Repetition Suppression and Memory for Faces is Reduced in Adults with Autism Spectrum Conditions

Autism spectrum conditions (ASC) are associated with a number of atypicalities in face processing, including difficulties in face memory. However, the neural mechanisms underlying this difficulty are unclear. In neurotypical individuals, repeated presentation of the same face is associated with a reduction in activity, known as repetition suppression (RS), in the fusiform face area (FFA). However, to date, no studies have investigated RS to faces in individuals with ASC, or the relationship between RS and face memory. Here, we measured RS to faces and geometric shapes in individuals with a clinical diagnosis of an ASC and in age and IQ matched controls. Relative to controls, the ASC group showed reduced RS to faces in bilateral FFA and reduced performance on a standardized test of face memory. By contrast, RS to shapes in object-selective regions and object memory did not differ between groups. Individual variation in face-memory performance was positively correlated with RS in regions of left parietal and prefrontal cortex. These findings suggest difficulties in face memory in ASC may be a consequence of differences in the way faces are stored and/or maintained across a network of regions involved in both visual perception and short-term/working memory.

High autistic trait individuals do not modulate gaze behaviour in response to social presence but look away more when actively engaged in an interaction

Autism is characterised by difficulties in social functioning, notably in interactions with other people. Yet, most studies addressing social difficulties have used static images or, at best, videos of social stimuli, with no scope for real interaction. Here, we study one crucial aspect of social interactions—gaze behaviour—in an interactive setting. First, typical individuals were shown videos of an experimenter and, by means of a deception procedure, were either led to believe that the experimenter was present via a live video‐feed or was pre‐recorded. Participants' eye movements revealed that when passively viewing an experimenter they believed to be “live,” they looked less at that person than when they believed the experimenter video was pre‐recorded. Interestingly, this reduction in viewing behaviour in response to the believed “live” presence of the experimenter was absent in individuals high in autistic traits, suggesting a relative insensitivity to social presence alone. When participants were asked to actively engage in a real‐time interaction with the experimenter, however, high autistic trait individuals looked significantly less at the experimenter relative to low autistic trait individuals. The results reinforce findings of atypical gaze behaviour in individuals high in autistic traits, but suggest that active engagement in a social interaction may be important in eliciting reduced looking. We propose that difficulties with the spatio‐temporal dynamics associated with real social interactions rather than underlying difficulties processing the social stimulus itself may drive these effects. The results underline the importance of developing ecologically valid methods to investigate social cognition. Autism Res2017, 10: 359–368. © 2016 The Authors Autism Research published by Wiley Periodicals, Inc. on behalf of International Society for Autism Research.

Intact priors for gaze direction in adults with high-functioning autism spectrum conditions

BACKGROUND

Autism Spectrum Conditions (ASC) are associated with a range of perceptual atypicalities, including abnormalities in gaze processing. Pellicano and Burr (Trends Cogn Sci 16(10):504-10, 2012) have argued that these atypicalities might be explained within a Bayesian framework, in which perception represents the combination of sensory information with prior knowledge. They propose that the Bayesian priors of individuals with ASC might be attenuated, such that their perception is less reliant on prior knowledge than neurotypical individuals. An important tenet of Bayesian decision theory is that increased uncertainty about incoming sensory information will lead to a greater influence of the prior on perception. Consistent with this, Mareschal et al. (Curr Biol 23(8):717-21, 2013) showed that when noise is added to the eyes of a face (increasing uncertainty about gaze direction), gaze is more likely to be perceived as direct.

METHODS

We adopted the same paradigm as Mareschal et al. to determine whether the influence of a prior on gaze perception is reduced in neurotypical participants with high numbers of autistic traits (experiment 1) and in individuals with a clinical diagnosis of ASC (experiment 2). Participants were presented with synthetic faces and asked to make a judgement about the relative gaze directions of the faces. Uncertainty about gaze direction was manipulated by adding noise to the eyes of a face.

RESULTS

Consistent with previous work, in both experiment 1 and experiment 2, participants showed a bias towards perceiving gaze as direct under conditions of uncertainty. However, there was no evidence that the magnitude of this bias was reduced either in the ASC group or in neurotypical controls with a high number of autistic traits.

