The human amygdala plays an important role in gaze monitoring. A PET study

Neural correlates of facial affect processing in children and adolescents with autism spectrum disorder

OBJECTIVE

To examine the neural basis of impairments in interpreting facial emotions in children and adolescents with autism spectrum disorders (ASD).

METHOD

Twelve children and adolescents with ASD and 12 typically developing (TD) controls matched faces by emotion and assigned a label to facial expressions while undergoing functional magnetic resonance imaging.

RESULTS

Both groups engaged similar neural networks during facial emotion processing, including activity in the fusiform gyrus (FG) and prefrontal cortex. However, between-group analyses in regions of interest revealed that when matching facial expressions, the ASD group showed significantly less activity than the TD group in the FG, but reliably greater activity in the precuneus. During the labeling of facial emotions, no between-group differences were observed at the behavioral or neural level. Furthermore, activity in the amygdala was moderated by task demands in the TD group but not in the ASD group.

CONCLUSIONS

These findings suggest that children and adolescents with ASD in part recruit different neural networks and rely on different strategies when processing facial emotions. High-functioning individuals with ASD may be relatively unimpaired in the cognitive assessment of basic emotions, yet still show differences in the automatic processing of facial expressions.

The amygdala and development of the social brain

The amygdala comprises part of an extended network of neural circuits that are critically involved in the processing of socially salient stimuli. Such stimuli may be explicitly social, such as facial expressions, or they may be only tangentially social, such as abstract shapes moving with apparent intention relative to one another. The coordinated interplay between neural activity in the amygdala and other brain regions, especially the medial prefrontal cortex, the occipitofrontal cortex, the fusiform gyrus, and the superior temporal sulcus, allows us to develop social responses and to engage in social behaviors appropriate to our species. The harmonious functioning of this integrated social cognitive network may be disrupted by congenital or acquired lesions, by genetic anomalies, and by exceptional early experiences. Each form of disruption is associated with a slightly different outcome, dependent on the timing of the experience, the location of the lesion, or the nature of the genetic anomaly. Studies in both humans and primates concur; the dysregulation of basic emotions, especially the processing of fear and anger, is an almost invariable consequence of such disruption. These, in turn, have direct or indirect consequences for social behavior.

Reflexive orienting in response to eye gaze and an arrow in children with and without autism

BACKGROUND

This study investigated whether another person's social attention, specifically the direction of their eye gaze, and a non-social directional cue, an arrow, triggered reflexive orienting in children with and without autism in an experimental situation.

METHODS

Children with autism and typically developed children participated in one of two experiments. Both experiments involved the localization of a target that appeared to the left or right of the fixation point. Before the target appeared, the participant's attention was cued to the left or right by either an arrow or the direction of eye gaze on a computerized face.

RESULTS

Children with autism were slower to respond, which suggests a slight difference in the general cognitive ability of the groups. In Experiment 1, although the participants were instructed to disregard the cue and the target was correctly cued in only 50% of the trials, both groups of children responded significantly faster to cued targets than to uncued targets, regardless of the cue. In Experiment 2, children were instructed to attend to the direction opposite that of the cues and the target was correctly cued in only 20% of the trials. Typically developed children located targets cued by eye gaze more quickly, while the arrow cue did not trigger such reflexive orienting in these children. However, both social and non-social cues shifted attention to the cued location in children with autism.

CONCLUSION

These results indicate that eye gaze attracted attention more effectively than the arrow in typically developed children, while children with autism shifted their attention equally in response to eye gaze and arrow direction, failing to show preferential sensitivity to the social cue. Difficulty in shifting controlled attention to the instructed side was also found in children with autism.

Attention orienting by another's gaze direction in children with autism

BACKGROUND

The aim of this study was to investigate attention orienting triggered by another's gaze direction in autism.

METHOD

Twelve high-functioning children with autism and gender- and age-matched normal control children were studied using two tasks. In the first task, children were asked to detect laterally presented target stimuli preceded by centrally presented facial cue stimuli in which gaze was either straight ahead or averted. The direction of the cue was either congruent, neutral, or incongruent with respect to the laterality of the target stimulus. In the second task, children were asked to discriminate the direction of eye gaze.

