SIMULTANEOUS RECORDING OF SLOW BRAIN POTENTIALS AND TRANSCRANIAL MAGNETIC STIMULATION OF HAND AREA IN HUMAN MOTOR CORTEX

Recording of slow brain potentials (SPs) and transcranial magnetic sti mulation (TCMS) of the human motor cortex were combined to probe the r elationship between SP level and excitability of cortical neurons. In experiment 1, TCMS was applied during and shortly after the warning in terval in a forewarned reaction time task. Electromyographic (EMG) res ponses to TCMS increased only slightly during the warning interval and were significantly elevated 150 ms after the imperative stimulus. In experiment 2, TCMS was applied during biofeedback-induced cortical pos itivity and negativity. In this non-motor task a dependence of TCMS re sponse on SP amplitude was not significant. Results indicate higher lo cal excitability of motor cortex during cortical negativity when a pre paratory motor task is required. TCMS may better be suited to probe pr ocesses involved in motor tasks rather than non-motor and cognitive co nditions.