CONCLUSIONS

Our findings challenge the attenuated priors theory of perception in ASC (Trends Cogn Sci 16(10):504-10, 2012) and related proposals (Trends Cogn Sci 17(1):1, 2013, Front Hum Neurosci 8:302, 2014), and suggest priors for gaze direction are intact in high-functioning ASC.

The effect of perceptual expectation on repetition suppression to faces is not modulated by variation in autistic traits

There is substantial variation in the magnitude of the repetition suppression (RS) effects across individuals; however the causes of this variation remain unclear. In a recent study, we found that RS in occipitotemporal cortex was negatively related to individual variation in autistic traits in a neurotypical population. Recent proposals have considered autistic behaviours within a Bayesian framework, suggesting that individuals with autism may have 'attenuated priors' (i.e., their perception is less influenced by prior information). Predictive coding represents a neural instantiation of Bayesian inference, and characterises RS as reduction in prediction error between 'top-down' (prior beliefs) and 'bottom-up' (stimulus related) inputs. In accordance with this, evidence shows that RS is greater when repetition of a stimulus is expected relative to when it is unexpected. Here, using an established paradigm which manipulates the probability of stimulus repetition, we investigated the effect of perceptual expectation on RS in a group of neurotypical individuals varying on a measure of autistic traits. We predicted that the magnitude of the perceptual expectation effect would be negatively related to individual differences in autistic traits. We found a significant effect of perceptual expectation on RS in face-selective regions (i.e., greater RS when repetitions were expected relative to unexpected). However, there was no evidence of a relationship between autistic traits and the magnitude of this effect in any face-selective region of interest (ROI). These findings provide a challenge for the proposal that autism spectrum conditions (ASC) may be associated with the attenuated influence of prior information.

Obesity-associated melanocortin-4 receptor mutations are associated with changes in the brain response to food cues

CONTEXT

Mutations in the melanocortin-4 receptor (MC4R) represent the commonest genetic form of obesity and are associated with hyperphagia.

OBJECTIVE

The aim of this study was to investigate whether melanocortin signaling modulates anticipatory food reward by studying the brain activation response to food cues in individuals with MC4R mutations. Design/Setting/Participants/Main Outcome Measure: We used functional magnetic resonance imaging to measure blood oxygen level-dependent responses to images of highly palatable, appetizing foods, bland foods, and non-food objects in eight obese individuals with MC4R mutations, 10 equally obese controls, and eight lean controls with normal MC4R genotypes. Based on previous evidence, we performed a region-of-interest analysis centered on the caudate/putamen (dorsal striatum) and ventral striatum.

RESULTS

Compared to non-foods, appetizing foods were associated with activation in the dorsal and ventral striatum in lean controls and in MC4R-deficient individuals. Surprisingly, we observed reduced activation of the dorsal and ventral striatum in obese controls relative to MC4R-deficient patients and lean controls. There were no group differences for the contrast of disgusting foods with bland foods or non-foods, suggesting that the effects observed in response to appetizing foods were not related to arousal.

CONCLUSION

We identified differences in the striatal response to food cues between two groups of obese individuals, those with and those without MC4R mutations. These findings are consistent with a role for central melanocortinergic circuits in the neural response to visual food cues.

Repetition Suppression in Ventral Visual Cortex Is Diminished as a Function of Increasing Autistic Traits

Repeated viewing of a stimulus causes a change in perceptual sensitivity, known as a visual aftereffect. Similarly, in neuroimaging, repetitions of the same stimulus result in a reduction in the neural response, known as repetition suppression (RS). Previous research shows that aftereffects for faces are reduced in both children with autism and in first-degree relatives. With functional magnetic resonance imaging, we found that the magnitude of RS to faces in neurotypical participants was negatively correlated with individual differences in autistic traits. We replicated this finding in a second experiment, while additional experiments showed that autistic traits also negatively predicted RS to images of scenes and simple geometric shapes. These findings suggest that a core aspect of neural function--the brain's response to repetition--is modulated by autistic traits.