RESULTS

The results showed that another person's static gaze direction triggered an automatic shift of visual attention, both in children with autism and in normally developing children. The children in both groups were also able to overtly discriminate the direction of the gaze.

CONCLUSION

These results seem to suggest that, in children with autism, the visual system processes information about another person's gaze direction and sends this information to those areas that subserve reflexive attention orienting. However, future studies are needed to investigate whether the processing of eyes and gaze direction relies on similar neural mechanisms in children with autism and in normally developing children.

Dissociable neural pathways for the perception and recognition of expressive and instrumental gestures

Previous functional imaging studies have sought to characterize the neural correlates of gesture representation. However, little is yet known about the representation of different categories of gesture. Here we contrasted the perception of hand gestures that express inner feeling states, e.g. I am angry, I do not care, with the perception of instrumental gestures intended to change the behavior of others by communicating commands, e.g. come here, look over there. We hypothesised that recognition of expressive gestures would activate a network of brain regions associated with mentalising ('theory of mind') whereas instrumental gestures would activate different neural pathways. Twelve normal volunteers underwent fMRI while they watched a series of short videos (3 s duration) of actors performing expressive and instrumental gestures. The volunteers had either to recognise the gesture or to monitor the positions of the hands. As predicted, different neural networks were activated by the observation of instrumental or expressive gestures. The perception of expressive gestures elicited activity in the anterior paracingulate cortex, the amygdala and the temporal poles bilaterally and the right superior temporal sulcus. These regions have all previously been activated during the performance of mentalising tasks. In contrast, instrumental gestures elicited activity in a left-lateralised system previously associated with language and motor imitation.

Neurobiology of emotion perception I: The neural basis of normal emotion perception

There is at present limited understanding of the neurobiological basis of the different processes underlying emotion perception. We have aimed to identify potential neural correlates of three processes suggested by appraisalist theories as important for emotion perception: 1) the identification of the emotional significance of a stimulus; 2) the production of an affective state in response to 1; and 3) the regulation of the affective state. In a critical review, we have examined findings from recent animal, human lesion, and functional neuroimaging studies. Findings from these studies indicate that these processes may be dependent upon the functioning of two neural systems: a ventral system, including the amygdala, insula, ventral striatum, and ventral regions of the anterior cingulate gyrus and prefrontal cortex, predominantly important for processes 1 and 2 and automatic regulation of emotional responses; and a dorsal system, including the hippocampus and dorsal regions of anterior cingulate gyrus and prefrontal cortex, predominantly important for process 3. We suggest that the extent to which a stimulus is identified as emotive and is associated with the production of an affective state may be dependent upon levels of activity within these two neural systems.

Effect of head orientation on gaze processing in fusiform gyrus and superior temporal sulcus

We used functional MRI with an event-related design to dissociate the brain activation in the fusiform gyrus (FG) and posterior superior temporal sulcus (STS) for multiple face and gaze orientations. The event-related design allowed for concurrent behavioral analysis, which revealed a significant effect of both head and gaze orientation on the speed of gaze processing, with the face and gaze forward condition showing the fastest reaction times. In conjunction with this behavioral finding, the FG responded with the greatest activation to face and gaze forward, perhaps reflecting the unambiguous social salience of congruent face and gaze directed toward the viewer. Random effects analysis showed greater activation in both the FG and posterior STS when the subjects viewed a direct face compared to an angled face, regardless of gaze direction. Additionally, the FG showed greater activation for forward gaze compared to angled gaze, but only when the face was forward. Together, these findings suggest that head orientation has a significant effect on gaze processing and these effects are manifest not only in the STS, but also the FG.

Annotation: the neural basis of social impairments in autism: the role of the dorsal medial-frontal cortex and anterior cingulate system

BACKGROUND

The fundamental social disturbance of autism is characterized, in part, by problems in the acquisition of joint attention skills in the first years of life, followed by impairments in the development of social cognition, as assessed on theory of mind (ToM) measures. Recently, studies have indicated that a system involving the dorsal medial-frontal cortex (DMFC), and the anterior cingulate (AC), may contribute to the development of the tendency to initiate joint attention in infancy. Similarly, research has implicated the DMFC/AC system in ToM performance in typical and atypical individuals. These data suggest it may be useful to consider the functions associated with this system in the developmental psychopathology of autism.

