CROSSED REDUCTION OF HUMAN MOTOR CORTEX EXCITABILITY BY 1-HZ TRANSCRANIAL MAGNETIC STIMULATION

Electrophysiological studies have shown that 1-Hz repetitive transcran ial magnetic stimulation (rTMS) of the primary motor area (M1) can pro duce a local decrease in excitability. Functional imaging data suggest that this change may be bilateral. In normal subjects, we measured mo tor evoked potential (MEP) amplitude at a series of stimulation intens ities in the contralateral M1 before and after 15 min of active or sha m rTMS at just above the MEP threshold. The slope of the curve relatin g MEP amplitude and stimulation intensity was decreased in the unstimu lated hemisphere by active but not sham rTMS. This demonstrates that r TMS can condition cortical excitability at a distance of one or more s ynapses and suggest that decreased excitability to TMS is a correlate of decreased blood flow and metabolism. (C) 1998 Elsevier Science Irel and Ltd. All rights reserved.