on a processing level: They may alter the rate of response or the asymptotic quality of the output. The effects of such manipulations on the output of a system of processes is described. The model is then used to reexamine the subtraction and additive factors methods for analyzing the composition of systems of processes. Results include the finding that factors that affect the rates of 2 different processes would be expected to have additive effects on reaction times under the cascade model, whereas 2 factors that both affect the rate of the same process would tend to interact, just as in the case in which the manipulations affect the durations of discrete stages. Factors that affect asymptotic output, however, tend to interact whether they affect the same or different processes. A new method is presented for analyzing processes in cascade, which extends the additive factors method to an analysis of the parameters of the function relating response time and accuracy. (70 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Monotonic hypotheses are predictions about the ordering of group population means. A journal survey revealed that the problem was very common and that there was little uniformity among researchers regarding the statistical test to use. Most of the approaches in the literature to detect both monotonic trend and nonmonotonicity were compared under varying population conditions in a Monte Carlo simulation. The results suggested that only rarely will sample means order the same as the corresponding population means, leaving the approaches most researchers used with far too little power. Trend tests had far greater power; the one recommended is the familiar linear trend test. However, used alone this test does not detect the presence of any instances of nonmonotonicity. Therefore, it should be used in combination with a technique that can detect such inversions, preferably the Sidák-corrected reversal test conducted with a very high α (.50). (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Reviews the relationship between neuropsychological approaches to human memory and the working memory theory introduced by A. D. Baddeley and G. J. Hitch (1974). It is argued that neuropsychological perspectives have made a number of different contributions to the development of the theory. On occasion, they have provided unique natural experiments that cannot be simulated in the laboratory and that represent a significant input to theoretical refinement. They also yield a rich source of information on a central tenet of working memory theory, which is that the components of working memory support everyday complex cognitive activities. Neuropsychological studies have played an important role in identifying the contributions of the phonological loop to the acquisition and processing of language and of the visuospatial sketchpad to learning to recognize new faces. More generally, neuropsychological investigations have substantially reinforced developments of theory based on work from the experimental laboratory, and they provide convincing evidence for the robustness and generality of the theory. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
PsyScope is an integrated environment for designing and running psychology experiments on Macintosh computers. The primary
goal of PsyScope is to give both psychology students and trained researchers a tool that allows them to design experiments
without the need for programming. PsyScope relies on the interactive graphic environment provided by Macintosh computers to
accomplish this goal. The standard components of a psychology experiment—groups, blocks, trials, and factors—are all represented
graphically, and experiments are constructed by working with these elements in interactive windows and dialogs. In this article,
we describe the overall organization of the program, provide an example of how a simple experiment can be constructed within
its graphic environment, and discuss some of its technical features (such as its underlying scripting language, timing characteristics,
etc.). PsyScope is available for noncommercial purposes free of charge and unsupported to the general research community.
Information about how to obtain the program and its documentation is provided.
When subjects judge whether a test symbol is contained in a short memorized sequence of symbols, their mean reaction-time
increases linearly with the length of the sequence. The linearity and slope of the function imply the existence of an internal
serial-comparison process whose average rate is between 25 and 30 symbols per second.
Neuronal activity causes local changes in cerebral blood flow, blood volume, and blood oxygenation. Magnetic resonance imaging (MRI) techniques sensitive to changes in cerebral blood flow and blood oxygenation were developed by high-speed echo planar imaging. These techniques were used to obtain completely noninvasive tomographic maps of human brain activity, by using visual and motor stimulus paradigms. Changes in blood oxygenation were detected by using a gradient echo (GE) imaging sequence sensitive to the paramagnetic state of deoxygenated hemoglobin. Blood flow changes were evaluated by a spin-echo inversion recovery (IR), tissue relaxation parameter T1-sensitive pulse sequence. A series of images were acquired continuously with the same imaging pulse sequence (either GE or IR) during task activation. Cine display of subtraction images (activated minus baseline) directly demonstrates activity-induced changes in brain MR signal observed at a temporal resolution of seconds. During 8-Hz patterned-flash photic stimulation, a significant increase in signal intensity (paired t test; P less than 0.001) of 1.8% +/- 0.8% (GE) and 1.8% +/- 0.9% (IR) was observed in the primary visual cortex (V1) of seven normal volunteers. The mean rise-time constant of the signal change was 4.4 +/- 2.2 s for the GE images and 8.9 +/- 2.8 s for the IR images. The stimulation frequency dependence of visual activation agrees with previous positron emission tomography observations, with the largest MR signal response occurring at 8 Hz. Similar signal changes were observed within the human primary motor cortex (M1) during a hand squeezing task and in animal models of increased blood flow by hypercapnia. By using intrinsic blood-tissue contrast, functional MRI opens a spatial-temporal window onto individual brain physiology.