METHOD

A review of the studies of the connections between the DMFC/AC system, joint attention and ToM task performance.

RESULTS AND CONCLUSIONS

This review raises the hypothesis that the DMFC/AC may be involved in the basic disturbance in social orienting in autism. The DMFAC/AC may also play a role in the capacity to monitor proprioceptive information concerning self-action and integrate this self-related information with exteroceptive perceptual information about the behavior of other people. A disturbance in these functions of the DMFC/ AC may contribute to the atypical development of intersubjectivity, joint attention and social cognition that may impair the lives of people with autism. Thus, impairment in the development of this system may constitute a neural substrate for socio-cognitive deficits in autism.

Brain networks for analyzing eye gaze

The eyes convey a wealth of information in social interactions. This information is analyzed by multiple brain networks, which we identified using functional magnetic resonance imaging (MRI). Subjects attempted to detect a particular directional cue provided either by gaze changes on an image of a face or by an arrow presented alone or by an arrow superimposed on the face. Another control condition was included in which the eyes moved without providing meaningful directional information. Activation of the superior temporal sulcus accompanied extracting directional information from gaze relative to directional information from an arrow and relative to eye motion without relevant directional information. Such selectivity for gaze processing was not observed in face-responsive fusiform regions. Brain activations were also investigated while subjects viewed the same face but attempted to detect when the eyes gazed directly at them. Most notably, amygdala activation was greater during periods when direct gaze never occurred than during periods when direct gaze occurred on 40% of the trials. In summary, our results suggest that increases in neural processing in the amygdala facilitate the analysis of gaze cues when a person is actively monitoring for emotional gaze events, whereas increases in neural processing in the superior temporal sulcus support the analysis of gaze cues that provide socially meaningful spatial information.

Interpreting gaze in Turner syndrome: impaired sensitivity to intention and emotion, but preservation of social cueing

Women with Turner's syndrome (TS), who lack a complete X-chromosome, show an impairment in remembering faces and in classifying "fear" in face images. Could their difficulties extend to the processing of gaze? Three tasks, all of which rely on the ability to make use of the eye-region of a pictured face, are reported. Women with TS were impaired at judging mental state from images of the upper face ("reading the mind in the eyes"). They were also specifically impaired at interpreting "fear" from displays of the eye-region of the face. However, they showed normal susceptibility to direction of gaze as an attentional cue (social cueing), since they were as sensitive as controls to the validity of the cue, under conditions where it should be ignored. In this task, unlike those of reading the upper face for intention or expression, PIQ accounted for a significant amount of individual variance in task performance. The processing of displays of the eye region affording social and affective information is specifically affected in TS. We speculate that amygdala dysfunction is likely to be implicated in this anomalous behaviour. The presence in the female karyotype of two complete X-chromosomes is protective for some socio-cognitive abilities related to the modulation of behaviour by the interpretation of gaze.

Facial expressions of emotion: a cognitive neuroscience perspective

Facial expressions are one example of emotional behavior that illustrate the importance of emotions to both basic survival and social interaction. Basic facial responses to stimuli such as sweet and bitter taste are important for species fitness and governed by simple rules. Even at this basic level, facial responses have communicative value to other species members. During evolution simple facial responses were extended for use in more complex nonverbal communications; the responses are labile. The perception and production of facial expressions are cognitive processes and numerous subcortical and cortical areas contribute to these operations. We suggest that no specific emotion center exists over and above cognitive systems in the brain, and that emotion should not be divorced from cognition.

Fear Recognition and the Neural Basis of Social Cognition

Recent developments in cognitive neuroscience and neurobiology emphasise the interface between our emotions, our feelings and our ability to interact appropriately in social situations. The neural basis of social cognition is subject to intensive research in both humans and non-human primates, research that is providing exciting, provocative and yet consistent findings. Centre stage is the role of efferent and afferent connectivity between the amygdala and neocortical brain regions, now believed to be critical for the processing of social information. Recent research suggests that a sub-cortical neural pathway, routed through the amygdala, may turn out to be a key player in the mystery of why humans are so prone to disorders of social cognition. This pathway responds to direct eye contact, one of many classes of potential threat. In humans, arousal evoked by this exquisitely social stimulus is modulated and controlled by a variety of specific cortical regions. Neural circuits that evolved for the purpose of fear detection in other's faces, an essentially threatening stimulus, are now associated with the acquisition of social skills and appropriate responsiveness in social encounters.