Direct gaze elicits atypical activation of the theory-of-mind network in autism spectrum conditions

Eye contact plays a key role in social interaction and is frequently reported to be atypical in individuals with autism spectrum conditions (ASCs). Despite the importance of direct gaze, previous functional magnetic resonance imaging in ASC has generally focused on paradigms using averted gaze. The current study sought to determine the neural processing of faces displaying direct and averted gaze in 18 males with ASC and 23 matched controls. Controls showed an increased response to direct gaze in brain areas implicated in theory-of-mind and gaze perception, including medial prefrontal cortex, temporoparietal junction, posterior superior temporal sulcus region, and amygdala. In contrast, the same regions showed an increased response to averted gaze in individuals with an ASC. This difference was confirmed by a significant gaze direction × group interaction. Relative to controls, participants with ASC also showed reduced functional connectivity between these regions. We suggest that, in the typical brain, perceiving another person gazing directly at you triggers spontaneous attributions of mental states (e.g. he is “interested” in me), and that such mental state attributions to direct gaze may be reduced or absent in the autistic brain.

Reduced functional connectivity within and between 'social' resting state networks in autism spectrum conditions

Individuals with Autism Spectrum Conditions (ASC) have difficulties in social interaction and communication, which is reflected in hypoactivation of brain regions engaged in social processing, such as medial prefrontal cortex (mPFC), amygdala and insula. Resting state studies in ASC have identified reduced connectivity of the default mode network (DMN), which includes mPFC, suggesting that other resting state networks incorporating ‘social’ brain regions may also be abnormal. Using Seed-based Connectivity and Group Independent Component Analysis (ICA) approaches, we looked at resting functional connectivity in ASC between specific ‘social’ brain regions, as well as within and between whole networks incorporating these regions. We found reduced functional connectivity within the DMN in individuals with ASC, using both ICA and seed-based approaches. Two further networks identified by ICA, the salience network, incorporating the insula and a medial temporal lobe network, incorporating the amygdala, showed reduced inter-network connectivity. This was underlined by reduced seed-based connectivity between the insula and amygdala. The results demonstrate significantly reduced functional connectivity within and between resting state networks incorporating ‘social’ brain regions. This reduced connectivity may result in difficulties in communication and integration of information across these networks, which could contribute to the impaired processing of social signals in ASC.

Brain structure abnormalities in early-onset and adolescent-onset conduct disorder

OBJECTIVE

The developmental taxonomic theory proposes that neurodevelopmental factors play a critical role in the etiology of early-onset conduct disorder, whereas adolescent-onset conduct disorder arises as a result of social mimicry of deviant peers. Recent studies have challenged this theory by demonstrating that adolescents with both early- and adolescent-onset forms of conduct disorder show impaired emotional learning and abnormal neural activation during facial expression processing. The present study extends this work by investigating brain structure in both subtypes of conduct disorder.

METHOD

Voxel-based morphometry was used to compare gray matter volumes in four regions of interest (amygdala, insula, anterior cingulate, and orbitofrontal cortex) in male adolescents with early-onset (N=36) or adolescent-onset (N=27) conduct disorder and in healthy comparison subjects (N=27). Whole-brain structural analyses were also performed.

RESULTS

The combined conduct disorder group displayed gray matter volume reductions in the bilateral amygdala, extending into the insula, relative to healthy comparison subjects. Separate comparisons between healthy subjects and each conduct disorder subgroup revealed lower amygdala volume in both subgroups and reduced right insula volume in the adolescent-onset subgroup. Regression analyses within the conduct disorder subjects alone demonstrated a negative correlation between conduct disorder symptoms and right insula volume.

CONCLUSIONS

The results demonstrate that gray matter volume reductions in brain regions involved in processing socioemotional stimuli are associated with conduct disorder, regardless of age of onset. Brain structural abnormalities may contribute to the emergence of adolescent-onset as well as early-onset conduct disorder.

