Face processing occurs outside the fusiform 'face area' in autism: evidence from functional MRI

Functional neuroimaging of social cognition in pervasive developmental disorders: a brief review

An emerging literature on the neuroanatomical correlates of social cognition in pervasive developmental disorders is reviewed. Studies conducted with high-functioning adults with autism or Asperger's syndrome highlight patterns of decreased activation in ventromedial prefrontal cortex, temporo-parietal junction, amygdala, and periamygdaloid cortex, along with aberrantly increased activation in primary sensory cortices. Future studies should extend these important initial results to younger and more severely affected subjects.

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.

White matter structure in autism: preliminary evidence from diffusion tensor imaging

BACKGROUND

Individuals with autism have severe difficulties in social communication and relationships. Prior studies have suggested that abnormal connections between brain regions important for social cognition may contribute to the social deficits seen in autism.

METHODS

In this study, we used diffusion tensor imaging to investigate white matter structure in seven male children and adolescents with autism and nine age-, gender-, and IQ-matched control subjects.

RESULTS

Reduced fractional anisotropy (FA) values were observed in white matter adjacent to the ventromedial prefrontal cortices and in the anterior cingulate gyri as well as in the temporoparietal junctions. Additional clusters of reduced FA values were seen adjacent to the superior temporal sulcus bilaterally, in the temporal lobes approaching the amygdala bilaterally, in occipitotemporal tracts, and in the corpus callosum.

CONCLUSIONS

Disruption of white matter tracts between regions implicated in social functioning may contribute to impaired social cognition in autism.

Autism clinical trials: biological and medical issues in patient selection and treatment response

Biomedical measures are critical in the initial patient-screening and -selection phases of a clinical trial in autism and related disorders. These measures can also play an important role in the assessment and characterization of response and can provide an opportunity to study underlying etiologic and pathophysiologic processes. Thus, biomedical measures, including clinical laboratory analyses, metabolic screening, and chromosomal analysis, are used to screen for potential safety-related problems, to decrease biological and genetic heterogeneity, and to define subgroups. Neurobiological measures can be examined as possible predictors, modifiers or surrogates of therapeutic response, and adverse effects. Neurobiological research measures can also be used to study mechanisms and extent of drug action and to perform baseline and longitudinal investigations of possible pathophysiologic alterations. The potential utility and desirability of specific measures are considered and the general approach to choosing measures for incorporation is discussed.

Autism and pervasive developmental disorders

The quantity and quality of research into autism and related conditions have increased dramatically in recent years. Consequently we selectively review key accomplishments and highlight directions for future research. More consistent approaches to diagnosis and more rigorous assessment methods have significantly advanced research, although the boundaries of the 'broader phenotype' remain to be defined and the validity of Asperger's disorder as a discrete syndrome remains controversial. Recent epidemiological studies have shown that Autism Spectrum Disorders are common, but there continues to be debate about the causes of the increase in the frequency with which autism is diagnosed. Psychological research has helped to develop new developmental models for the disorder and there have also been significant advances in the molecular genetics of autism and understanding of the underlying neurobiological processes. Areas important for future research include the study of autism as it first develops, i.e., in infants and very young children, and of specific processes (psychological and neurobiological) which underlie the disorder. Significant challenges lie ahead in evaluating the growing number of treatments for autism and in integrating the results of research into treatment and educational settings.

Proton magnetic resonance spectroscopic imaging of the brain in childhood autism

BACKGROUND

Autism is a developmental disorder of unknown neurologic basis. Based on prior work, we used proton magnetic resonance spectroscopic imaging ((1)H- MRSI) to investigate brain structures, including cingulate and caudate, that we hypothesized would reveal metabolic abnormalities in subjects with autism.

METHODS

In 22 children with autism, 5 to 16 years old, and 20 age-matched healthy control subjects, (1)H-MRSI assessed levels of N-acetyl compounds (NAA), choline compounds (Cho), and creatine plus phosphocreatine (Cr) at 272 msec echo-time and 1.5 T.