Is the human amygdala specialized for processing social information?

A number of studies in humans and other animals has confirmed the amygdala's role in modulating cognition and behavior on the basis of a stimulus' motivational, emotional, and social attributes. This raises the question of how these attributes are related: is social information processing reducible to motivational processing? Some recent data suggest the possibility that the amygdala's primitive function may be motivational processing that is domain-general, but that its function in primates, and especially humans, may have evolved to process social information specifically. While the issue is unresolved, future experiments could provide additional support.

Acquired theory of mind impairments in individuals with bilateral amygdala lesions

Studies in humans suggest that the amygdala plays a role in processing social information. A key component of social information processing is what developmental psychologists call "theory of mind": the ability to infer others' mental states. Recent studies have raised the possibility that the amygdala is involved in theory of mind, showing amygdala activation during a theory of mind task, or showing impairment on theory of mind tasks in a patient with amygdala damage acquired in childhood. Here, we present the first evidence of theory of mind deficits following amygdala damage acquired in adulthood. Two participants, D.R. and S.E., with acquired bilateral amygdala damage showed difficulties with two theory of mind tasks, "Recognition of Faux Pas" (for D.R., z=-5.17; for S.E., z=-1.83) and "Reading the Mind in the Eyes" (for S.E., z=-1.91; for D.R., z=-1.4). The items on which D.R. and S.E. made errors on these tasks were uncorrelated with the items that control participants found most difficult, indicating that these deficits cannot be attributed solely to the cognitive difficulty of the tasks. These results indicate that the amygdala's critical role in theory of mind may not be just in development, but also in "on-line" theory of mind processing in the adult brain.

Brain activation evoked by perception of gaze shifts: the influence of context

Prior studies from our laboratory [Journal of Neuroscience 18 (1998) 2188; Cognitive Neuropsychology 17 (2000) 221] have demonstrated that discrete regions of the superior temporal sulcus (STS) are activated when a subject views a face in which the eyes shift their gaze. Here we investigated the degree to which activity in the STS and other brain regions is modulated by the context of the perceived gaze shift; that is, when the shift correctly or incorrectly acquires a visual target. Fifteen subjects participated in an event-related functional magnetic resonance imaging experiment in which they viewed an animated face that remained present throughout each run. On each of 21 trials within each run, a small checkerboard appeared and flickered at one of six locations within the character's visual field. On "correct" trials, the character shifted its gaze towards the checkerboard after a delay of 1 or 3s. On "incorrect" trials, the character shifted its gaze towards empty space after the same delays. On "no shift" trials, the character's eyes did not move. Significantly larger hemodynamic responses (HDR) were evoked by gaze shifts compared to no gaze shifts in primarily right hemisphere STS. The gaze-evoked HDR was significantly delayed in peak amplitude for 3s compared to 1s shifts. For 1s shifts, a strong effect of context was observed in which errors evoked a HDR with extended duration. Although this study focused upon STS, similar effects were also observed in the intraparietal sulcus and fusiform gyrus.

Being the target of another's emotion: a PET study

The eye region and gaze behaviour are known to play a major role in conveying information about direction of attention and emotional dispositions. Positron emission tomography scanning was used to explore the cerebral structures involved while subjects were asked to attribute hostile or friendly intentions to video-taped actors who directed attention towards or away from the subjects. As expected, a number of brain regions known to be involved in emotion processing was found activated when subjects had to attribute an emotion regardless of gaze direction. In addition, results indicate that gaze direction has an impact on the brain regions recruited to interpret emotions. The anterior region of the superior temporal gyrus (STG) was selectively activated during analysis of emotions through eye contact. This result provides neurophysiological evidence for privileged processing when an individual becomes personally involved as the object of another's emotions.

