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Lateral Interactions in Primary Visual Cortex: A Model Bridging Physiology and Psychophysics
Abstract
Recent physiological studies show that the spatial context of visual stimuli enhances the response of cells in primary visual cortex to weak stimuli and suppresses the response to strong stimuli. A model of orientation-tuned neurons was constructed to explore the role of lateral cortical connections in this dual effect. The differential effect of excitatory and inhibitory current and noise conveyed by the lateral connections explains the physiological results as well as the psychophysics of pop-out and contour completion. Exploiting the model's property of stochastic resonance, the visual context changes the model's intrinsic input variability to enhance the detection of weak signals.
... Furthermore, the activation pattern observed in CNN is also consistent with the principle of lateral interaction in the visual cortex [41], which includes intermediate excitation and lateral inhibition. ...
... The proposed mode-locked pattern aligns with the principle of lateral interaction in the visual cortex [41], which involves intermediate excitation and lateral inhibition. The lateral inhibition enhances object separation from their visual backgrounds, especially for object boundaries and outlines, improving visual sensitivity and contrast differences. ...
... The resulting activation pattern aligns with the mode-locking pattern and lateral interactions in the visual cortex. (e) Long-range lateral interaction map obtained by optical imaging in a macaque monkey[41]. Each pixel's color corresponds to the preferred orientation of the respective cell (yellow, horizontal; green, 45 • ; red, 90 • ; and blue, 135 • ). ...
Visual long-range interaction refers to modeling dependencies between distant feature points or blocks within an image, which can significantly enhance the model's robustness. Both CNN and Transformer can establish long-range interactions through layering and patch calculations. However, the underlying mechanism of long-range interaction in visual space remains unclear. We propose the mode-locking theory as the underlying mechanism, which constrains the phase and wavelength relationship between waves to achieve mode-locked interference waveform. We verify this theory through simulation experiments and demonstrate the mode-locking pattern in real-world scene models. Our proposed theory of long-range interaction provides a comprehensive understanding of the mechanism behind this phenomenon in artificial neural networks. This theory can inspire the integration of the mode-locking pattern into models to enhance their robustness.
... É importante salientar que o processamento de feedback após a execução de ações faz parte do funcionamento de cada controlador neural. Como explicado na seção inicial desse artigo, estudos neuroanatômicos também apontam a existência de conexões laterais ligando circuitos neurais paralelos (BARBAS, 2015;BASTOS et al., 2012;HABER, 2003;WISE, 2012;PETRIDES;PANDYA, 1999;STEMMLER;USHER;NIEBUR, 1995;ZEKI;SHIPP, 1988 (BARDELLA et al., 2016;BASTOS et al., 2012;FRISTON, 2008;KIEBEL, 2009;HUANG;RAO, 2011;BALLARD, 1999). De acordo com esse modelo, as regiões cerebrais de maior hierarquia enviam sinais de previsão/antecipatórios, por meio de conexões antecipatórias, indicando o que espera da regiões de menor hierarquia. ...
... É importante salientar que o processamento de feedback após a execução de ações faz parte do funcionamento de cada controlador neural. Como explicado na seção inicial desse artigo, estudos neuroanatômicos também apontam a existência de conexões laterais ligando circuitos neurais paralelos (BARBAS, 2015;BASTOS et al., 2012;HABER, 2003;WISE, 2012;PETRIDES;PANDYA, 1999;STEMMLER;USHER;NIEBUR, 1995;ZEKI;SHIPP, 1988 (BARDELLA et al., 2016;BASTOS et al., 2012;FRISTON, 2008;KIEBEL, 2009;HUANG;RAO, 2011;BALLARD, 1999). De acordo com esse modelo, as regiões cerebrais de maior hierarquia enviam sinais de previsão/antecipatórios, por meio de conexões antecipatórias, indicando o que espera da regiões de menor hierarquia. ...
