The 'amygdala theory of autism' revisited: linking structure to behavior.

The 'amygdala theory of autism' suggests a crucial role for the amygdala in the neurobiological basis of autism spectrum disorders. However, to date evidence is lacking of a direct relationship between amygdala measures and behavioral manifestations of autism in affected individuals. In 17 adult individuals with Asperger syndrome (AS) and 17 well-matched controls we therefore assessed associations between MRI-derived amygdala volume and behavioral variables of emotion recognition and social cognition, as well as with core AS symptomatology. Results revealed that individuals with AS exhibited impairments in emotion recognition and social cognition compared to controls and also showed atypical relationships between amygdala volumes and overall head size. We found positive associations between emotional and social understanding and amygdala volume in the control group, but not in the AS group. In the AS group however, amygdala size was negatively related to diagnostic parameters, with smaller amygdala volumes involving higher levels of restricted-repetitive behavior domains. Our data seem to indicate that in AS the amygdala is not crucially involved in social and emotional understanding. It may, however, be a mediator for narrow interest patterns and the imposition of routines and rituals. Our data, in conjunction with current literature, seem to argue for a modification of the 'amygdala theory of autism'.