RESULTS

In subjects with autism compared with control subjects, Cho was 27.2% lower in left inferior anterior cingulate and 19.1% higher in the head of the right caudate nucleus; Cr was 21.1% higher in the head of the right caudate nucleus, but lower in the body of the left caudate nucleus (17.9%) and right occipital cortex (16.6%).

CONCLUSIONS

Results are consistent with altered membrane metabolism, altered energetic metabolism, or both in the left anterior cingulate gyrus, both caudate nuclei, and right occipital cortex in subjects with autism compared with control subjects.

The amygdala and autism: implications from non-human primate studies

Brothers (1990) has proposed that the amygdala is an important component of the neural network that underlies social behavior. Kemper and Bauman (1993) identified neuropathology in the amygdala of the postmortem autistic brain. These findings, along with recent functional neuroimaging data, have led Baron-Cohen et al. (2000) to propose that dysfunction of the amygdala may be responsible, in part, for the impairment of social behavior that is a hallmark feature of autism. Recent data from studies in our laboratory on the effects of amygdala lesions in the adult and infant macaque monkey do not support a fundamental role for the amygdala in social behavior. If the amygdala is not essential for the component processes of social behavior, as seems to be case in both non-human primates and selected patients with bilateral amygdala damage, then it is unlikely to be the primary substrate for the impaired social behavior of autism. However, damage to the amygdala does have an effect on a monkey's response to normally fear-inducing stimuli, such as snakes, and removes a natural reluctance to engage novel conspecifics in social interactions. These findings lead to the conclusion that an important role for the amygdala is in the detection of threats and mobilizing an appropriate behavioral response, part of which is fear. Interestingly, an important comorbid feature of autism is anxiety (Muris et al. 1998). If the amygdala is pathological in subjects with autism, it may contribute to their abnormal fears and increased anxiety rather than their abnormal social behavior.

Dosage-sensitive X-linked locus influences the development of amygdala and orbitofrontal cortex, and fear recognition in humans

The amygdala, which plays a critical role in emotional learning and social cognition, is structurally and functionally sexually dimorphic in humans. We used magnetic neuroimaging and molecular genetic analyses with healthy subjects and patients possessing X-chromosome anomalies to find dosage-sensitive genes that might influence amygdala development. If such X-linked genes lacked a homologue on the Y-chromosome they would be expressed in one copy in normal 46,XY males and two copies in normal 46,XX females. We showed by means of magnetic neuroimaging that 46,XY males possess significantly increased amygdala volumes relative to normal 46,XX females. However, females with Turner syndrome (45,X) have even larger amygdalae than 46,XY males. This finding implies that haploinsufficiency for one or more X-linked genes influences amygdala development irrespective of a direct or indirect (endocrinological) mechanism involving the Y-chromosome. 45,X females also have increased grey matter volume in the orbitofrontal cortex bilaterally, close to a region implicated in emotional learning. They are as poor as patients with bilateral amygdalectomies in the recognition of fear from facial expressions. We attempted to localize the gene(s) responsible for these deficits in X-monosomy by means of a deletion mapping strategy. We studied female patients possessing structural X-anomalies of the short arm. A genetic locus (no greater than 4.96 Mb in size) at Xp11.3 appears to play a key role in amygdala and orbitofrontal structural and (by implication) functional development. Females with partial X-chromosome deletions, in whom this critical locus is deleted, have normal intelligence. Their fear recognition is as poor as that of 45,X females and their amygdalae are correspondingly enlarged. This 4.96 Mb region contains, among others, the genes for monoamine oxidase A (MAOA) and B (MAOB), which are involved in the oxidative deamination of several neurotransmitters, including dopamine and serotonin. Abnormal activity of these neurotransmitters has been implicated in the aetiology of several neurodevelopmental disorders in which social cognitive deficits are prominent. These associated deficits include a specific lack of fear recognition from facial expressions. We show that the thrombocytic activity of MAOB is proportionate to the number of X-chromosomes, and hypothesize that haploinsufficiency of this enzyme in 45,X females predisposes to their deficits in social cognition.