... É importante salientar que o processamento de feedback após a execução de ações faz parte do funcionamento de cada controlador neural. Como explicado na seção inicial desse artigo, estudos neuroanatômicos também apontam a existência de conexões laterais ligando circuitos neurais paralelos (BARBAS, 2015;BASTOS et al., 2012;HABER, 2003;WISE, 2012;PETRIDES;PANDYA, 1999;STEMMLER;USHER;NIEBUR, 1995;ZEKI;SHIPP, 1988 (BARDELLA et al., 2016;BASTOS et al., 2012;FRISTON, 2008;KIEBEL, 2009;HUANG;RAO, 2011;BALLARD, 1999). De acordo com esse modelo, as regiões cerebrais de maior hierarquia enviam sinais de previsão/antecipatórios, por meio de conexões antecipatórias, indicando o que espera da regiões de menor hierarquia. ...
Human survival and social interactions are highly dependent on the selection of sequential actions. Despite recent technological advances to record neural activity and recent findings demonstrating how the brain controls and organizes sequential actions, a broader theoretical approach is needed to integrate the theoretical advances and the experimental evidence that best explains the neural control of human sequential behavior. This opinion piece will discuss the recent neuroscientific findings that revealed the existence of parallel neural circuits implicated in the control of sequential actions. It will be argued that these parallel neural circuits are, in fact, neural controllers specialized at implementing action selection strategies and that such strategies assume behavior control in a context-dependent manner according to an individual’s experience. This opinion will also present behavioral evidence supporting the existence of three action selection strategies (exploratory, model-based, habit-based) and functional neuroimaging evidence demonstrating how these strategies are realized by distinct neural controllers linking the prefrontal cortex, the basal ganglia and the cerebellum. Finally, the parallel model of neural control of action selection will be extended into a hierarchical model where different controllers, represented by parallel neural circuits, work independently and also share information that supports controller arbitration.
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... Indeed, previous studies suggest that training the contrastdetection task of a Gabor patch performed in a lateral masking regimen produces training-induced cortical plasticity (Maniglia, Soler, Cottereau, & Trotter, 2018), outside the critical period (Sagi, 2011), at the level of the early visual cortices (Gilbert & Wiesel, 1985;Grinvald, Lieke, Frostig, & Hildesheim, 1994;Ts'o, Gilbert, & Wiesel, 1986). This task is mediated by the activation of excitatory (E) and inhibitory (I) subpopulations of neurons in a cortical column of the primary visual cortex, with the ratio between E and I activation increasing as a consequence of two inputs: target contrast (thalamic input) and the input from lateral cortical connections biased versus excitation (Adini, Sagi, & Tsodyks, 1997;Battaglini et al., 2019;Chen, Kasamatsu, Polat, & Norcia, 2001;Polat, 1999;Polat, Mizobe, Pettet, Kasamatsu, & Norcia, 1998;Seriès, Lorenceau, & Frégnac, 2003;Stemmler, Usher, & Niebur, 1995). In particular, this last input can be modulated by lateral masking producing threshold elevation (E/I < 1) when flankers are presented close to the foveal target (< 2λ) and threshold reduction (E/I > 1) when they are presented at a distance between 3-6λ, with λ indicating the wavelength. ...
... If perceptual learning occurs, then two scenarios (not mutually exclusive) will be possible. PL will result either in a reduction of neural noise with a consequent increase in contrast gain for the target, or it will also produce an effect consisting of the modulation of collinear lateral interactions (excitation and/or inhibition exerted by the flankers), at the early cortical level, (Adini, Sagi, & Tsodyks, 2002;Battaglini et al., 2019;Lev & Polat, 2015;Seriès et al., 2003;Stemmler et al., 1995). ...
... On the other hand, for target contrast lower than that of the flankers, lateral input depends on target flanker separation and target contrast. It would be biased towards excitation when target and flankers separation ranges between 3 and 4λ and contrast is relatively low, whereas inhibition would prevail if target flanker separation is 2λ or smaller and the target contrast is relatively high (Adini et al., 2002;Battaglini et al., 2019;Chen et al., 2001;Seriès et al., 2003;Stemmler et al., 1995). The hypothesis that this mechanism may be modulated by PL both in organic and functional amblyopia implies that lateral input at early cortical level plays a role in both types of amblyopia. ...
