The functional neuroanatomy of social behaviour

The functional
Facial expressions help shape behaviour, and we investigated if high-functioning people with autistic disorder show neurobiological differences from controls when processing emotional facial expressions. We used functional MRI to investigate brain activity in nine adults with autistic disorder when explicitly (consciously) and implicitly (unconsciously) processing emotional facial expressions. Subjects with autistic disorder differed significantly from controls in the activity of cerebellar, mesolimbic and temporal lobe cortical regions of the brain when processing facial expressions. Notably, they did not activate a cortical ‘face area’ when explicitly appraising expressions, or the left amygdala region and left cerebellum when implicitly processing facial expressions. High-functioning people with autistic disorder have biological differences from controls when consciously and unconsciously processing facial emotions, and these differences are most likely to be neurodevelopmental in origin.

Subjects
We studied nine high-functioning adult male volunteers [mean age ± standard deviation, 37 ± 7 years; FSIQ (full scale IQ) 102 ± 15] clinically diagnosed, using ICD-10, as having Asperger’s syndrome (seven subjects ) or autism (two subjects).

Discussion
Because high-functioning people with autism have social deficits despite the preservation of explicit intellectual skills, we explored which brain area mirrored this dissociation (i.e. we determined where activity during the explicit task did not significantly differ between the controls and autism group but was significantly different during the implicit task). The amygdalohippocampal junction and left cerebellum showed this pattern of activity. Previous studies of healthy controls reported that the amygdala region is active during the implicit processing of expressions, also, the amygdala is implicated in normal social and emotional behaviour and in the learning and representation of the motivational meaning of stimuli. Thus, dysfunction of the amygdolohippocampal complex may partially explain some of the social deficits in people with autism. Also, studies of people with autism have reported abnormalities in the distribution of pyramidal cells in the medial temporal lobe, amygdala enlargement and functional abnormalities in amygdala activity during a theory of mind task. Thus, the amygdala region may form an important part of the pathogenic substrate of autism. However, our findings also suggest that people with autistic disorder have functional abnormalities in other brain regions when processing facial expressions, including the right fusiform gyrus, early sensory cortices, insula and cerebellum.