An emotional-perceptual-memory circuit in the human brain. The amygdala (red), an anterior medial temporal lobe structure, is a crucial structure in registering emotional occurrences. Extensive connection (arrows) to visual cortex (orange) and hippocampus (blue) allows amygdala to modulate their function and facilitate perceptual and memory functions in those regions. 

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... as evident in their global effects on virtually all aspects of cognition. This is exemplified in the fact that when we are sad the world seems less bright, we struggle to concentrate, and we become selective in what we recall. These latter aspects of emotion and their influences on other psychological functions are ad- dressed here. An evolutionary perspective on emotion suggests that environmental events of value should be susceptible to preferential perceptual processing. One means of achieving this is by emotion enhancing attention, leading to increased detection of emotional events. The influence of emotion on attention can be studied in classic visual search and spatial orienting tasks. In a visual search, the standard finding is that the time taken to detect a specified target increases in direct proportion to the number of irrelevant distracters, indi- cating serial attentive processing. However, for emotional stimuli there is more rapid target detection for faces with positive or negative expressions, or for spiders or snakes, with the most consistent capture of attention being evident for fear-relevant stimuli ( 3 ). Similar effects are seen in spatial orienting tasks where there is a faster response to targets appearing on the same side as an emotional cue (e.g., faces, spiders, threat words, conditioned shapes) and a slower response to those appearing on the opposite side ( 4 , 5 ). Neuroimaging data, using spatial orienting paradigms, point to orbital prefrontal cortex as a possible site of interaction ( 4 ). The “capture of attention” is not the sole means by which emotional stimuli influence perception, and emerging evidence indicates mechanisms independent of attention. Per- ceptual processing under conditions of limited attention as, for example, processing of stimuli at unattended spatial locations is often referred to as preattentive. In visual backward masking paradigms, a briefly presented (ms) target can be rendered invisible if immediate- ly followed by a second “masking stimulus.” In situations where the hidden target stimulus is an emotional item, for example a conditioned angry face or a spider, preserved processing can be indexed by differential skin conductance responses (SCRs) to fear-relevant compared with fear-irrelevant targets, even though the target stimulus is not per- ceived ( 6 ). Similar findings are evident using the attentional blink paradigm. This refers to a situation where detection of an initial target stimulus in a visual stimulus stream leads to impaired awareness, or “inattentional blind- ness,” for a successive second target. This inattentional blindness is greatly diminished where a second target is an emotional item ( 7 ). This finding suggests an advantage in detection of an emotional item even in cir- cumstances where attentional resources are limited. Studies of patients with focal brain lesions provide additional evidence for independence of emotional processing from attentional mechanisms. After brain damage to right inferior parietal cortex, patients frequently fail to perceive a stimulus presented in their contralesional hemifield (spatial neglect) or, in milder forms, fail to perceive a stimulus when a simul- taneous stimulus is presented on the ipsilesional side (sensory extinction). This contralesional deficit is greatly attenuated for emotional stimuli, such as faces with happy or angry expressions ( 8 ) or images of spiders ( 9 ). Noncon scious processing of emotion has also been demonstrated in the blindfield of patients with damage to primary visual cortex ( 10 ). These findings indicate processing of emotional stimuli occurs before the operation of selective attention and such “ preattentive processing ” results in enhanced stimulus detection. Pre-attentive processing of emotional stimuli, such as faces, implies an early discrimination between the occurrence of emotional and nonemotional events. Using magneto-encephalography (MEG), dis- criminatory responses to emotional faces are seen in midline occipital cortex as early as 100 to 120 ms after stimulus onset, before the onset of a characteristic face-related response at approximately 170 ms ( 11 , 12 ). Intermodal bind- ing of emotion for presentation of anger in voice and face is associated with a distinct electroencephalographic potential occurring at about 100 ms ( 13 ). Short-latency responses (120 to 160 ms) to aversive stimulus presentation are also seen during direct intracerebral recordings within ventral prefrontal cortex ( 14 ). Thus, electrophysiological data point to rapid and widespread neuronal responses to emotional stimuli that precede responses associated with actual stimulus identification which occur at approximately 170 ms after stimulus onset. An important