Background:
Several visual functions are impaired in patients with oculocutaneous albinism (OCA) associated to albinistic bilateral amblyopia (ABA).
Objective:
In this study, we aimed at exploring whether perceptual learning (PL) can improve visual functions in albinism.
Method:
Six patients and six normal sighted controls, were trained in a contrast detection task with lateral masking. Participants were asked to choose which of the two intervals contained a foveally presented low-contrast Gabor patch. Targets were presented between higher contrast collinear flankers with equal spatial frequency. When increasing target-to-flanker distance, lateral interactions effect normally switches from inhibition to facilitation, up to no effect.
Results:
Our findings showed that before PL, only controls showed facilitation. After PL, results suggest that facilitatory lateral interactions are found both in controls as well as in albino patients. These results suggest that PL could induce higher processing efficiency at early cortical level. Moreover, PL positive effect seems to transfer to higher-level visual functions, but results were not very consistent among tasks (visual acuity, contrast sensitivity function, hyperacuity and foveal crowding).
Conclusions:
Although a small sample size was tested, our findings suggest a rehabilitative potential of PL in improving visual functions in albinism.
... The phenomenon of weak information being detected by noise is called stochastic resonance, and it can be found in various physical systems. Stemmler et al. [12] noted that in the mathematical model of the cerebral cortex, lateral input from the peripheral circuits can be a source of noise for stochastic resonance. Mao et al. [13] and Cossart et al. [14] found synchronization for noise that was conventionally thought to be random. ...
Binary decision models have been the subject of renewed research in recent years. In these models, agents follow a stochastic evolution where they must choose between two possible choices by taking into account the choices of their peers. Kirman explained the process of ant social herding using a simple model, and he conducted an interesting simulation. The fat-tail distribution in the security market is well known, but its causes have not been sufficiently clarified. The aim of this article is to clarify them by a very simple model. In this article, by establishing a simple security market model and by applying the model of Kirman, the fat tail observed for price fluctuations is reproduced. Recent research in neuroscience has shown that noise plays a positive roll and enables us to have a deeper understanding of a natural commonality between ants and traders. The beauty competition of Keynes is kept in mind, and it is shown that a cause of the fat tail is the balance between independence and interdependence of the economic agents. Using a natural computing algorithm called Kirman’s ant model, I conducted a time series analysis of finance that appears when simplifying the human “behavior of imitating others”. The results show that natural fat tails appear.
... Connections within a visual area-known as horizontal or lateral connections-are associated with more low level functions such as spatial sharpening, cross-feature competition and normalization, and small scale visual grouping (Jones, Grieve, Wang, & Sillito, 2001;Kim et al., 2019;Stemmler, Usher, & Niebur, 1995;Stettler, Das, Bennett, & Gilbert, 2002). ...
Behavioral studies suggest that recurrence in the visual system is important for processing degraded stimuli. There are two broad anatomical forms this recurrence can take, lateral or feedback, each with different assumed functions. Here we add four different kinds of recurrence — two of each anatomical form — to a feedforward convolutional neural network and find all forms capable of increasing the ability of the network to classify noisy digit images. Specifically, we take inspiration from findings in biology by adding predictive feedback and lateral surround suppression. To compare these forms of recurrence to anatomically-matched counterparts we also train feedback and lateral connections directly to classify degraded images. Counter-intuitively, we find that the anatomy of the recurrence is not related to its function: both forms of task-trained recurrence change neural activity and behavior similarly to each other and differently from their bio-inspired anatomical counterparts. By using several analysis tools frequently applied to neural data, we identified the distinct strategies used by the predictive versus task-trained networks. Specifically, predictive feedback de-noises the representation of noisy images at the first layer of the network and decreases its dimensionality, leading to an expected increase in classification performance. Surprisingly, in the task-trained networks, representations are not de-noised over time at the first layer (in fact, they become `noiser' and dimensionality increases) yet these dynamics do lead to de-noising at later layers. The analyses used here can be applied to real neural recordings to identify the strategies at play in the brain. Our analysis of an fMRI dataset weakly supports the predictive feedback model but points to a need for higher-resolution cross-regional data to understand recurrent visual processing.