Molecular dissection of the amygdala and its relevance to autism

The limbic system, and in particular the amygdala, have been implicated in autism. The amygdala is a complex structure that in rodents consists of at least 12 different nuclei or subnuclei. A comparative analysis of amygdala neuroanatomy in normal vs. autistic brains would be aided by the availability of molecular markers to unambiguously recognize these different amygdala substructures. Here we report on the development of methods to identify genes enriched in the central, lateral and medial nuclei of the rodent amygdala. Our results suggest that laser-capture microdissection of specific amygdala subnuclei, when combined with linear amplification of cRNA probes for oligonucleotide microarray hybridization, can efficiently identify genes whose expression is confined to these substructures. Importantly, many of these genes were missed in previous gene expression-profiling experiments using whole amygdala tissue. The isolation of human orthologs of these subnucleus-specific genes, and/or the application of these methods directly to human tissue, may provide useful markers for characterizing neuropathological correlates of autism, as well as for identifying molecular differences between normal and autistic brains.

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.

Genetic and neurodevelopmental influences in autistic disorder

OBJECTIVE

In the past, autism was considered to be largely psychogenic. However, research in the last 2 decades indicates that autism is largely caused by genetic factors that lead to abnormal brain development. This article reviews research into the genetic and neurodevelopmental factors underlying autism.

METHODS

We review the findings from genetic and brain-imaging studies of autism over the past 15 years and synthesize these findings as a guide for future research.

RESULTS

Genome scans and association studies have suggested potential genomic regions and genes, respectively, that may be involved in the etiology of autism, and there have been some replications of these results. Similarly, the findings that brain volume is exaggerated in autism and corpus callosum size is reduced have also been independently replicated. Unfortunately, studies of other subcortical structures remain inconclusive or contradictory.

CONCLUSIONS

Overwhelming evidence now supports a neurobiological basis for autism. However, further refinements will be needed to guide future studies, particularly to identify the most informative phenotypes to investigate. Additionally, studies examining the role of genetic factors in the brain abnormalities underlying autism will likely lead to further findings that will enhance our understanding of autism's causes.

Amygdalar activation associated with happy facial expressions in adolescents: a 3-T functional MRI study

OBJECTIVE

To study the possible role of the amygdala in the recognition of happy and sad facial expressions in adolescents aged 13 to 17 years.

METHOD

Twelve healthy adolescents (6 females and 6 males) underwent noninvasive 3-Tesla functional magnetic resonance imaging while viewing pictures of happy, sad, and neutral facial expressions.

RESULTS

Happy faces produced significant bilateral amygdalar activation when compared with neutral faces (p <.05, corrected). Sad faces relative to neutral did not produce significant amygdalar activation.

CONCLUSIONS

These results extend the role of the amygdala in adolescents to include the recognition of happy facial expressions. They demonstrate the feasibility of using happy facial expressions to noninvasively study amygdalar function in adolescents and establish a baseline against which the amygdalar response to emotional stimuli in several psychiatric conditions may be compared.

Eye contact does not facilitate detection in children with autism

Eye contact is crucial in achieving social communication. Deviant patterns of eye contact behavior are found in individuals with autism, who suffer from severe social and communicative deficits. This study used a visual oddball paradigm to investigate whether children with high functioning autism have difficulty in detecting mutual gaze under experimental conditions. The results revealed that children with autism were no better at detecting direct gaze than at detecting averted gaze, which is unlike normal children. This suggests that whereas typically developing children have the ability to detect direct gaze, children with autism do not. This might result in altered eye-contact behavior, which hampers subsequent development of social and communicative skills.

A secretin i.v. infusion activates gene expression in the central amygdala of rats

For the last 100 years secretin has been extensively studied for its hormonal effects on digestion. Recent observations that the deficits in social reciprocity skills seen in young (3-4-year-old) autistic children are improved after secretin infusions suggest an additional influence on neuronal activity. We show here that i.v. administration of secretin in rats induces Fos protein expression in the neurons of the central amygdala as well as the area postrema, bed nucleus of the stria terminalis, external lateral parabrachial nucleus and supraoptic nucleus. However, secretin infusion did not induce Fos expression in the solitary tract nucleus or paraventricular nucleus, regions normally activated by related peptides such as cholecystokinin. The peak blood levels of secretin that induce Fos protein expression in rat brain are similar to the peak blood levels observed during i.v. treatment with secretin in humans. The amygdala is known to be critical for developing reciprocal social interaction skills and abnormalities in this brain region have been demonstrated in autistic children.

