Inhomogeneous Somatic Maps in Autism

Background: Current research points to a deficit in connectivity in the brains of individuals with autism. There has been more progress on functional long-range connectivity between different brain areas in autism than on local connectivity within a brain area. Studies have focused on the neural basis of “core characteristics,” particularly social-emotional differences in autism. The comorbidity of diverse impairments such as sensorimotor differences and social-emotional deficits suggests that abnormalities in brain development of a more general nature such as differences in local and long-range circuitry affect multiple different functions.

Objectives: We explored somatic maps in AD as reflective of abnormalities in circuitry.

Methods: Using magnetoencephalography (MEG), we examined the cortical response to tactile stimulation of the thumb (D1) and index finger (D2) of the dominant hand and lip of young adult observers (18 individuals with autism disorder or ADs and 17 typically developing persons or TDs). Automatically fitting a single current source model to the evoked potential data, we obtained the cortical representation corresponding to each body part stimulated.

Results: The somatic maps revealed two differences. i) The distance between the representations in cortex of D1 and the lip was significantly larger in ADs compared with TDs (p < 0.001). The difference was significant, even after normalizing by head volume. ii) Typically, D2 is farther from the lip than is D1. This was reversed in ADs. The ratio of the distance of each finger from the lip was significantly different between the two populations.

Conclusions: The twin findings of atypical somatic map extent in autism reflect atypical local connectivity. Synchronous development of a larger head with the stabilization of a somatic cortical map during early childhood in ADs could have left behind an inhomogeneous somatic map. The present findings are a functional imprint of past reports of abnormal anatomy and morphology in autism.