... In this review, we define membrane potential dynamics as the stochastically/deterministically shaped temporal structure of membrane potential (34,35) (Figure 1). The significance of membrane potential dynamics can be shaped by changes in hierarchical biophysical interactions (33), from microscopic [e.g., thermal noise (36), single-channel dwell time variability (37)(38)(39)] to mesoscopic [e.g., synaptic conductance variability (40)(41)(42)(43)(44)(45)] to macroscopic [e.g., the hierarchical interplay of multiple neurons (46)(47)(48)(49)] changes. ...
The circadian rhythm is a fundamental process that regulates the sleep–wake cycle. This rhythm is regulated by core clock genes that oscillate to create a physiological rhythm of circadian neuronal activity. However, we do not know much about the mechanism by which circadian inputs influence neurons involved in sleep–wake architecture. One possible mechanism involves the photoreceptor cryptochrome (CRY). In Drosophila, CRY is receptive to blue light and resets the circadian rhythm. CRY also influences membrane potential dynamics that regulate neural activity of circadian clock neurons in Drosophila, including the temporal structure in sequences of spikes, by interacting with subunits of the voltage-dependent potassium channel. Moreover, several core clock molecules interact with voltage-dependent/independent channels, channel-binding protein, and subunits of the electrogenic ion pump. These components cooperatively regulate mechanisms that translate circadian photoreception and the timing of clock genes into changes in membrane excitability, such as neural firing activity and polarization sensitivity. In clock neurons expressing CRY, these mechanisms also influence synaptic plasticity. In this review, we propose that membrane potential dynamics created by circadian photoreception and core clock molecules are critical for generating the set point of synaptic plasticity that depend on neural coding. In this way, membrane potential dynamics drive formation of baseline sleep architecture, light-driven arousal, and memory processing. We also discuss the machinery that coordinates membrane excitability in circadian networks found in Drosophila, and we compare this machinery to that found in mammalian systems. Based on this body of work, we propose future studies that can better delineate how neural codes impact molecular/cellular signaling and contribute to sleep, memory processing, and neurological disorders.
... The block-shaped condition can directly obtain a good performance by increasing the superimposed size (Fernandez-Rodriguez et al. 2019). Relevant physiological studies showed that a large visual stimuli can activate relatively large regions of the human visual field to engage the response of the neuronal cells (Schwartz 1977;Stemmler et al. 1995). In the present study, a red face combined with a colored rectangle as background constituted the new stimulus patterns, which took advantage of face and block-shape to improve the performance of visual-BCI systems. ...
Objective The stimulus color of P300-BCI systems has been successfully modified. However, the effects of different color combinations have not been widely investigated. In this study, we designed new stimulus patterns to evaluate the influence of color modulation on the BCI performance and waveforms of the evoked related potential (ERP).Methods Comparison was performed for three new stimulus patterns consisting of red face and colored block-shape, namely, red face with a white rectangle (RFW), red face with a blue rectangle (RFB), and red face with a red rectangle (RFR). Bayesian linear discriminant analysis (BLDA) was used to construct the individual classifier model. Repeated-measures ANOVA and Bonferroni correction were applied for statistical analysis. Results The RFW pattern obtained the highest average online accuracy with 96.94%, and those of RFR and RFB patterns were 93.61% and of 92.22% respectively. Significant differences in online accuracy and information transfer rate (ITR) were found between RFW and RFR patterns (p < 0.05). Conclusion Compared with RFR and RFB patterns, RFW yielded the best performance in P300-BCI. These new stimulus patterns with different color combinations have considerable importance to BCI applications and user-friendliness.