The human brain localizes mental operations of the kind posited by cognitive theories. These local computations are integrated
in the performance of cognitive tasks such as reading. To support this general hypothesis, new data from neural imaging studies
of word reading are related to results of studies on normal subjects and patients with lesions. Further support comes from
studies in mental imagery, timing, and memory.
Previous studies of remote memory function have indicated a dissociability between memory for the content and date of past events and suggested selective deficits of dating capacity in Parkinson's disease (PD). The present study examined the hypothesis that poor dating in PD is linked to a specific deficit in temporal contextual memory which also affects new learning. Patients with PD and patients with Alzheimer's disease (AD) were compared in their ability to perform tasks of content recognition and recency discrimination of words presented sequentially. Compared with AD patients, PD patients were disproportionately impaired in recency discrimination relative to content recognition. When performance was analysed as a function of retention interval, AD patients showed impairment in both tasks at all intervals. PD patients, by contrast, showed deficits in content recognition at the short stimulus-test intervals only, possibly reflecting the clinical phenomenon of bradyphrenia. These results suggest that recency discrimination deficits and impaired short-term memory processing are specific cognitive deficits in PD that may be linked to subcortical deafferentation of the frontal lobes.
Unit recording studies in the lateral bank of the intraparietal cortex (area LIP) have demonstrated a response property not previously reported in posterior cortex. Studies were performed in the Rhesus monkey during tasks which required saccadic eye movements to remembered target locations in the dark. Neurons were found which remained active during the time period for which the monkey had to withhold eye movements while remembering desired target locations. The activity of the cells was tuned for eye movements of specific direction and amplitude, and it was not necessary for a visual stimulus to fall within the response field. The responses appeared to represent a memory-related motor-planning signal encoding motor error. The relation of the activity to the behavior of the animal suggests that the response represents the intent to make eye movements of specific direction and amplitude.
The relationship of single unit activity to limb movements guided by visuospatial cues supports the view that the premotor cortex is a distinct cortical field within the somatic sensorimotor cortex. The premotor cortex is similar to the precentral motor cortex (MI) in that most of its units are clearly related to voluntary movements but differs from MI by its higher threshold for microstimulation-evoked movements, its cytoarchitecture, and the presence of a larger population of neurons with activity related to the occurrence of visuospatial signals rather than, or in addition to, the movement cued by those signals.
Single-cell activity was recorded in the inferotemporal cortex of monkeys performing a task that requires perception and temporary
retention of colored stimuli. Many cells reacted differentially to the stimuli. By changing the relevance of certain features
of compound stimuli, it was found that the reactions of some cells to color depend critically on whether or not the task demands
that the animal pay attention to color. A substantial number of cells showed color-dependent differences in frequency of discharge
during the retention periods of the task. The temporal characteristics of differential discharge and its dissolution when
memory is no longer required indicate that the cells that display it are involved in retaining visual information.
A delayed match-to-sample (DMS) task of abstract, visual memory was performed during the uptake period of 18F-fluorodeoxyglucose. The increase in glucose uptake of cortical and subcortical regions ("activation") during the DMS task was compared with that during a control, immediate match-to-sample task using positron emission tomography. Both discriminant analysis and paired t tests supported the observation that the dorsolateral prefrontal area underwent the greatest activation, while a factor analysis revealed the functional correlation matrices of the tasks. Activations in the ventral premotor cortex and supramarginal and angular gyri were highly correlated with the change in the dorsolateral prefrontal cortex. The basal forebrain/ventral pole region showed a smaller but independently significant change. The findings support the role of the dorsal prefrontal region in the nonspatial working memory of humans.
