When Is a Face a Boat?: An fMRI Study In Category Perception In ASD

Background:  

Many studies in the adult brain have shown distinct neural regions responding to visual stimuli such as faces, houses, letters, numbers, and objects. Deficits in face processing, both behaviorally and neutrally, have been observed in individuals with an autism spectrum disorder (ASD). However, there has been comparatively little research on the brain activity evoked by the other stimulus categories.

Objectives:  

Using fMRI, we aim to establish comprehensive maps of visual perception using a broad range of visual stimuli within a single experiment. 

Methods:  

Adults (n=23 adults), children with an ASD (n=22) and their unaffected siblings (n=27) were scanned during a passive viewing experiment consisting of visually presented black and white faces, houses, objects (vehicles in this case), letters, and numbers—unaffected siblings and adults were used as control groups. Regions of interest were constructed using pairwise contrasts and groups were compared on the extent of activation, and the magnitude and location of the peak of activation within each region. 

Results:  

When compared to adult controls, all groups of children had less localized and more diffuse activations in response to all categories. Unaffected siblings appeared to have the most differential activation in every category. Children with ASD had some differential activation also; the highest activations were found when viewing houses. There was little differential activation between either faces and objects or houses and objects. Areas that were consistent across groups and between adults and children with ASD tended to be areas corresponding to more general spatial skills, such as the posterior cingulate cortex. Neither child group showed any differentiation between numbers and letters.

Conclusions:  

While there was some overlap between adult and child areas, many of the localized areas were different, perhaps indicating a shift in some visual processing systems. Relative to their unaffected siblings, children with an ASD showed the least impairment in processing houses, though even this seems to activate areas of general spatial orientation, such as the posterior cingulate cortex, as opposed to areas of visual perception, such as the parahippocampal place area. In addition, the lack of differentiation between categories suggests that there is a serious deficit in category formation in general. Studies such as these can help shed light on the developmental theories of ASD—the neurobiological causes of these deficits (such as lack of pruning) remain to be seen.