... According to it, contrast detection tasks are mediated by the activation of E, and I subpopulations of neurons in a cortical column, with the ratio between E and I activation increasing as a consequence of two inputs: stimulus contrast (thalamic input) and the lateral input biased versus excitation (Y. Adini et al., 1997;Chien Chung Chen, Kasamatsu, Polat, & Norcia, 2001;Chien Chung Chen & Tyler, 2002;Uri Polat, 1999;Seriès, Lorenceau, & Frégnac, 2003;Stemmler, Usher, & Niebur, 1995). ...
Macular degeneration (MD) is a common visual disorder in the aging population characterized by a loss of central vision, reduced visual acuity contrast sensitivity, and increased crowding. This impairment strongly affects the quality of life and personal autonomy. There is currently no cure for AMD, available treatment options are only able to slow down the disease, and even palliative treatments are rare. After the emergence of the central scotoma, patients with MD develop one or more eccentric fixation areas - preferred retinal loci (PRLs) - that are used for fixation, reading, tracking, and other visual tasks that require finer ocular abilities. The final goal of the project was to investigate and to improve the residual visual abilities in the PRL. Four studies were conducted in total. Study 1 was conducted in MD patients to investigate whether after the emergence of the scotoma, the PRL acquire enhanced abilities in the processing of the visual information through spontaneous or use-dependent adaptive plasticity. Study 2 aimed to assess the effects of a single administration of transcranial random noise electrical stimulation (tRNS), a subtype of non-invasive transcranial electrical stimulation, on the spatial integration in the healthy visual cortex. Study 3 aimed to assess the between session effect of daily repeated tRNS coupled with perceptual training. The objective of study 4 was to translate the previous findings into a clinically applicable treatment approach by combining tRNS and perceptual training in adult patients with MD. Contrary to previous results, we found neither a phenomenon of spontaneous nor use-dependent cortical plasticity undergoing in the PRL before the training. We also found that the tRNS was able to modulate the visuospatial integration in the early visual processing, promoting plastic changes in the stimulated network. Its effects were not limited to the short-term modulation but also produced a boosting of the learning in a crowding task. The final experiment showed that a combination of tRNS and perceptual training could result in greater improvements and larger transfer to untrained visual tasks in adults with MD than training alone. Overall, our results indicate that tRNS of the visual cortex has potential application as an additional therapy to improve vision in adults with bilateral central blindness.
... Good choices are based solely on information that is relevant to the choice at hand, and rational 444 agents will successfully ignore distracting signals when making decisions (Luce, 1959 part because of a contextual facilitation mechanism at the decision level, akin to that described in 475 sensory circuits (Stemmler et al., 1995), rather than because of an active cost of response 476 ...
When making decisions, humans are often distracted by irrelevant information. Distraction has different impact on perceptual, cognitive and value-guided choices, giving rise to well-described behavioural phenomena such as the tilt illusion, conflict adaptation, or economic decoy effects. However, a single, unified model that can account for all these phenomena has yet to emerge. Here, we offer one such account, based on adaptive gain control, and additionally show that it successfully predicts a range of counterintuitive new behavioural phenomena on variants of a classic cognitive paradigm, the Eriksen flanker task. We also report that BOLD signals in a dorsal network prominently including the anterior cingulate cortex (dACC), index a gain-modulated decision variable predicted by the model. This work unifies the study of distraction across perceptual, cognitive and economic domains.
