Motor-evoked potentials are facilitated during perceptual identification of hand position in healthy subjects and stroke patients

Objective: To delineate the facilitatory and/or inhibitory influence of relevant and irrelevant sensory afferent information to the motor cortex. The study is based on the assumption that sensorimotor coupling is crucial for motor learning and recovery. Design: The interaction of a standard transcranial magnetic stimulus (TMS) with the facilitatory and/or inhibitory influence that proprioceptive afferent information exerts on the motor cortex was investigated. Setting: A neurological rehabilitation hospital. Subjects: Sixteen healthy subjects and 14 stroke patients. Main outcome measures: Amplitudes and latencies of motor-evoked potentials (MEPs) recorded from the extensor carpi radialis muscle. The influence of a sensory discrimination task was compared with the influence of a sensory input irrelevant for the task and to a verbal memory task. Recordings were taken after the hand had been moved passively in one of four different positions. Results: In the first trial, TMS was applied without any demand on the subjects. In the second trial, subjects were asked to identify the respective hand position and in the third trial a noun presented at a respective hand position had to be memorized and reproduced after TMS. The sensory discrimination task exerted by far the most prominent facilitatory effect on MEP amplitudes and latencies. An unspecific, albeit reproducible influence on MEP amplitudes was observed when a noun presented at a respective hand position had to be remembered. Conclusions: Using a neurophysiological approach the study demonstrates that a sensory discrimination task based on relevant afferent information to motor centres of the brain forms a prominent facilitatory intervention for those muscle groups that are involved in the task. This holds true for healthy subjects and for hemiparetic stroke patients.