The serotonin transporter gene polymorphism and the effect of baseline on amygdala response to emotional faces

Previous research has found that a common polymorphism in the serotonin transporter gene (5-HTTLPR) is an important mediator of individual differences in brain responses associated with emotional behaviour. In particular, relative to individuals homozygous for the l-allele, carriers of the s-allele display heightened amygdala activation to emotional compared to non-emotional stimuli. However, there is some debate as to whether this difference is driven by increased activation to emotional stimuli, resting baseline differences between the groups, or decreased activation to neutral stimuli. We performed functional imaging during an implicit facial expression processing task in which participants viewed angry, sad and neutral faces. In addition to neutral faces, we included two further baseline conditions, houses and fixation. We found increased amygdala activation in s-allele carriers relative to l-homozygotes in response to angry faces compared to neutral faces, houses and fixation. When comparing neutral faces to houses or fixation, we found no significant difference in amygdala response between the two groups. In addition, there was no significant difference between the groups in response to fixation when compared with a houses baseline. Overall, these results suggest that the increased amygdala response observed in s-allele carriers to emotional faces is primarily driven by an increased response to emotional faces rather than a decreased response to neutral faces or an increased resting baseline. The results are discussed in relation to the tonic and phasic hypotheses of 5-HTTLPR-mediated modulation of amygdala activity.

Autism spectrum traits in the typical population predict structure and function in the posterior superior temporal sulcus

Autism spectrum disorders (ASDs) are typically characterized by impaired social interaction and communication, narrow interests, and repetitive behaviors. The heterogeneity in the severity of these characteristics across individuals with ASD has led some researchers to suggest that these disorders form a continuum which extends into the general, or “typical,” population, and there is growing evidence that the extent to which typical adults display autistic traits, as measured using the autism-spectrum quotient (AQ), predicts performance on behavioral tasks that are impaired in ASD. Here, we show that variation in autism spectrum traits is related to cortical structure and function within the typical population. Voxel-based morphometry showed that increased AQ scores were associated with decreased white matter volume in the posterior superior temporal sulcus (pSTS), a region important in processing socially relevant stimuli and associated with structural and functional impairments in ASD. In addition, AQ was correlated with the extent of cortical deactivation of an adjacent area of pSTS during a Stroop task relative to rest, reflecting variation in resting state function. The results provide evidence that autism spectrum characteristics are reflected in neural structure and function across the typical (non-ASD) population.

Leaving a bad taste in your mouth but not in my insula

Previous research has implicated regions of anterior insula/frontal operculum in processing conspecific facial expressions of disgust. It has been suggested however that there are a variety of disgust facial expression components which relate to the disgust-eliciting stimulus. The nose wrinkle is predominantly associated with irritating or offensive smells, the mouth gape and tongue extrusion with distaste and oral irritation, while a broader range of disgust elicitors including aversive interpersonal contacts and certain moral offenses are associated primarily with the upper lip curl. Using functional magnetic resonance imaging, we show that activity in the anterior insula/frontal operculum is seen only in response to canonical disgust faces, exhibiting the nose wrinkle and upper lip curl, and not in response to distaste facial expressions, exhibiting a mouth gape and tongue protrusion. Canonical disgust expressions also result in activity in brain regions linked to social cognition more broadly, including dorsal medial prefrontal cortex, posterior cingulate cortex, temporo-parietal junction and superior temporal sulcus. We interpret these differences in relation to the relative functional and communicative roles of the different disgust expressions and suggest a significant role for appraisal processes in the insula activation to facial expressions of disgust.

Identifying human albinism: a comparison of VEP and fMRI

PURPOSE

To compare VEP and fMRI as a means of detecting the abnormal visual projections in albinism in different stimulation conditions.

METHODS

Cortical response to monocular full-field pattern-onset and hemifield pattern-onset and -reversal stimulation of 18 subjects with a known diagnosis of albinism, 17 control subjects, and 6 control subjects with infantile nystagmus syndrome (INS) was determined by VEP and fMRI. An asymmetry index was used to quantify the extent of response lateralization as measured by both VEP and fMRI. The extent to which each method and stimulus combination differentiated participant groups was summarized with a receiver operating characteristic (ROC) analysis, where A(A-C) and A(A-N) refer to areas under the ROC curve for albino versus control and albino versus nystagmus comparisons.