Functional imaging of 'theory of mind'

Our ability to explain and predict other people's behaviour by attributing to them independent mental states, such as beliefs and desires, is known as having a 'theory of mind'. Interest in this very human ability has engendered a growing body of evidence concerning its evolution and development and the biological basis of the mechanisms underpinning it. Functional imaging has played a key role in seeking to isolate brain regions specific to this ability. Three areas are consistently activated in association with theory of mind. These are the anterior paracingulate cortex, the superior temporal sulci and the temporal poles bilaterally. This review discusses the functional significance of each of these areas within a social cognitive network.

Dissociable neural pathways are involved in the recognition of emotion in static and dynamic facial expressions

Facial expressions of emotion powerfully influence social behavior. The distributed network of brain regions thought to decode these social signals has been empirically defined using static, usually photographic, displays of such expressions. Facial emotional expressions are however highly dynamic signals that encode the emotion message in facial action patterns. This study sought to determine whether the encoding of facial expressions of emotion by static or dynamic displays is associated with different neural correlates for their decoding. We used positron emission tomography to compare patterns of brain activity in healthy men and women during the explicit judgment of emotion intensity in static and dynamic facial expressions of anger and happiness. Compared to judgments of spatial orientation for moving neutral facial expressions, the judgment of anger in dynamic expressions was associated with increased right-lateralized activity in the medial, superior, middle, and inferior frontal cortex and cerebellum, while judgments of happiness were associated with relative activation of the cuneus, temporal cortex, and the middle, medial, and superior frontal cortex. In contrast, the perception of anger or happiness in static facial expressions activated a motor, prefrontal, and parietal cortical network previously shown to be involved in motor imagery. The direct contrast of dynamic and static expressions indicated differential activation of visual area V5, superior temporal sulcus, periamygdaloid cortex, and cerebellum for dynamic angry expressions and differential activation of area V5, extrastriate cortex, brain stem, and middle temporal cortical activations for dynamic happy expressions. Thus, a distribution of neural activations is related to the analysis of emotion messages in the nearly constant biological motion of the face and differ for angry and happy expressions. Static displays of facial emotional expression may represent noncanonical stimuli that are processed for emotion content by mental strategies and neural events distinct from their more ecologically relevant dynamic counterparts.

Are you looking at me? Accuracy in processing line-of-sight in Turner syndrome

The behavioural phenotype of women with Turner syndrome (X-monosomy, 45,X) is poorly understood, but includes reports of some social development anomalies. With this in mind, accuracy of direction of gaze detection was investigated in women with Turner syndrome. Two simple experimental tasks were used to test the prediction that the ability to ascertain gaze direction from face photographs showing small lateral angular gaze deviations would be impaired in this syndrome, compared with a control population of men and women. The prediction was confirmed and was found to affect both the detection of egocentric gaze from the eyes ('is the face looking at me?') and the detection of allocentric gaze, where the eyes in a photographed face inspected one of a number of locations of attention ('where is she looking?'). We suggest that dosage-sensitive X-linked genes contribute to the development of gaze-monitoring abilities.

Neural response to emotional faces with and without awareness: event-related fMRI in a parietal patient with visual extinction and spatial neglect

This study examined whether differential neural responses are evoked by emotional stimuli with and without conscious perception, in a patient with visual neglect and extinction. Stimuli were briefly shown in either right, left, or both fields during event-related fMRI. On bilateral trials, either a fearful or neutral left face appeared with a right house, and it could either be extinguished from awareness or perceived. Seen faces in left visual field (LVF) activated primary visual cortex in the damaged right-hemisphere and bilateral fusiform gyri. Extinguished left faces increased activity in striate and extrastriate cortex, compared with right houses only. Critically, fearful faces activated the left amygdala and extrastriate cortex both when seen and when extinguished; as well as bilateral orbitofrontal and intact right superior parietal areas. Comparison of perceived versus extinguished faces revealed no difference in amygdala for fearful faces. Conscious perception increased activity in fusiform, parietal and prefrontal areas of the left-hemisphere, irrespective of emotional expression; while a differential emotional response to fearful faces occurring specifically with awareness was found in bilateral parietal, temporal, and frontal areas. These results demonstrate that amygdala and orbitofrontal cortex can be activated by emotional stimuli even without awareness after parietal damage; and that substantial unconscious residual processing can occur within spared brain areas well beyond visual cortex, despite neglect and extinction.

