Transcranial Magnetic Stimulation Modulates P300 Indices of Selective Attention In Autism

Background: Autism Spectrum Disorder (ASD) has been previously shown by our group to be associated with abnormalities in later-stage event-related potential (ERP) indices of selective attention. Specifically the attention-orienting frontal P3a and the sustained attention centro-parietal P3b have been found to be atypical in ASD during a visual oddball task; this may be related to reduced inhibitory tone of the dorsolateral prefrontal cortex (DLPFC) in ASD, as the DLPFC has been associated with selective attention and working memory.

Objectives: In this study we wanted to test the effects of bilateral low frequency repetitive transcranial magnetic stimulation (rTMS) applied to the dorsolateral prefrontal cortices on novelty processing in ASD. We hypothesized that rTMS would improve cortical inhibitory tone by selectively activating inhibitory GABAergic double bouquet interneurons, and this would improve task performance.

Methods: We recruited 25 participants with ASD and randomly formed a 15 subject active-TMS group and a 10 subject wait-list group. We assessed task performance before and after twelve sessions of bilateral low frequency rTMS in the active TMS group and before and after a six week waiting period in the waitlist group.

Results: Individuals with ASD showed significant improvement following treatment evidenced by improved P3b responses to targets and better stimulus discrimination. There was also a significant improvement in frontal reactivity to novelty as indicated by the P3a component. The wait-list group did not show any significant changes.

Conclusions: We propose that that low-frequency rTMS may have increased cortical inhibitory tone and subsequently improved performance in the novelty processing task. TMS has the potential to become an important therapeutic tool in ASD treatment with few, if any side effects.