It is well known that visual cortical neurons respond vigorously to a limited range of stimulus orientations, while their primary afferent inputs, neurons in the lateral geniculate nucleus (LGN), respond well to all orientations. Mechanisms based on intracortical inhibition and/or converging thalamocortical afferents have previously been suggested to underlie the generation of cortical orientation selectivity; however, these models conflict with experimental data. Here, a 1:4 scale model of a 1700 microns by 200 microms region of layer IV of cat primary visual cortex (area 17) is presented to demonstrate that local intracortical excitation may provide the dominant source of orientation-selective input. In agreement with experiment, model cortical cells exhibit sharp orientation selectivity despite receiving strong iso-orientation inhibition, weak cross- orientation inhibition, no shunting inhibition, and weakly tuned thalamocortical excitation. Sharp tuning is provided by recurrent cortical excitation. As this tuning signal arises from the same pool of neurons that it excites, orientation selectivity in the model is shown to be an emergent property of the cortical feedback circuitry. In the model, as in experiment, sharpness of orientation tuning is independent of stimulus contrast and persists with silencing of ON-type subfields. The model also provides a unified account of intracellular and extracellular inhibitory blockade experiments that had previously appeared to conflict over the role of inhibition. It is suggested that intracortical inhibition acts nonspecifically and indirectly to maintain the selectivity of individual neurons by balancing strong intracortical excitation at the columnar level.
Noise in dynamical systems is usually considered a nuisance. But in certain nonlinear systems, including electronic circuits and biological sensory apparatus, the presence of noise can in fact enhance the detection of weak signals. This phenomenon, called stochastic resonance, may find useful application in physical, technological and biomedical contexts.
The intrinsic connections of the cortex have long been known to run vertically, across the cortical layers. In the present study we have found that individual neurons in the cat primary visual cortex can communicate over suprisingly long distances horizontally (up to 4 mm), in directions parallel to the cortical surface. For all of the cells having widespread projections, the collaterals within their axonal fields were distributed in repeating clusters, with an average periodicity of 1 mm. This pattern of extensive clustered projections has been revealed by combining the techniques of intracellular recording and injection of horseradish peroxidase with three-dimensional computer graphic reconstructions. The clustering pattern was most apparent when the cells were rotated to present a view parallel to the cortical surface. The pattern was observed in more than half of the pyramidal and spiny stellate cells in the cortex and was seen in all cortical layers. In our sample, cells made distant connections within their own layer and/or within another layer. The axon of one cell had clusters covering the same area in two layers, and the clusters in the deeper layer were located under those in the upper layer, suggesting a relationship between the clustering phenomenon and columnar cortical architecture. Some pyramidal cells did not project into the white matter, forming intrinsic connections exclusively. Finally, the axonal fields of all our injected cells were asymmetric, extending for greater distances along one cortical axis than along the orthogonal axis. The axons appeared to cover areas of cortex representing a larger part of the visual field than that covered by the excitatory portion of the cell's own receptive field. These connections may be used to generate larger receptive fields or to produce the inhibitory flanks in other cells' receptive fields.
Maps of orientation preference and selectivity, inferred from differential images of orientation (Blasdel, 1992), reveal linear organizations in patches, 0.5-1.0 mm across, where orientation selectivities are high, and where preferred orientations rotate linearly along one axis while remaining constant along the other. Most of these linear zones lie between the centers of adjacent ocular dominance columns, with their short iso-orientation slabs oriented perpendicular, in regions enjoying the greatest binocular overlap. These two-dimensional linear zones are segregated by one- and zero-dimensional discontinuities that are particularly abundant in the centers of ocular dominance columns, and that are also correlated with cytochrome oxidase-rich zones within them. Discontinuities smaller than 90 degrees extend in one dimension, as fractures, while discontinuities greater than 90 degrees are confined to points, in the form of singularities, that are generated when orientation preferences rotate continuously through +/- 180 degrees along circular paths. The continuous rotations through 180 degrees imply that direction preferences are not organized laterally in striate cortex. And they also ensure that preferences for all orientations converge at each singularity, with perpendicular orientations represented uniquely close together on opposite sides. The periodic interspersing of linear zones and singularities suggests that orientation preferences are organized by at least two competing schemes. They are optimized for linearity, along with selectivity and binocularity, in the linear zones, and they are optimized for density near singularities. Since upper-layer neurons are likely to have similarly sized dendritic fields in all regions (Lund and Yoshioka, 1991), those in the linear zones should receive precise information about narrowly constrained orientations, while those near singularities should receive coarse information about all orientations--very different inputs that suggest different perceptual functions.
