Electrophysiological study of the Babinski sign in paraplegic patients.

The physiopathology of the Babinski sign was investigated electrophysiologically in patients with spinal cord lesions. The stimuli were delivered via a blunt probe. The force exerted perpendicular to the plantar surface and the forward displacement of the probe were measured. The responses were recorded by surface electromyography of the Extensor Digitorum Longus and Flexor Hallucis Brevis. The latencies of the responses were 160-500 ms. The shortest latencies were observed after strong and fast-increase, moving or static stimuli. The responses to weak, gradual stimulation, appeared at a constant delay after the start of the displacement, equal to the minimum latency. An earlier phasic response was observed after fast-increase stimulations in two subjects. The long latency of the responses is probably due to a long central delay, similar to the late flexion reflex following electrical stimulation.