Reading the mind from eye gaze

Baron-Cohen [Mindblindness: an essay on autism and theory of mind. Cambridge, MA: MIT Press, 1997] has suggested that the interpretation of gaze plays an important role in a normal functioning theory of mind (ToM) system. Consistent with this suggestion, functional imaging research has shown that both ToM tasks and eye gaze processing engage a similar region of the posterior superior temporal sulcus (STS). However, a second brain region associated with ToM, the medial prefrontal (MPF) cortex, has not been identified by previous eye gaze studies. We discuss the methodological issues that may account for the absence of MPF activation in these experiments and present a PET study that controls for these factors. Our experiment included three conditions in which the proportions of faces gazing at, and away from, the participant, were as follows: 100% direct [0% averted], 50% direct-50% averted, and 100% horizontally averted [0% direct]. Two control conditions were also included in which the faces' gaze were averted down, or their eyes were closed. Contrasts comparing the gaze conditions with each of the control conditions revealed medial frontal involvement. Parametric analyses showed a significant linear relationship between increasing proportions of horizontally averted gaze and increased rCBF in the MPF cortex. The opposite parametric analysis (increasing proportions of direct gaze) was associated with increased rCBF in a number of areas including the superior and medial temporal gyri. Additional subtraction contrasts largely confirmed these patterns. Our results demonstrate a considerable degree of overlap between the medial frontal areas involved in eye gaze processing and theory of mind tasks.

Are you looking at me? Eye gaze and person perception

Previous research has highlighted the pivotal role played by gaze detection and interpretation in the development of social cognition. Extending work of this kind, the present research investigated the effects of eye gaze on basic aspects of the person-perception process, namely, person construal and the extraction of category-related knowledge from semantic memory. It was anticipated that gaze direction would moderate the efficiency of the mental operations through which these social-cognitive products are generated. Specifically, eye gaze was expected to influence both the speed with which targets could be categorized as men and women and the rate at which associated stereotypic material could be accessed from semantic memory. The results of two experiments supported these predictions: Targets with nondeviated (i.e., direct) eye gaze elicited facilitated categorical responses. The implications of these findings for recent treatments of person perception are considered.

Human neural systems for face recognition and social communication

Face perception is mediated by a distributed neural system in humans that consists of multiple, bilateral regions. The functional organization of this system embodies a distinction between the representation of invariant aspects of faces, which is the basis for recognizing individuals, and the representation of changeable aspects, such as eye gaze, expression, and lip movement, which underlies the perception of information that facilitates social communication. The system also has a hierarchical organization. A core system, consisting of occipitotemporal regions in extrastriate visual cortex, mediates the visual analysis of faces. An extended system consists of regions from neural systems for other cognitive functions that can act in concert with the core system to extract meaning from faces. Of regions in the extended system for face perception, the amygdala plays a central role in processing the social relevance of information gleaned from faces, particularly when that information may signal a potential threat.

Magnetoencephalographic evidence of early processing of direction of gaze in humans

Despite the crucial importance of direction of gaze in social interactions, it is only recently that there has been interest in human brain responses to gaze direction. Using full-head magnetoencephalography, we investigated the correlates of direction of gaze in full faces and in eyes-only stimuli, measuring the early face-responsive component between 145 and 225 ms. Faces with eyes forward or averted had larger responses than faces with eyes up or closed. For eyes-only stimuli the shortest latencies were seen for eyes averted and the smallest amplitudes were seen for eyes closed. The data were explained by two dipoles in inferior-temporal regions, which showed greater activation for upright faces than face parts or inverted faces, as well as some sensitivity to direction of gaze in this very early stage of processing.

Seen Gaze-Direction Modulates Fusiform Activity and Its Coupling with Other Brain Areas during Face Processing

Gaze-contact is often a preliminary to social interaction and so constitutes a signal for the allocation of processing resources to the gazing face. We investigated how gaze direction influences face processing in an fMRI study, where seen gaze and head direction could independently be direct or deviated. Direct relative to averted gaze elicited stronger activation for faces in ventral occipitotemporal cortices around the fusiform gyrus, regardless of head orientation. Moreover, direct gaze led to greater correlation between activity in the fusiform and the amygdala, a region associated with emotional responses and stimulus saliency. By contrast, faces with averted gaze (again, regardless of head orientation) yielded increased correlation between activity in the fusiform and the intraparietal sulcus, a region associated with shifting attention to the periphery.

