Autism spectrum disorders or pervasive developmental disorders involve impairments in reciprocal social interactions as well as restricted repetitive patterns of behavior in the absence of obvious intellectual dysfunction. Even though the exact pathophysiology of autism remains to be established, it has been widely accepted that this condition strongly impact central nervous system function. Of the brain structures that have been proposed to play a crucial role in the neurobiology of the clinical features of autism, the contribution of the amygdala is particularly convincing. It is the impairments of autistic individuals to process emotional and social information that has left many health care professionals to hypothesize an association of the amygdala and autism.

Brain imaging studies show abnormalities in the amygdala in affected individuals. Conversely, most neuropathological results were non-specific and brain volumetric studies have been, for the most part, inconsistent. More significantly, researches assessing the participation of the amygdala failed to report associations with autism related behavioral and emotional impairments. Information on such correlations would be specifically supportive in providing information on whether the amygdala dysfunction is relevant to the etiology of autism; that is if they are indeed accurate pathophysiological mediator of autism.

Functional neuroimaging involving autistic individuals show less amydgala activation when inferring mental states, interpreting facial emotional expressions or in response to changing task demands in a mental task (Wang et al., 2004), as compared to normal persons.

Presently, no efforts have been made to determine the relationship between the amygdala to the diagnostic features of autism spectrum disorders according to the criteria in the Diagnostic and Statistical Manual of Mental Disorders version IV (DSM-IV) and the International Classification of Diseases version 10 (ICD-10). Although autistic symptomatologies include impairments social cognition and emotion recognition, which are representative of a diagnostic cluster in DSV-IV and ICD-10, they are not fundamental parts of the psychiatric diagnosis of autism.

A study investigated the direct relationship between amygdala function and autism in affected individuals (Dziobek et al., 2005). Patients with autism and normal controls were examined using brain imaging techniques derived amygdala volume and behavioral factors of emotion and social functioning and results of both groups were then compared to gain insight on the association between these to variables. Results show that patients with autism manifested dysfunction in emotional and social functioning as compared to normal individuals. They also showed an uncharacteristic association between amygdala volumes and overall head dimension. Positive associations were found between social and emotional understanding and amygdala volume in unaffected individuals, but this was not the case in patients with autism. Interestingly, when correlating amygdala volume with general brain size for the groups separately, there was a significant positive trend for normal individuals, while there was only a weak negative association in autistic patients. Volumetric analyses did not yield significant differences between the groups. Results indicated that in autism, the amygdala is not a key mediator for social and emotional functioning.

In general, clinical and experimental studies fail to provide clear-cut evidence to conclude that the amydala is indeed a major pathology in autism. Further research is deemed necessary to support significance of amydala dysfunction in pervasive developmental disorders.