The refractory and supernormal periods of the human median nerve.

While the excitability changes which follow a propagated nerve impulse have been the subject of numerous studies in animals, there have been few references to this subject in man. An attempt to study the refractory period of the human ulnar nerve was made by Wagman and Flick (1951), but as recordings were made from the hypothenar muscles rather than from the nerve itself, the results are difficult to interpret. Krnjevic, Kilpatrick, and Aungle (1955) applied pairs of shocks to the ulnar nerve at the wrist, and investigated the least interval at which a response to the second shock could be recorded from the nerve at the elbow; only two subjects were examined and no estimate of the relative refractory period was made. Brown (1960) also used stimulation of the ulnar nerve at the wrist with recording at the elbow in four subjects, and noted that the recovery of normal responsiveness was followed by transient supernormality. In the present work we have studied the refractory and supernormal periods of the human median nerve with stimulation at the wrist, action potentials being recorded from the nerve above the elbow by a technique similar to that originally described by Dawson and Scott (1949). A briefpreliminaryaccount of this work has been published elsewhere (Gilliatt and Willison, 1962). METHODS Four healthy subjects were used, their ages ranging from 20 to 40 years. Most of the experiments were carried out on two subjects (R.W.G. and R.G.W.) but the main results were confirmed in the other two subjects as well. Before each experiment the subject sat with both arms in hot water to above the elbows for five or 10 minutes. He then lay covered with blankets on a couch, with the arm under examination wrapped in several layers of cotton wool. When these precautions were taken skin temperature, which was measured by a thermistor close to the stimulating cathode, remained above 35°C. throughout experiments lasting up to one hour; no 'Clinical research fellow, M.R.C. experiments are included in the present series in which skin temperature fell below 35°C. Two stimuli of independently variable intensity were delivered through a single cathode over the median nerve at the wrist. The stimulus interval could be varied in 0-1 msec. steps from 0 to 1 I-0 msec. and in 1 msec. steps for intervals longer than this. Each stimulus was a condenser discharge with a rapid rise-time, the decay having …