Automatic attention cueing through eye movement in 2-year-old children with autism

Automatic attention cueing by perceived changes in gaze direction was studied in 2-year-old children with autism and typically developing (TD) controls using a visual attention cueing paradigm. In Experiments 1 and 2 the cue consisted of an eye movement (Eyes) and a nonbiological movement (SimEyes), respectively. The results suggest that visual attention in children with autism and their TD counterparts is cued by perceived eye movement. Thus, although in naturalistic situations toddlers with autism do not follow the gaze of others, they are sensitive to directional cues inherent in eye movement. Cue-specific differences in performance related to the level of engagement and cue-processing time may suggest reliance on different underlying strategies for gaze processing in autism.

Holistic and part-based face recognition in children with autism

BACKGROUND

There is substantial evidence that children with autism are impaired in face recognition. Although many researchers have suggested that this impairment derives from a failure of holistic face processing and a tendency to represent and encode faces on a part-by-part basis, this hypothesis has not been tested directly.

METHOD

Holistic face processing was assessed by comparing children's ability to recognize a face part (eyes, nose, or mouth) in the context of the whole face in which it was learned with their ability to recognize the same face part in isolation.

RESULTS

In Study 1, as expected, typically developing 9-year-olds (n = 27) and 11-year-olds (n = 30) were significantly better at recognizing face parts presented in the whole than in the part test condition, and this effect was limited to upright faces and not found for inverted faces. Consistent with prior findings, typically developing children were most accurate when face recognition depended on the eyes. In Study 2, high-functioning children with autism (n = 22) evidenced a whole-test advantage for mouths only, and were markedly deficient when face recognition depended on the eyes. Their pattern of performance diverged from age- and IQ-matched comparison participants (n = 20), who performed similarly to the typically developing children in Study 1.

CONCLUSIONS

These findings suggest that face recognition abnormalities in autism are not fully explained by an impairment of holistic face processing, and that there is an unusual significance accorded to the mouth region when children with autism process information from people's faces.

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.

Disorders of face perception and recognition

Face recognition is one of the most complex visual tasks performed by the human brain. Data from monkeys suggest that area IT may play a key role in identifying faces, and functional imaging research suggests that the human homologue of IT may be located in the medial occipitotemporal cortex, where a FFA has been located. Damage to medial occipitotemporal structures on the right or bilaterally leads to prosopagnosia, the failure to recognize facial identity. Prosopagnosia is not a single functional disorder but a family of dysfunctions, with different patients having different degrees of impairments to various perceptual and memory stages involved in face processing. Understanding the perceptual basis of this disorder and epiphenomena, such as covert recognition, is a goal of current research. Deficits in face perception also may contribute to Capgras syndrome and may be related to the impaired social development of patients with Asperger syndrome. More recently, identified deficits in face processing include the false recognition of unfamiliar faces and the impaired extraction of social information from faces, independent of the recognition of identity. Many of these prosopagnosia and other face processing deficits can be placed in the context of cognitive models of face processing stages, which are being refined continually by data from neurologic patients and functional imaging in normal subjects.

Dissociations of cerebral cortex, subcortical and cerebral white matter volumes in autistic boys