Using noninvasive functional magnetic resonance imaging (fMRI) technique, we analyzed the responses in human area MT with regard to visual motion, color, and luminance contrast sensitivity, and retinotopy. As in previous PET studies, we found that area MT responded selectively to moving (compared to stationary) stimuli. The location of human MT in the present fMRI results is consistent with that of MT in earlier PET and anatomical studies. In addition we found that area MT has a much higher contrast sensitivity than that in several other areas, including primary visual cortex (V1). Functional MRI half-amplitudes in V1 and MT occurred at approximately 15% and 1% luminance contrast, respectively. High sensitivity to contrast and motion in MT have been closely associated with magnocellular stream specialization in nonhuman primates. Human psychophysics indicates that visual motion appears to diminish when moving color-varying stimuli are equated in luminance. Electrophysiological results from macaque MT suggest that the human percept could be due to decreases in firing of area MT cells at equiluminance. We show here that fMRI activity in human MT does in fact decrease at and near individually measured equiluminance. Tests with visuotopically restricted stimuli in each hemifield produced spatial variations in fMRI activity consistent with retinotopy in human homologs of macaque areas V1, V2, V3, and VP. Such activity in area MT appeared much less retinotopic, as in macaque. However, it was possible to measure the interhemispheric spread of fMRI activity in human MT (half amplitude activation across the vertical meridian = approximately 15 degrees).
High-speed magnetic resonance (MR) imaging was used to detect activation in the human prefrontal cortex induced by a spatial working memory task modeled on those used to elucidate neuronal circuits in nonhuman primates. Subjects were required to judge whether the location occupied by the current stimulus had been occupied previously over a sequence of 14 or 15 stimuli presented in various locations. Control tasks were similar in all essential respects, except that the subject's task was to detect when one of the stimuli presented was colored red (color detection) or when a dot briefly appeared within the stimulus (dot detection). In all tasks, two to three target events occurred randomly. The MR signal increased in an area of the middle frontal gyrus corresponding to Brodmann's area 46 in all eight subjects performing the spatial working memory task. Right hemisphere activation was greater and more consistent than left. The MR signal change occurred within 6-9 sec of task onset and declined within a similar period after task completion. An increase in MR signal was also noted in the control tasks, but the magnitude of change was less than that recorded in the working memory task. These differences were replicated when testing was repeated in five of the original subjects. The localization of spatial working memory function in humans to a circumscribed area of the middle frontal gyrus supports the compartmentalization of working memory functions in the human prefrontal cortex and the localization of spatial memory processes to comparable areas in humans and nonhuman primates.
Monkeys were trained to perform a delayed response (DR) task. A visual cue—placement of food under one of two test objects—was succeded by a delay of 18 sec, during which the test objects were concealed and out of reach. At the end of the delay, the objects were made accessible for choice and, if the choice was correct, for reward.Single unit activity was recorded from thalamic nuclei during DR performance. The parvo- and magnocelularis portions of the nucleus medialis dorsalis (MD) were principally explored. Units spontaneously exhibiting rhytmic firing were commonly observed, particularly in MD pars magnocellularis. According to temporal patterns of firing frequency changes during DR trials, 6 different types of units were distinguished. Approximately one-half of all the units sampled in MD, pars parvocellularis, showed sustained elevations of discharge during the delay. These findings are comparable to those made in a separate study of the prefrontal cortical area to which MD, pars parvocellularis, is connected.The firing changes correlated with the behavioral task are interpreted as manifestations of a functional involvement of MD, together with the prefrontal cortex, in DR performance. The possible nature of this involvement is discussed in relation to the available evidence from anatomical, electrophysiological and behavioral research.
