Pathological plantar response. I. Flexor and extensor components in early and late reflex parts.

In previous investigations (Kugelberg, Eklund, and Grimby, 1960; Grimby, 1963a, b) the spinal part of the human plantar reflex in normal and pathological cases was studied by means of electromyographic techniques. Special attention was paid to the reflex patterns obtained during simultaneous recordings from the short hallux flexor and extensor, since the strength of the electrical response in the flexor proved to be a sensitive index of the tendency to plantar flexion, and the response in the extensor to the tendency to dorsiflexion of the hallux. In normal subjects flexor activity is strongly predominant in the reflex pattern, and it was assumed that the suprasegmental control system could discriminate among the available types of reaction, selecting that best serving a protective function. In pathological cases extensor activity may be predominant. In some cases the reflex pattern obtained on stimulation of the plantar surface of the foot may consist of an early part predominantly extensor, and a late part predominantly flexor in type. In other cases it may consist of an early part predominantly flexor and a late part predominantly extensor in type. It was assumed that both these components are transmitted in such a way that one may be affected by the pathological process independently of the other. The purpose of the present investigation was to study why in pathological cases the extensor activity in the plantar response, viz., the deviation from normal, may sometimes be limited to the early, and sometimes to the late, part of the reflex pattern.