neurobiological question is how processing of emotional stimuli pro- ceeds in the absence of attention. Accumu- lating evidence points to the amygdala as an important mediator of emotional influences on perception (Fig. 1). In functional neuroimaging experiments using visual backward masking paradigms, where emotional stimuli are presented out of awareness, an amygdala response discriminates between unseen emotional and unseen nonemotional targets ( 15 , 16 ). In other experiments with overt stimulus presentation but where attention is systematically manipu- lated, an amygdala response to fearful faces is independent of the concurrent focus of attention ( 17 ). Studies involving patients with either blindsight or visual extinction demonstrate an amygdala response to emotional stimuli presented out of awareness in the damaged hemifield ( 18 , 19 ). Residual processing abilities for unaware emotional stimulus presentation are associated with engagement of a subcortical retino-collicu- lar-pulvinar pathway specific to unaware emotional stimulus processing ( 15 , 18 ). The involvement of this pathway is of considerable interest, because it is also implicated in residual visual processing evident in patients with blindsight. One suggestion is that certain classes of emotional stimuli, for example coarse visual cues present in fearful faces, can be processed by a noncortical pathway to enable rapid adaptive responses to dan- ger ( 20 ). A related neurobiological question is how preattentive processing of emotional events influences, and indeed enhances, perception. One possibility is that inputs from emotional processing regions, in particular the amygdala, modulate the function of regions involved in early object perceptual processing. Anatomically, the amygdala receives visual inputs from ventral visual pathways and sends feedback projections to all processing stages within this pathway ( 21 ). Neuroimaging data provide evidence for context-dependent enhancement of functional connectivity between amygdala and extrastriate visual regions expressed during processing of an emotional visual input ( 22 , 23 ). There is now evidence showing this connectivity has psychological consequences in that after amygdala damage a visual perceptual enhancement for emotional items is abolished ( 7 ). Privileged perceptual processing of emotional events provide a means of not only index- ing occurrences of value but facilitating their availability to other cognitive domains. The cognitive domain where the influence of emotion is best understood is memory. Enhanced memory for events of value allow better predictions regarding biologically important occurrences when re-encountering similar events in the future. The best example is seen in classical conditioning, which provides an inflexible, ubiquitously expressed form of emotional memory. In simple terms, this form of memory describes a situation where a neutral stimulus, through pairing in temporal contiguity with an emotional stimulus (for example, an aversive noise in fear conditioning), acquires an ability to predict future occurrences of this emotional event. From a human behavioral perspective, the importance of this form of memory is that it provides a potential link between a psychological mechanism and psychopathological conditions, such as phobias and post-traumat- ic stress disorder (PTSD). Studies demonstrate that human amygdala is critical for fear conditioning, a form of implicit memory. Patients with amygdala damage do not acquire conditioned fear responses despite retaining explicit knowledge regarding the conditioned (CS) and uncondi- tioned stimulus (UCS) associations ( 24 ). In contrast, patients with hippocampal damage and intact amygdala preserve fear conditioning despite being unable to demonstrate explicit knowledge regarding CS-UCS contin- gencies ( 25 ). Functional neuroimaging experiments also confirm the importance of the amygdala for learning of CS-UCS associations but point to a time-limited role for this structure ( 26 , 27 ). Evidence that the role of the amygdala during emotional learning may be time-limited could indicate that more enduring memory effects are expressed else- where in the brain. Although there is an emphasis on the role of the amygdala in human fear conditioning studies, evidence indicates that it supports other forms of asso- ciative learning, including reward and appet- itive learning ( 28 , 29 ). Enhanced autobiographical or explicit memory for emotional events is well docu- mented in anecdotal accounts of enhanced recollection for events such as the assassina- tion of President Kennedy or the Challenger shuttle disaster. The benefit of emotion on episodic memory function is confirmed in numerous studies showing mnemonic enhancement for material that encompasses personal autobiographical, picture-, and word-based items ( 30 , 31 ), an effect most pronounced in free recall tasks. An enhanced memory for emotional items is also reported in amnesiacs, who despite profound deficits in episodic memory show normal memory enhancement for emotional material when tested by recognition ( 32 ). A striking feature of the biology of emotional ...