[Evaluation of brain function: electrophysiology of the motor system]

To evaluate brain motor function, transcranial magnetic stimulation and supraspinal control of spinal reflexes are reviewed. Motor evoked potentials (MEPs) is facilitated after movement, depending on muscles (arm, hand) and movements (isometric, precise, repetitive, sequential), which indicates specialization of cortical mechanisms. EMG triphasic pattern in ballistic movement is delayed by magnetic stimulation, but the pattern itself is preserved. Ballistic and associated posture-adjusting movements are delayed by magnetic stimulation in the same way, and similar cortical mechanisms appear to be included. Patients with motor neglect, normal MEPs and remarkably prolonged silent period show inability to initiate movement for several seconds after magnetic stimulation, and strong and long-lasting intracortical inhibition are observed. Motor neglect can be produced by strong inhibitory inputs to the motor cortex. Neural plasticity is studied in patients with brain and peripheral lesions; ipsilateral MEPs, enlargement of muscle representation in the cortex, and contribution of descending pathways other than corticospinal tract are reported. Central control of spinal reflex activities is also important in motor control. Reflex circuits contribute to reciprocal inhibition and to selective contraction, or function as an attenuator of activity of the motoneurone pool. Neural plasticity after daily exercise is reported also at the segmental level.