High-functioning autistic and normal school-age boys were compared using a whole-brain morphometric profile that includes both total brain volume and volumes of all major brain regions. We performed MRI-based morphometric analysis on the brains of 17 autistic and 15 control subjects, all male with normal intelligence, aged 7-11 years. Clinical neuroradiologists judged the brains of all subjects to be clinically normal. The entire brain was segmented into cerebrum, cerebellum, brainstem and ventricles. The cerebrum was subdivided into cerebral cortex, cerebral white matter, hippocampus-amygdala, caudate nucleus, globus pallidus plus putamen, and diencephalon (thalamus plus ventral diencephalon). Volumes were derived for each region and compared between groups both before and after adjustment for variation in total brain volume. Factor analysis was then used to group brain regions based on their intercorrelations. Volumes were significantly different between groups overall; and diencephalon, cerebral white matter, cerebellum and globus pallidus-putamen were significantly larger in the autistic group. Brain volumes were not significantly different overall after adjustment for total brain size, but this analysis approached significance and effect sizes and univariate comparisons remained notable for three regions, although not all in the same direction: cerebral white matter showed a trend towards being disproportionately larger in autistic boys, while cerebral cortex and hippocampus-amygdala showed trends toward being disproportionately smaller. Factor analysis of all brain region volumes yielded three factors, with central white matter grouping alone, and with cerebral cortex and hippocampus-amygdala grouping separately from other grey matter regions. This morphometric profile of the autistic brain suggests that there is an overall increase in brain volumes compared with controls. Additionally, results suggest that there may be differential effects driving white matter to be larger and cerebral cortex and hippocampus-amygdala to be relatively smaller in the autistic than in the typically developing brain. The cause of this apparent dissociation of cerebral cortical regions from subcortical regions and of cortical white from grey matter is unknown, and merits further investigation.

The neurobiology of autism: new pieces of the puzzle

The neurobiologic basis of autism is reviewed, with discussion of evidence from genetic, magnetic resonance imaging, neuropathology, and functional neuroimaging studies. Although autism is a behaviorally valid syndrome, it is remarkably heterogeneous and involves multiple developmental domains as well as a wide range of cognitive, language, and socioemotional functioning. Although multiple etiologies are implicated, recent advances have identified common themes in pathophysiology. Genetic factors play a primary role, based on evidence from family studies, identification of putative genes using genome-wide linkage analyses, and comorbidities with known genetic mutations. The RELN gene, which codes for an extracellular protein guiding neuronal migration, has been implicated in autism. Numerous neuropathologic changes have been described, including macroencephaly, acceleration and then deceleration in brain growth, increased neuronal packing and decreased cell size in the limbic system, and decreased Purkinje cell number in the cerebellum. Abnormalities in organization of the cortical minicolumn, representing the fundamental subunit of vertical cortical organization, may underlie the pathology of autism and result in altered thalamocortical connections, cortical disinhibition, and dysfunction of the arousal-modulating system of the brain. The role of acquired factors is speculative, with insufficient evidence to link the measles-mumps-rubella (MMR) vaccine with autism or to change immunization practices.

Organization of language networks in children: functional magnetic resonance imaging studies

Functional magnetic resonance imaging (fMRI) is a relatively new neuroimaging procedure that has been used to study a wide variety of cognitive phenomena in adults, including attention, language, and memory. More recently, this technique has been successfully applied to pediatric populations as well. In particular, many investigators have employed fMRI as a tool to study language development in normal children. This paper reviews the current imaging research on the identification of cortex subserving components of language processing in young children. The literature suggests that fMRI can successfully identify regions of language cortex in children in much the same capacity as it can with adults, and that generally, adults and children show fundamental similarities in the patterns of activation. However, special considerations with pediatric imaging, paradigm design, and image analysis are also discussed.

Understanding autism: insights from mind and brain

Autism is a developmental disorder characterized by impaired social interaction and communication as well as repetitive behaviours and restricted interests. The consequences of this disorder for everyday life adaptation are extremely variable. The general public is now more aware of the high prevalence of this lifelong disorder, with ca. 0.6% of the population being affected. However, the signs and symptoms of autism are still puzzling. Since a biological basis of autism was accepted, approaches from developmental cognitive neuroscience have been applied to further our understanding of the autism spectrum. The study of the behavioural and underlying cognitive deficits in autism has advanced ahead of the study of the underlying brain abnormalities and of the putative genetic mechanisms. However, advances in these fields are expected as methodological difficulties are overcome. In this paper, recent developments in the field of autism are outlined. In particular, we review the findings of the three main neuro-cognitive theories of autism: theory-of-mind deficit, weak central coherence and executive dysfunction.