Current cognitive models of verbal working memory include two components a phonological store and a rehearsal mechanism that refreshes the contents of this store We present research using positron emission tomography (PET) to provide further evidence for this functional division In Experiment 1, subjects performed a variant of Sternberg's (1966) item recognition task Experiment 2 used a continuous memory task with control conditions designed to separate the brain regions underlying storage and rehearsal The results show that independent brain regions mediate storage and rehearsal In Experiment 3, a dual-task procedure supported the assumption that these memory tasks elicited a rehearsal strategy
Humans can monitor actions and compensate for errors. Analysis of the human event-related brain potentials (ERPs) accompanying errors provides evidence for a neural process whose activity is specifically associated with monitoring and compensating for erroneous behavior. This error-related activity is enhanced when subjects strive for accurate performance but is diminished when response speed is emphasized at the expense of accuracy. The activity is also related to attempts to compensate for the erroneous behavior.
Neuropsychological results are increasingly cited in cognitive theories although their methodology has been severely criticised. The book argues for an eclectic approach but particularly stresses the use of single-case studies. A range of potential artifacts exists when inferences are made from such studies to the organisation of normal function – for example, resource differences among tasks, premorbid individual differences, and reorganisation of function. The use of “strong” and “classical” dissociations minimises potential artifacts. The theoretical convergence between findings from fields where cognitive neuropsychology is well developed and those from the normal literature strongly suggests that the potential artifacts are not critical. The fields examined in detail in this respect are short-term memory, reading, writing, the organisation of input and output speech systems, and visual perception. Functional dissociation data suggest that not only are input systems organised modularly, but so are central systems. This conclusion is supported by findings on impairment of knowledge, visual attention, supervisory functions, memory, and consciousness.
Functional magnetic resonance imaging (fMRI) was used to record cortical activation across multiple stages in the visual system during single character visual search and reversing checkerboard stimulation. Scanning used T2-weighted, gradient echo sequences with late echo times (TE = 36 ms) with a voxel size of 0.94 * 1.88 mm in-plane resolution, 4–5 mm deep, on a conventional scanner. A scout experiment recorded six slices to identify major regions of activation. Two slices were selected for extensive assessment. Character stimuli activated small (average 16 mm2), reliable, statistically defined regions of activation in the calcarine fissure, superior occipital cortex, and fusiform-lingual gyrus. The results include: (1) for character search, the MRI signal change increased linearly from 2.1 to 3.1% for stimulation from 1 to 8 Hz; (2) the character rate effect was equivalent across three levels of the visual system; (3) the checkerboard stimuli showed broader, more intense primary visual activation and less intense secondary visual activation than did character search. Issues relating to fMRI signal variability across the imagining plane, statistical data analysis, signal sensitivity, statistical power, fMRI experimental protocols, and comparisons with positron emission tomography (PET) data are discussed. © 1994 Wiley-Liss, Inc.
The sections in this article are:
The typical functional magnetic resonance (fMRI) study presents a formidable problem of multiple statistical comparisons (i.e, > 10,000 in a 128 x 128 image). To protect against false positives, investigators have typically relied on decreasing the per pixel false positive probability. This approach incurs an inevitable loss of power to detect statistically significant activity. An alternative approach, which relies on the assumption that areas of true neural activity will tend to stimulate signal changes over contiguous pixels, is presented. If one knows the probability distribution of such cluster sizes as a function of per pixel false positive probability, one can use cluster-size thresholds independently to reject false positives. Both Monte Carlo simulations and fMRI studies of human subjects have been used to verify that this approach can improve statistical power by as much as fivefold over techniques that rely solely on adjusting per pixel false positive probabilities.
Functional magnetic resonance imaging (fMRI) was used to examine the pattern of activity of the prefrontal cortex during performance of subjects in a nonspatial working memory task. Subjects observed sequences of letters and responded whenever a letter repeated with exactly one nonidentical letter intervening. In a comparison task, subjects monitored similar sequences of letters for any occurrence of a single, prespecified target letter. Functional scanning was performed using a newly developed spiral scan image acquisition technique that provides high-resolution, multislice scanning at approximately five times the rate usually possible on conventional equipment (an average of one image per second). Using these methods, activation of the middle and inferior frontal gyri was reliably observed within individual subjects during performance of the working memory task relative to the comparison task. Effect sizes (2–4%) closely approximated those that have been observed within primary sensory and motor cortices using similar fMRI techniques. Furthermore, activation increased and decreased with a time course that was highly consistent with the task manipulations. These findings corroborate the results of positron emission tomography studies, which suggest that the prefrontal cortex is engaged by tasks that rely on working memory. Furthermore, they demonstrate the applicability of newly developed fMRI techniques using conventional scanners to study the associative cortex in individual subjects. © 1994 Wiley-Liss, Inc.
