Effects of low and high frequency repetitive transcranial magnetic stimulation of the primary motor cortex on contingent negative variations in normal subjects.

The state of primary motor cortex (M1) excitability is crucial for the processing of voluntary movement. We aimed to test the modulation induced by 1 Hz and 5 Hz repetitive transcranial magnetic stimulation (rTMS) of M1 on both early and late components of the contingent negative variation (CNV) and on the motor reaction in normal subjects. The CNV was evaluated in basal, and after 15 min of real or sham 1 Hz and 5 Hz stimulation of the left motor cortex in 7 right handed volunteers. Inhibition of motor cortex, due to rTMS stimulation, resulted in an amplitude increase of early and late components of CNV, and a slight reducing effect on motor reaction times, while 5 Hz stimulation did not change CNV amplitude. In normal subjects transient inhibition of motor cortex causes an increase of cortical events preceding external-cued voluntary movements, as a probable compensatory phenomena able to maintain an efficient motor performance.