Electromyographic study of polysynaptic responses from muscles not supplied by the stimulated nerve: preliminary report.

15 subjects with normal neurological examinations, 7 hemiplegic patients, 5 patients with dementia and 4 with Parkinsonism were examined. A 1msec duration pulse below the pain threshold was applied to the median and ulnar nerves at the elbow and wrist. The activities of the biceps, triceps, flexor carpi radialis, forearm extensors and abductor pollicis brevis were recorded with surface electrodes. The most frequently observed response in normal subjects and hemiplegic patients occurred in the biceps, and had a latency of about 30msec. The other frequently elicited response in normal subjects and hemiplegic patients was in the forearm extensors. Recovery curves were obtained for the biceps response. A significant difference between normal subjects and hemiplegic patients was found. In the patients suffering from Parkinsonism, as well as in demented patients, one could record easily polysynpatic reflexes from other forearm muscles. This suggests the presence of basal ganglia damage in atrophic dementias.