Activation reduction in anterior temporal cortices during repeated recognition of faces of personal acquaintances

Repeated recognition of the face of a familiar individual is known to show semantic repetition priming effect. In this study, normal subjects were repeatedly presented faces of their colleagues, and the effect of repetition on the regional cerebral blood flow change was measured using positron emission tomography. They repeated a set of three tasks: the familiar-face detection (F) task, the facial direction discrimination (D) task, and the perceptual control (C) task. During five repetitions of the F task, familiar faces were presented six times from different views in a pseudorandom order. Activation reduction through the repetition of the F tasks was observed in the bilateral anterior (anterolateral to the polar region) temporal cortices which are suggested to be involved in the access to the long-term memory concerning people. The bilateral amygdala, the hypothalamus, and the medial frontal cortices, were constantly activated during the F tasks, and considered to be associated with the behavioral significance of the presented familiar faces. Constant activation was also observed in the bilateral occipitotemporal regions and fusiform gyri and the right medial temporal regions during perception of the faces, and in the left medial temporal regions during the facial familiarity detection task, which are consistent with the results of previous functional brain imaging studies. The results have provided further information about the functional segregation of the anterior temporal regions in face recognition and long-term memory.

Neuropsychology of fear and loathing

For over 60 years, ideas about emotion in neuroscience and psychology have been dominated by a debate on whether emotion can be encompassed within a single, unifying model. In neuroscience, this approach is epitomized by the limbic system theory and, in psychology, by dimensional models of emotion. Comparative research has gradually eroded the limbic model, and some scientists have proposed that certain individual emotions are represented separately in the brain. Evidence from humans consistent with this approach has recently been obtained by studies indicating that signals of fear and disgust are processed by distinct neural substrates. We review this research and its implications for theories of emotion.

The neurobiology of social cognition

Recent studies have begun to elucidate the roles played in social cognition by specific neural structures, genes, and neurotransmitter systems. Cortical regions in the temporal lobe participate in perceiving socially relevant stimuli, whereas the amygdala, right somatosensory cortices, orbitofrontal cortices, and cingulate cortices all participate in linking perception of such stimuli to motivation, emotion, and cognition. Open questions remain about the domain-specificity of social cognition, about its overlap with emotion and with communication, and about the methods best suited for its investigation.

The amygdala: vigilance and emotion

Here we provide a review of the animal and human literature concerning the role of the amygdala in fear conditioning, considering its potential influence over autonomic and hormonal changes, motor behavior and attentional processes. A stimulus that predicts an aversive outcome will change neural transmission in the amygdala to produce the somatic, autonomic and endocrine signs of fear, as well as increased attention to that stimulus. It is now clear that the amygdala is also involved in learning about positively valenced stimuli as well as spatial and motor learning and this review strives to integrate this additional information. A review of available studies examining the human amygdala covers both lesion and electrical stimulation studies as well as the most recent functional neuroimaging studies. Where appropriate, we attempt to integrate basic information on normal amygdala function with our current understanding of psychiatric disorders, including pathological anxiety.

The eyes have it: the neuroethology, function and evolution of social gaze

Gaze is an important component of social interaction. The function, evolution and neurobiology of gaze processing are therefore of interest to a number of researchers. This review discusses the evolutionary role of social gaze in vertebrates (focusing on primates), and a hypothesis that this role has changed substantially for primates compared to other animals. This change may have been driven by morphological changes to the face and eyes of primates, limitations in the facial anatomy of other vertebrates, changes in the ecology of the environment in which primates live, and a necessity to communicate information about the environment, emotional and mental states. The eyes represent different levels of signal value depending on the status, disposition and emotional state of the sender and receiver of such signals. There are regions in the monkey and human brain which contain neurons that respond selectively to faces, bodies and eye gaze. The ability to follow another individual's gaze direction is affected in individuals with autism and other psychopathological disorders, and after particular localized brain lesions. The hypothesis that gaze following is "hard-wired" in the brain, and may be localized within a circuit linking the superior temporal sulcus, amygdala and orbitofrontal cortex is discussed.