The role of the fusiform face area in social cognition: implications for the pathobiology of autism

A region in the lateral aspect of the fusiform gyrus (FG) is more engaged by human faces than any other category of image. It has come to be known as the 'fusiform face area' (FFA). The origin and extent of this specialization is currently a topic of great interest and debate. This is of special relevance to autism, because recent studies have shown that the FFA is hypoactive to faces in this disorder. In two linked functional magnetic resonance imaging (fMRI) studies of healthy young adults, we show here that the FFA is engaged by a social attribution task (SAT) involving perception of human-like interactions among three simple geometric shapes. The amygdala, temporal pole, medial prefrontal cortex, inferolateral frontal cortex and superior temporal sulci were also significantly engaged. Activation of the FFA to a task without faces challenges the received view that the FFA is restricted in its activities to the perception of faces. We speculate that abstract semantic information associated with faces is encoded in the FG region and retrieved for social computations. From this perspective, the literature on hypoactivation of the FFA in autism may be interpreted as a reflection of a core social cognitive mechanism underlying the disorder.

Investigating individual differences in brain abnormalities in autism

Autism is a psychiatric syndrome characterized by impairments in three domains: social interaction, communication, and restricted and repetitive behaviours and interests. Recent findings implicate the amygdala in the neurobiology of autism. In this paper, we report the results of a series of novel experimental investigations focusing on the structure and function of the amygdala in a group of children with autism. The first section attempts to determine if abnormality of the amygdala can be identified in an individual using magnetic resonance imaging in vivo. Using single-case voxel-based morphometric analyses, abnormality in the amygdala was detected in half the children with autism. Abnormalities in other regions were also found. In the second section, emotional modulation of the startle response was investigated in the group of autistic children. Surprisingly, there were no significant differences between the patterns of emotional modulation of the startle response in the autistic group compared with the controls.

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.

The human amygdala and the emotional evaluation of sensory stimuli

A wealth of animal data implicates the amygdala in aspects of emotional processing. In recent years, functional neuroimaging and neuropsychological studies have begun to refine our understanding of the functions of the amygdala in humans. This literature offers insights into the types of stimuli that engage the amygdala and the functional consequences that result from this engagement. Specific conclusions and hypotheses include: (1) the amygdala activates during exposure to aversive stimuli from multiple sensory modalities; (2) the amygdala responds to positively valenced stimuli, but these responses are less consistent than those induced by aversive stimuli; (3) amygdala responses are modulated by the arousal level, hedonic strength or current motivational value of stimuli; (4) amygdala responses are subject to rapid habituation; (5) the temporal characteristics of amygdala responses vary across stimulus categories and subject populations; (6) emotionally valenced stimuli need not reach conscious awareness to engage amygdala processing; (7) conscious hedonic appraisals do not require amygdala activation; (8) activation of the amygdala is associated with modulation of motor readiness, autonomic functions, and cognitive processes including attention and memory; (9) amygdala activations do not conform to traditional models of the lateralization of emotion; and (10) the extent and laterality of amygdala activations are related to factors including psychiatric status, gender and personality. The strengths and weakness of these hypotheses and conclusions are discussed with reference to the animal literature.

Abnormal asymmetry in language association cortex in autism

Autism is a neurodevelopmental disorder affecting cognitive, language, and social functioning. Although language and social communication abnormalities are characteristic, prior structural imaging studies have not examined language-related cortex in autistic and control subjects. Subjects included 16 boys with autism (aged 7-11 years), with nonverbal IQ greater than 80, and 15 age- and handedness-matched controls. Magnetic resonance brain images were segmented into gray and white matter; cerebral cortex was parcellated into 48 gyral-based divisions per hemisphere. Asymmetry was assessed a priori in language-related inferior lateral frontal and posterior superior temporal regions and assessed post hoc in all regions to determine specificity of asymmetry abnormalities. Boys with autism had significant asymmetry reversal in frontal language-related cortex: 27% larger on the right in autism and 17% larger on the left in controls. Only one additional region had significant asymmetry differences on post hoc analysis: posterior temporal fusiform gyrus (more left-sided in autism), whereas adjacent fusiform gyrus and temporooccipital inferior temporal gyrus both approached significance (more right-sided in autism). These inferior temporal regions are involved in visual face processing. In boys with autism, language and social/face processing-related regions displayed abnormal asymmetry. These structural abnormalities may relate to language and social disturbances observed in autism.

