COMPARISON OF SINGLE MOTOR UNIT RESPONSES TO TRANSCRANIAL MAGNETIC AND PERONEAL NERVE-STIMULATION IN THE TIBIALIS ANTERIOR MUSCLE OF PATIENTS WITH AMYOTROPHIC-LATERAL-SCLEROSIS

Responses of single tibialis anterior motor units to transcranial magnetic stimulation and to a synchronized Ia volley evoked by peripheral nerve electrical stimulation were obtained in amyotrophic lateral sclerosis (ALS) patients and normal controls. Whereas the units of normal subjects exhibited rather stereotyped short-latency spike density peaks in response to both types of stimulus, the responses of ALS patient units were much less uniform. All ALS patient units exhibited a response to the synchronized Ia volley indistinguishable from that of normal subjects, indicating that the investigated spinal motoneurons are capable of normal excitatory responses in ALS patients. More than half of the ALS patient units responded to the transcranial magnetic stimulus with prolonged spike-density peaks appearing at a latency consistent with the notion that these pathological peaks are evoked by some relatively hyperexcitable structures presynaptic to the corticomotoneurons.