Two forms of short-interval intracortical inhibition in human motor cortex.

Background: Pulses of transcranial magnetic stimulation (TMS) with a predominantly anterior-posterior (AP) or posterior-anterior (PA) current direction over the primary motor cortex appear to activate distinct excitatory inputs to corticospinal neurons. In contrast, very few reports have examined whether the inhibitory neurons responsible for short-interval intracortical inhibition (SICI) are sensitive to TMS current direction.

Objectives: To investigate whether SICI evaluated with AP and PA conditioning stimuli (CS and CS) activate different inhibitory pathways.