RESULTS

Cortical response to full-field monocular stimulation conditions offered robust detection of the abnormal response lateralization in albinism, with fMRI (A(A-C) = 1.00; A(A-N) = 0.91) being slightly more robust than the VEP under these conditions (A(A-C) = 0.91; A(A-N) = 0.79). Hemifield stimulation paradigms were somewhat poorer at differentiating between groups, particularly when VEP was used in combination with pattern-reversal stimulation (pattern-onset fMRI A(A-C) = 0.94, A(A-N) = 0.84, and VEP A(A-C) = 0.86, A(A-N) = 0.86; pattern-reversal fMRI A(A-C) = 0.90, A(A-N) = 0.88, and VEP A(A-C) = 0.69, A(A-N) = 0.64). However, when only the most posterior aspects of the occipital lobe were considered with hemifield stimulation, fMRI achieved the best differentiation between the subject groups, most notably with hemifield pattern-reversal stimulation (A(A-C) = 1.00; A(A-N) = 1.00).

CONCLUSIONS

An interocular comparison between the lateralization of cortical responses elicited by full-field stimulation reliably distinguished between those with albinism and control groups, when both fMRI and VEP were used to assess cortical responses. Hemifield stimulation of one eye offers an alternative method for assessing misrouting associated with albinism and is highly effective when cortical signals are assessed with fMRI, but less so when VEP is used.

Pigmentation predicts the shift in the line of decussation in humans with albinism

In albinism a large proportion of nerve fibres originating in temporal retina cross the midline at the chiasm and project to the contralateral hemisphere. Studies in rodents with albinism have suggested that the extent of this misrouting at the chiasm is inversely related to pigmentation levels. Here, we examine whether there is evidence for a similar relationship in humans with albinism. Functional MRI was performed on 18 subjects with albinism, 17 control subjects and six controls with nystagmus as they underwent hemifield visual stimulation of nasal or temporal retina. Functional activation in 16 coronal slices beginning at the posterior occipital lobes were analysed and the extent of hemispheric response lateralization at each slice position was determined. During temporal retina stimulation, the control response was lateralized to the hemisphere ipsilateral to the stimulated eye for all slices. In albinos, the response in posterior slices was predominantly in the contralateral hemisphere, consistent with misrouting of temporal retina fibres. However, as slice location became progressively anterior, response lateralization reverted to the ipsilateral hemisphere. The slice location at which the transition from contra- to ipsilateralization occurred provided an estimate of the extent of fibre misrouting in the individual. The slice transition location correlated negatively with pigmentation level, providing the first evidence for a relationship between pigmentation and the extent of misrouting in humans with albinism.

Retinal abnormalities in human albinism translate into a reduction of grey matter in the occipital cortex

Albinism is a genetic condition associated with abnormalities of the visual system. Defects in melanin production cause underdevelopment of the fovea, reduced retinal cell numbers and abnormal routing of ganglion cell nerve fibres at the optic chiasm. We examined 19 subjects with albinism and 26 control subjects to determine whether retinal abnormalities affect the structure of the visual cortex. Whole-brain, high-resolution anatomical magnetic resonance imaging volumes from each subject were obtained on a 1.5-T scanner and segmented into grey and white matter. A voxel-wise statistical comparison of grey and white matter volumes in the occipital lobes between the two groups was performed using voxel-based morphometry. Our analysis revealed a regionally specific decrease in grey matter volume at the occipital poles in albinism. The location of the decrease in grey matter corresponds to the cortical representation of the central visual field. This reduction is likely to be a direct result of decreased ganglion cell numbers in central retina in albinism.

Orientational diffusion reflects fiber structure within a voxel

Several new MR techniques have been introduced to infer direction through diffusion in multiple nerve fiber bundles within a voxel. To date, however, there has been no physical model reported to evaluate these methodologies and their ability to determine fiber orientation. In this article a model of diffusion analogous to nerve fibers is presented. Diffusion measurements at multiple closely spaced angles of 15 degrees in samples with different fiber orientations are compared with theoretical calculations for restricted diffusion in cylindrical geometry. Orientational diffusion measurements are shown to reflect fiber geometry and theoretical predictions to within 10%. Simulations of fiber crossings within a voxel suggest fiber orientation does not correspond to the direction of the largest measured diffusion coefficient, but theoretical knowledge of signal decay curves can predict the shape of these diffusion coefficient contours for given fiber orientation probabilities.