A theory of the way working memory capacity constrains comprehension is proposed. The theory proposes that both processing and storage are mediated by activation and that the total amount of activation available in working memory varies among individuals. Individual differences in working memory capacity for language can account for qualitative and quantitative differences among college-age adults in several aspects of language comprehension. One aspect is syntactic modularity: The larger capacity of some individuals permits interaction among syntactic and pragmatic information, so that their syntactic processes are not informationally encapsulated. Another aspect is syntactic ambiguity: The larger capacity of some individuals permits them to maintain multiple interpretations. The theory is instantiated as a production system model in which the amount of activation available to the model affects how it adapts to the transient computational and storage demands that occur in comprehension.
A computer algorithm for the three-dimensional (3D) alignment of PET images is described. To align two images, the algorithm calculates the ratio of one image to the other on a voxel-by-voxel basis and then iteratively moves the images relative to one another to minimize the variance of this ratio across voxels. Since the method relies on anatomic information in the images rather than on external fiducial markers, it can be applied retrospectively. Validation studies using a 3D brain phantom show that the algorithm aligns images acquired at a wide variety of positions with maximum positional errors that are usually less than the width of a voxel (1.745 mm). Simulated cortical activation sites do not interfere with alignment. Global errors in quantitation from realignment are less than 2%. Regional errors due to partial volume effects are largest when the gantry is rotated by large angles or when the bed is translated axially by one-half the interplane distance. To minimize such partial volume effects, the algorithm can be used prospectively, during acquisition, to reposition the scanner gantry and bed to match an earlier study. Computation requires 3-6 min on a Sun SPARCstation 2.
Information about the basal ganglia has accumulated at a prodigious pace over the past decade, necessitating major revisions in the authors' concepts of the structural and functional organization of these nuclei. Recent anatomical and physiological findings have further substantiated the concept of segregated basal ganglia-thalamocortical pathways, and reinforced the general principle that basal ganglia influences are transmitted only to restricted portions of the frontal lobe (even though the striatum receives projections from nearly the entire neocortex). Using the 'motor' circuit as a model, the authors have reexamined the available data on other portions of the basal ganglia-thalamocortical pathways and found that the evidence strongly suggests the existence of at least four additional circuits organized in parallel with the 'motor' circuit. In the discussion that follows, they review some of the anatomic and physiologic features of the 'motor circuit,' as well as the data that support the existence of the other proposed parallel circuits, which they have designated the 'oculomotor,' the 'dorsolateral prefrontal,' the 'lateral orbitofrontal,' and the 'anterior cingulate,' respectively. Each of these five basal ganglia-thalamocortical circuits appears to be centered upon a separate part of the frontal lobe. This list of basal ganglia-thalamocortical circuits is not intended to be exhaustive. In fact, if the conclusions suggested in this review are valid, future investigations might be expected to disclose not only further details (or the need for revisions) of these five circuits, but perhaps also the existence of additional parallel circuits whose identification is currently precluded by a paucity of data.
The sources of afferent input to the striatum (caudate nucleus and putamen) suggest that this structure may be engaged in neuronal processes related to the initiation of movement. We found that 26% of 508 neurons in both parts of the striatum were activated during the presentation of visual signals which prepared the animals for the execution or withholding of individual arm reaching movements. In a second task, 20% of 382 striatal neurons were activated up to 3 s before self-initiated, non automatic and purposive arm movements which were performed in the complete absence of phasic external stimuli. The data demonstrate an involvement of the striatum in externally and internally generated processes which are related to presetting mechanisms during the initiation of behavioral acts.
