Re-Examining the Brain and
Autism
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.
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