Social perception from visual cues: role of the STS region

Social perception refers to initial stages in the processing of information that culminates in the accurate analysis of the dispositions and intentions of other individuals. Single-cell recordings in monkeys, and neurophysiological and neuroimaging studies in humans, reveal that cerebral cortex in and near the superior temporal sulcus (STS) region is an important component of this perceptual system. In monkeys and humans, the STS region is activated by movements of the eyes, mouth, hands and body, suggesting that it is involved in analysis of biological motion. However, it is also activated by static images of the face and body, suggesting that it is sensitive to implied motion and more generally to stimuli that signal the actions of another individual. Subsequent analysis of socially relevant stimuli is carried out in the amygdala and orbitofrontal cortex, which supports a three-structure model proposed by Brothers. The homology of human and monkey areas involved in social perception, and the functional interrelationships between the STS region and the ventral face area, are unresolved issues.

The amygdala theory of autism

Brothers (Brothers L. Concepts in Neuroscience 1990;1:27-51) proposed a network of neural regions that comprise the "social brain", which includes the amygdala. Since the childhood psychiatric condition of autism involves deficits in "social intelligence", it is plausible that autism may be caused by an amygdala abnormality. In this paper we review the evidence for a social function of the amygdala. This includes reference to the Kluver-Bucy syndrome (which Hetzler and Griffin suggested may serve as an animal model of autism). We then review evidence for an amygdala deficit in people with autism, who are well known to have deficits in social behaviour. This includes a detailed summary of our recent functional magnetic resonance imaging (fMRI) study involving judging from the expressions of another person's eyes what that other person might be thinking or feeling. In this study, patients with autism or AS did not activate the amygdala when making mentalistic inferences from the eyes, whilst people without autism did show amygdala activity. The amygdala is therefore proposed to be one of several neural regions that are abnormal in autism. We conclude that the amygdala theory of autism contains promise and suggest some new lines of research.

Passive and active recognition of one's own face

Facial identity recognition has been studied mainly with explicit discrimination requirement and faces of social figures in previous human brain imaging studies. We performed a PET activation study with normal volunteers in facial identity recognition tasks using the subject's own face as visual stimulus. Three tasks were designed so that the activation of the visual representation of the face and the effect of sustained attention to the representation could be separately examined: a control-face recognition task (C), a passive own-face recognition task (no explicit discrimination was required) (P), and an active own-face recognition task (explicit discrimination was required) (A). Increased skin conductance responses during recognition of own face were seen in both task P and task A, suggesting the occurrence of psychophysiological changes during recognition of one's own face. The left fusiform gyrus, the right supramarginal gyrus, the left putamen, and the right hypothalamus were activated in tasks P and A compared with task C. The left fusiform gyrus and the right supramarginal gyrus are considered to be involved in the representation of one's own face. The activation in the right supramarginal gyrus may be associated with the representation of one's own face as a part of one's own body. The prefrontal cortices, the right anterior cingulate, the right presupplementary motor area, and the left insula were specifically activated during task A compared with tasks C and P, indicating that these regions may be involved in the sustained attention to the representation of one's own face.

Distinct representations of eye gaze and identity in the distributed human neural system for face perception

Face perception requires representation of invariant aspects that underlie identity recognition as well as representation of changeable aspects, such as eye gaze and expression, that facilitate social communication. Using functional magnetic resonance imaging (fMRI), we investigated the perception of face identity and eye gaze in the human brain. Perception of face identity was mediated more by regions in the inferior occipital and fusiform gyri, and perception of eye gaze was mediated more by regions in the superior temporal sulci. Eye-gaze perception also seemed to recruit the spatial cognition system in the intraparietal sulcus to encode the direction of another's gaze and to focus attention in that direction.

Social cognition and the human brain

Humans are exceedingly social animals, but the neural underpinnings of social cognition and behavior are not well understood. Studies in humans and other primates have pointed to several structures that play a key role in guiding social behaviors: the amygdala, ventromedial frontal cortices, and right somatosensory-related cortex, among others. These structures appear to mediate between perceptual representations of socially relevant stimuli, such as the sight of conspecifics, and retrieval of knowledge (or elicitation of behaviors) that such stimuli can trigger. Current debates concern the extent to which social cognition draws upon processing specialized for social information, and the relative contributions made to social cognition by innate and acquired knowledge.