The time required to recognize that two perspective drawings portray objects of the same three-dimensional shape is found
to be (i) a linearly increasing function of the angular difference in the portrayed orientations of the two objects and (ii)
no shorter for differences corresponding simply to a rigid rotation of one of the two-dimensional drawings in its own picture
plane than for differences corresponding to a rotation of the three-dimensional object in depth.
The typical functional magnetic resonance (fMRI) study presents a formidable problem of multiple statistical comparisons (i.e., > 10,000 in a 128 x 128 image). To protect against false positives, investigators have typically relied on decreasing the per pixel false positive probability. This approach incurs an inevitable loss of power to detect statistically significant activity. An alternative approach, which relies on the assumption that areas of true neural activity will tend to stimulate signal changes over contiguous pixels, is presented. If one knows the probability distribution of such cluster sizes as a function of per pixel false positive probability, one can use cluster-size thresholds independently to reject false positives. Both Monte Carlo simulations and fMRI studies of human subjects have been used to verify that this approach can improve statistical power by as much as fivefold over techniques that rely solely on adjusting per pixel false positive probabilities.
Working memory (WM), the ability to momentarily maintain information in an active state, is central to higher cognitive functions. The processes involved in WM operate on a sub-second timescale, and thus evoked potential measures have an appropriate temporal resolution for studying them. In the experiment reported here, evoked potential covariances (EPC) between scalp recording sites were computed for a task requiring maintenance of numeric information in WM; these EPCs were compared to those observed in a control task which had the same stimuli and responses but less of a WM requirement. EPC patterns differed between conditions prior to the stimulus, and in an interval spanning the P300 peak in the match detection trials which required response inhibition. The pattern of prestimulus EPCs was more complex and left-sided in the WM task, when memory codes were being maintained and responses contingent on those codes were being prepared. P300 peak latency was 140 msec shorter in the WM task, and the P300 EPC pattern was more anterior and left-sided. In contrast, EPC patterns did not differ during early stages of stimulus processing or during response execution. These results suggest that distinct EPC patterns associated with WM only occur during intervals in which the information in an active state is being utilized for task performance.
Brain function can be mapped with magnetic resonance (MR) imaging sensitized to regional changes in blood oxygenation due to cortical activation. Several MR imaging methods, including conventional imaging and echo-planar imaging, have been successfully used for this purpose. The authors investigated spiral k-space MR imaging, implemented with an unmodified 1.5-T clinical imager, for imaging of cortical activation. A gradient-echo, spiral k-space imaging method was used to measure activation in the primary visual cortex (number sequence task), primary motor cortex (fist-clenching task), and prefrontal cortex (verbal fluency task). Comparison of conventional and spiral k-space imaging in the visual and motor cortex, in which signal-to-noise ratio, voxel size, and imaging time were matched, showed that artifacts were reduced with the spiral k-space method, while the area and degree of activation were similar. The number of sections that could be imaged in a fixed time interval was increased by a factor of four with this implementation of spiral k-space imaging compared with conventional imaging.
Positron emission tomography measurements of regional cerebral blood flow (rCBF) were performed in normal volunteers during a graded auditory-verbal memory task. Subjects were required to remember and then immediately, and freely, recall a series of auditorily presented word lists varying from two to 13 words in length. Significant regional correlations between rCBF and memory load (word list length) were identified using statistical parametric mapping. Increasing memory load correlated with increasing rCBF in the cerebellar vermis and hemispheres, thalamus bilaterally, the superior and middle frontal gyri bilaterally, anterior insular regions bilaterally, anterior cingulate, precuneus and left and right lateral premotor areas. Increasing memory load also correlated with decreasing rCBF in the left and right superior temporal/insular regions, medial frontal gyrus, Brodmann's area 37 bilaterally, cuneus, inferior parietal lobule bilaterally and the mid-portion of the cingulate cortex. The pattern of rCBF change closely resembled that identified in a previously reported study using a cognitive subtraction paradigm and provides further evidence for a widespread neural system subserving auditory-verbal memory. The patterns of rCBF response suggest that the areas identified are associated with limited capacity processes for encoding and retrieval.
