Neurosystems affected in ASD
Neuroimaging has identified several neural systems that map onto various components of the sympomatology seen in Autism Spectrum Disorders. Arousal, reward, and face processing systems demonstrate the potential utility of neural systems knowledge.
The arousal and reward systems are likely candidates that help a person determine the social significance of stimuli, which is an impairment seen in those with autism. These two systems are likely to be involved in regulating social communication. The facial processing system has also been shown to be abnormal in individuals with ASD, possibly due to reduced experience and subsequently ability in perceptual processing of faces. An eye-tracking study on the social phenotype in autism found that facial processing difficulties were tracked back to difficulties in determining what is socially salient in naturalistic social scenes, which may be caused by abnormal arousal and reward responses to faces in those with ASD. 4
Several fMRI studies have indicated that the amygdala is a signficant contributor to social processing in typically developing participants and to the social processing impairment in autism because of the amygdala's role in arousal processes and its role in emotional stimulus evaluation and detection. One hypothesis is that early amygdala developmental abnormality may cause a chain reaction in brain developmental deficits resulting in social communication impairment.
fMRI studies have also lent support to a hypoactive "emotional brain" with less activation found in the amygdala and fusiform gyrus compared to controls. Another study supporting this idea used eyetracking and fMRI to study gaze fixation duration. They found that when those with autism actively look at a person's eyes, they exhibit hyper activity in the amygdala, suggesting increased arousal during eye contact. Reduced eye contact and gaze aversion may be a strategy to reduce amygdala-driven aversive autonomic arousal. The study also suggests that fusiform gyrus hypoactivity may be a consequence of the autistic group spending less time viewing the eyes compared to controls. Gaze aversion was also seen in unaffected siblings, suggesting that gaze fixation may be a behavioral trait or endophenotype in autism. 5
The behavioral manifestation of abnormal gaze fixation includes high baseline rates of arousal, abnormal arousal habituation rates, sensitivity to sensory stimuli, increased startle from unexpected sounds/speech, and slower habituation to startle relative to controls.5
|Neural System||Area implicated|
|Reward System||Basal Ganglia complex|