1. We have studied in vivo the intracellular responses of neurones in cat visual cortex to electrical pulse stimulation of the cortical afferents and have developed a microcircuit that simulates much of the experimental data. 2. Inhibition and excitation are not separable events, because individual neurones are embedded in microcircuits that contribute strong population effects. Synchronous electrical activation of the cortex inevitably set in motion a sequence of excitation and inhibition in every neurone we recorded. The temporal form of this response depends on the cortical layer in which the neurone is located. Superficial layer (layers 2+3) pyramidal neurones show a more marked polysynaptic excitatory phase than the pyramids of the deep layers (layers 5+6). 3. Excitatory effects on pyramidal neurones, particularly the superficial layer pyramids, are in general not due to monosynaptic input from thalamus, but polysynaptic input from cortical pyramids. Since the thalamic input is transient it does not provide the major, sustained excitation arriving at any cortical neurone. Instead the intracortical excitatory connections provide the major component of the excitation. 4. The polysynaptic excitatory response would be sustained well after the stimulus, were it not for the suppressive effect of intracortical inhibition induced by the pulse stimulation. 5. Intracellular recording combined with ionophoresis of gamma-aminobutyric acid (GABA) agonists and antagonists showed that intracortical inhibition is mediated by GABAA and GABAB receptors. The GABAA component occurs in the early phase of the impulse response. It is reflected in the strong hyperpolarization that follows the excitatory response and lasts about 50 ms. The GABAB component occurs in the late phase of the response, and is reflected in a sustained hyperpolarization that lasts some 200-300 ms. Both components are seen in all cortical pyramidal neurones. However, the GABAA component appears more powerful in deep layer pyramids than superficial layer pyramids. 6. The microcircuit simulates with good fidelity the above data from experiments in vivo and provides a novel explantation for the apparent lack of significant inhibition during visual stimulation. The basic circuit may be common to all cortical areas studied and thus the microcircuit may be a 'canonical' microcircuit for neocortex.
Slices of sensorimotor and anterior cingulate cortex from guinea pigs were maintained in vitro and bathed in a normal physiological medium. Electrophysiological properties of neurons were assessed with intracellular recording techniques. Some neurons were identified morphologically by intracellular injection of the fluorescent dye Lucifer yellow CH. Three distinct neuronal classes of electrophysiological behavior were observed; these were termed regular spiking, bursting, and fast spiking. The physiological properties of neurons from sensorimotor and anterior cingulate areas did not differ significantly. Regular-spiking cells were characterized by action potentials with a mean duration of 0.80 ms at one-half amplitude, a ratio of maximum rate of spike rise to maximum rate of fall of 4.12, and a prominent afterhyperpolarization following a train of spikes. The primary slope of initial spike frequency versus injected current intensity was 241 Hz/nA. During prolonged suprathreshold current pulses the frequency of firing adapted strongly. When local synaptic pathways were activated, all cells were transiently excited and then strongly inhibited. Bursting cells were distinguished by their ability to generate endogenous, all-or-none bursts of three to five action potentials. Their properties were otherwise very similar to regular-spiking cells. The ability to generate a burst was eliminated when the membrane was depolarized to near the firing threshold with tonic current. By contrast, hyperpolarization of regular-spiking (i.e., nonbursting) cells did not uncover latent bursting tendencies. The action potentials of fast-spiking cells were much briefer (mean of 0.32 ms) than those of the other cell types.(ABSTRACT TRUNCATED AT 250 WORDS)
