Functional variation in dermatomes in the macaque monkey following dorsal root lesions

Previous definitions of dermatomes, in various species, have revealed a characteristic pattern of serial overlapping root areas. Most investigators have used either the method of “remaining sensibility” or recordings of dorsal nerve root potentials, and have sectioned the dorsal nerve roots within the spinal canal, proximal to the dorsal root ganglia. We have used the method of “remaining sensibility” in experiments in macaque monkeys. Section of the neighboring dorsal roots proximal to their ganglia produced dermatomes which resembled closely those isolated by Sherrington. However, we found consistently that when the neighboring spinal nerves were sectioned distal to their dorsal root ganglia, the isolated root areas on the trunk were approximately twice as large as before and now also showed persistent hyperesthesia. Re‐sectioning of the dorsal roots of these nerves within the dura reduced the isolated root areas to their “classical” size, but usually only after a delay of three or four days. The injection of subconvulsive doses of strychnine sulfate solution produced an enormous expansion of an isolated dermatome, irrespective of whether the neighboring roots had been sectioned intradurally or beyond their ganglia; no change in area was observed after the injection of morphine sulfate solution. Conversely, the size of a dermatome which had been isolated by intradural section of three dorsal roots above and below was reduced by subsequent section of three additional roots above and below. We have concluded that the observed size of an isolated dermatome is a variable quantity and can be taken as an index of the efficiency of sensory transmission within the same and neighboring segments of the spinal cord.