Transcranial magnetic stimulation (IMS), a noninvasive form of brain stimulation, is being developed as aninvestigative and clinical tool for a number of neuropsychiatric disorders. Recently, studies have begunusing IMS to probe the effective connectivity among brain areas- how directly perturbing the activity of agiven brain area affects the activity of other areas. Such studies hold great promise for developing noveldiagnostic and ultimately therapeutic approaches to disorders associated with defective cortico-corticalinteractions, such as schizophrenia and Alzheimer's disease. Fully exploiting this potential requiresunderstanding how IMS activates a cortical target and how that activation propagatesto distant,anatomically connected sites. The proposed research will focus on two novel, complementary strategiesthat should expand our understanding of how IMS induced activity propagates through cortical circuits.The first approach is based on developing a comprehensive analysis of TMS action on cortical circuitsthrough large-scale computer modeling. The second approach uses hd-EEG to experimentally measurepropagation of cortical responses to TMS and how they vary as a function of wakefulness and sleep.
