Building a Selective Inhibitory Control Tone in Autism: An rTMS Study

University Of Louisville, Louisville KY

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Abstract

Autism is a pervasive developmental disorder of childhood characterized by deficits in social interaction, language, and stereotyped behaviors and restricted range of interests. Recent studies on postmortem tissue suggest that autism is associated with cortical cytoarchitectural abnormalities. In brief, reports on independent populations have shown a reduction in the neuropil space at the periphery of the minicolumn. This is the compartment where lateral inhibition sharpens the borders of minicolumns and increases their definition. The primary source of for this inhibitory effect is derived from axon bundles of double-bouquet cells. The axons of double bouquet cells arrange themselves in essentially repeatable patterns varying between 15 ?m and 30 ?m wide, perpendicular to the cortical surface. This grant attempts to preferentially strengthen the inhibitory surround of minicolumns by taking advantage of the geometry of double bouquet cells. We will use the principle of induction to induce electrical currents in double bouquet cells by applying a coil of wire energized by a capacitor (Transcranial Magnetic Stimulator or TMS) to provide a magnetic field orthogonal to the plane of the coil. Slow or low frequency TMS will enhance interneuron inhibition which in turn will enhance spatial contrast needed to optimize functional discrimination in minicolumnar units. The trial will recruit 70 autistic patients and 30 controls matched for age, sex, IQ, and socio-economic class. Outcome measures will include behavioral and electrophysiological measures. Overall, our project will link behavioral, clinical, and neurophysiological (qEEG, ERP) responses during cognitive tests and TMS treatment outcomes with an underlying neuropathology model (minicolumnar pathology and lateral inhibition deficits) derived from investigations in our laboratory. The results of the proposed study will help understand the specific social communication and cognitive deficits associated with developmental abnormalities of functions within cortical circuitry, and thereby contribute to understanding the brain substrates of behavioral dysfunctions typical for autism. The proposal represents a new development in combining TMS with functional outcome measures (cognitive ERP, EEG), using TMS as a theory-guided psychiatric therapy in autism.