This is an individual National Research Service Award for post-doctoral research training, which provides support for promising Fellowship Applicants with the potential to become productive, independent investigators in scientific health-related research fields. Recent findings in neuroscience suggest that individuals with autism spectrum disorder (ASD) have significantly more intracortical white matter (connections) in their brain, especially in frontal regions. The current proposal seeks to extend this finding and investigate whether the reported overconnectivity may lead to enhanced plasticity (the ability of the synapse between two neurons to change in strength) in these individuals which may account for some of the symptoms seen in ASD, including echolalia, echopraxia, and savant skills. Non-invasive transcranial magnetic stimulation (TMS) will be used to evaluate plasticity of the cerebral cortex by measuring the motor evoked potential (MEP) both before and after experimental manipulations. Enhanced plasticity of cortical connections may provide a neural mechanism underlying the behavioral symptoms which characterize ASD. Additionally, in conjunction with other studies, it is hoped that the information gained by this study may lead to the development of novel therapeutic strategies to treat the underlying cause of the disorder rather than the behavioral symptoms.