Brain structural abnormalities in young children with autism spectrum disorder

OBJECTIVE

To explore the specific gross neuroanatomic substrates of this brain developmental disorder, the authors examine brain morphometric features in a large sample of carefully diagnosed 3- to 4-year-old children with autism spectrum disorder (ASD) compared with age-matched control groups of typically developing (TD) children and developmentally delayed (DD) children.

METHODS

Volumes of the cerebrum, cerebellum, amygdala, and hippocampus were measured from three-dimensional coronal MR images acquired from 45 children with ASD, 26 TD children, and 14 DD children. The volumes were analyzed with respect to age, sex, volume of the cerebrum, and clinical status.

RESULTS

Children with ASD were found to have significantly increased cerebral volumes compared with TD and DD children. Cerebellar volume for the ASD group was increased in comparison with the TD group, but this increase was proportional to overall increases in cerebral volume. The DD group had smaller cerebellar volumes compared with both of the other groups. Measurements of amygdalae and hippocampi in this group of young children with ASD revealed enlargement bilaterally that was proportional to overall increases in total cerebral volume. There were similar findings of cerebral enlargement for both girls and boys with ASD. For subregion analyses, structural abnormalities were observed primarily in boys, although this may reflect low statistical power issues because of the small sample (seven girls with ASD) studied. Among the ASD group, structural findings were independent of nonverbal IQ. In a subgroup of children with ASD with strictly defined autism, amygdalar enlargement was in excess of increased cerebral volume.

CONCLUSIONS

These structural findings suggest abnormal brain developmental processes early in the clinical course of autism. Research currently is underway to better elucidate mechanisms underlying these structural abnormalities and their longitudinal progression.

Structural and functional magnetic resonance imaging of autism

Magnetic resonance imaging (MRI) of brain structures and function is uniquely suited to characterize the range of neuroanatomical and physiological changes that characterize the autism phenotype as it develops over time. In this review, we examine the scientific literature in MRI as applied to autism and related areas, over approximately the last decade, discussing findings which have emerged, methodological stumbling blocks which have been identified, and potential future directions. Structural MRI studies have recently begun to elucidate the neurodevelopmental underpinnings and brain-behavior relationships in autism while fMRI studies, building on the wealth of data in normal individuals, are beginning to characterize the underlying neuropsychological deficits of the disorder. Together, these two methods combine to contribute to a better understanding of the neural basis and brain phenotype of this disorder.

Studies of altered social cognition in neuropsychiatric disorders using functional neuroimaging

In this paper, we review studies using functional neuroimaging to examine cognition in neuropsychiatric disorders. The focus is on social cognition, which is a topic that has received increasing attention over the past few years. A network of brain regions is proposed for social cognition that includes regions involved in processes relevant to social functioning (for example, self reference and emotion). We discuss the alterations of activity in these areas in patients with autism, depression, schizophrenia, and posttraumatic stress disorders in relation to deficits in social behaviour and symptoms. The evidence to date suggests that there may be some specificity of the brain regions involved in these 4 disorders, but all are associated with dysfunction in the amygdala and dorsal cingulate gyrus. Although there is much work remaining in this area, we are beginning to understand the complex interactions of brain function and behaviour that lead to disruptions of social abilities.

The utility of functional magnetic resonance imaging in epilepsy and language

Functional magnetic resonance imaging (fMRI) is a viable presurgical tool for use with the pediatric epilepsy population as replacement for the intra-carotid sodium amobarbital test (IAT) used to identify hemispheric language dominance. This paper reviews the current imaging research on the identification of language cortex in pediatric epilepsy patients and in normal children. A review of the literature comparing fMRI to the IAT and electrocortical stimulation suggests that fMRI reliably identifies the dominant hemisphere, with pediatric and adult studies producing comparable results. Within-hemisphere localization of eloquent cortex with fMRI is more problematic. Paradigm selection, data analysis techniques, and considerations specific to imaging children are discussed. Utility of fMRI for studying neural plasticity as a result of brain insult (e.g., epilepsy) is also considered.