1. Computer simulations were used to study the effect of volt- age-dependent calcium and potassium conductances in the apical dendritic tree of a pyramidal cell on the synaptic efficacy of apical synaptic input. The apical tuft in layers 1 and 2 is the target of feedback projections from other cortical areas. 2. The current, Jsoma, flowing into the soma in response to syn- aptic input was used to assess synaptic efficacy. This measure takes full account of all the relevant nonlinearities in the dendrites and can be used during spiking activity. Isorna emphasizes current flow- ing in response to synaptic input rather than synaptically induced voltage change. This measure also permits explicit characteriza- tion of the input-output relationship of the entire neuron by com- puting the relationship between presynaptic input and postsynap- tic output frequency. 3. Simulations were based on two models. The first was a bio- physically detailed 400-compartment model of a morphologically characterized layer 5 pyramidal cell from striate cortex of an adult cat. In this model eight voltage-dependent conductances were in- corporated into the somatic membrane to provide the observed firing behavior of a regular spiking cell. The second model was a highly simplified three-compartment equivalent electrical circuit. 4. If the dendritic tree is entirely passive, excitatory synaptic input of the non-N-methyl-D-aspartate (non-NMDA) type to layers 1, 2, and 3 saturate at very moderate input rates, because of the high input impedance of the apical tuft. Layers 1 and 2 to- gether can deliver only 0.25 nA current to the soma. This modest effect is surprising in view of the important afferents that synapse on the apical tuft and is inconsistent with experimental data indi- cating a more powerful effect. 5. We introduced in a controlled manner a voltage-dependent potassium conductance in the apical tuft, gk, to prevent satura- tion of the synaptic response. This conductance was designed to linearize the relationship between presynaptic input frequency and the somatic current. We also introduced a voltage-dependent calcium conductance along the apical trunk, gca, to amplify the apical signal, i.e., the synaptic current reaching the soma. 6. To arrive at a specific relationship between the presynaptic input rate and the somatic current delivered by the synaptic input, we derived the activation curves of gk and gca either analytically or numerically. The resultant voltage-dependent behavior of both conductances was similar to experimentally measured activation curves. 7. We propose that the apical tuft represents a separate integra- tive region that is coupled to the soma by a current amplifier in the apical dendrite. The gain of the amplifier can be controlled by modulating the properties of either gca or gk.
1. We recorded responses from neurons in area V1 of the alert macaque monkey to textured patterns modeled after stimuli used in psychophysical experiments of pop-out. Neuronal responses to a single oriented line segment placed within a cell's classical receptive field (CRF) were compared with responses in which the center element was surrounded by rings of elements placed entirely outside the CRF. The orientations of the surround elements either matched the center element, were orthogonal to it, or were random. 2. The addition of the textured surround tended to suppress the response to the center element by an average of 34%. Overall, almost 80% of the 122 cells analyzed in detail were significantly suppressed by at least one of the texture surrounds. 3. Cells tended to respond more strongly to a stimulus in which there was a contrast in orientation between the center and surround than to a stimulus lacking such contrast. The average difference was 9% of the response to the optimally oriented center element alone. For the 32% of the cells showing a statistically significant orientation contrast effect, the average difference was 28%. 4. Both the general suppression and orientation contrast effects originated from surround regions at the ends of the center bar as well as regions along the sides of the center bar. 5. The amount of suppression induced by the texture surround decreased as the density of the texture elements decreased. 6. Both the general suppression and the orientation contrast effects appeared early in the population response to the stimuli. The general suppression effect took approximately 7 ms to develop, whereas the orientation contrast effect took 18-20 ms to develop. 7. These results are consistent with a possible functional role of V1 cells in the mediation of perceptual pop-out and in the segregation of texture borders. Possible anatomic substrates of the effects are discussed.
We have discussed several results that lead to a view that cells in the visual system are endowed with dynamic properties, influenced by context, expectation, and long-term modifications of the cortical network. These observations will be important for understanding how neuronal ensembles produce a system that perceives, remembers, and adapts to injury. The advantage to being able to observe changes at early stages in a sensory pathway is that one may be able to understand the way in which neuronal ensembles encode and represent images at the level of their receptive field properties, of cortical topographies, and of the patterns of connections between cells participating in a network.