Excitatory and Inhibitory Effects of Transcranial Magnetic Stimulation

This paper reviews the use of transcranial magnetic stimulation (TMS) in investigating intracortical circuits in the primary motor cortex (M1). TMS is a noninvasive and painless method of stimulating the human brain and has become a widely used technique in neurophysiology and neurology. When TMS is applied to the M1, it generates a motor evoked potential (MEP) in the target muscles. TMS also activates different intracortical circuits within the M1 and connections from other cortical areas to the M1. These intracortical circuits interact with each other. Abnormalities in these circuits are found in neurological and psychiatric disorders and studies of these circuits are useful in understanding the pathophysiology of these conditions.