Don Rojas, PhD
I. Neuroanatomical Studies of Autism
A large number of MRI-based studies of brain structure in autism have been reported in the past decade, but very few reliable findings have been reported. One problem may be the large heterogeneity of the disorder. We have focused our recent efforts on first-degree relatives of people with autism because such individuals are clinically unaffected, generally have average to above average general cognitive abilities and are not taking medications that may influence the data. In addition, since autism is highly heritable, structural changes we see may point to genetic influences. We have reported that parents of people with autism exhibit larger hippocampi, structures which are critically involved in new learning. In addition, we have recently described structural changes in sensory and motor regions of the brain that are also thought to be important in the ability to infer mental states different from ones one in other people (i.e., theory of mind).
II. Gamma-band abnormalities in autism: MEG studies
It has been proposed that general abnormalities in structural and functional neuronal connectivity may underlie many of the triad of deficits observed in autism. A limited number of deficits at the neuronal level, expressed in multiple neurobehavioral systems could provide substantial explanatory power in autism. For example, abnormal temporal binding and weak central coherence may be related to alterations in brain functional and/or structural connectivity. Gamma band oscillatory activity, as measured using EEG and magnetoencephalography (MEG), has been associated with intrinsic GABAergic activity in animal and computational models of the neocortex and is thought to play an important role in binding and central coherence. We have published data demonstrating that gamma-band activity is abnormal in people with autism (e.g., Wilson et al. 2008), possibly reflecting a cortical GABA dysfunction. The figure below illustrates a time-frequency decomposition of MEG responses from a "virtual electrode" in the auditory cortex, overlaid onto the subject's own MRI based anatomy. The top right hand figure shows the phase-locked power and the bottom right figure shows the inter-trial phase-consistency for the response to a repeated pure tone presentation.