Influence of the corticospinal tract on the cutaneous silent period: a study in patients with pyramidal syndrome.

The cutaneous silent period (CSP) is a brief transient suppression of the voluntary muscle contraction that follows a noxious cutaneous nerve stimulation. In this study we investigated the influence of the corticospinal tract on this spinal inhibitory reflex. In patients with pyramidal syndrome and in a group of healthy subjects we delivered painful electrical finger stimulation during sustained contraction of the ipsilateral abductor digiti minimi muscle. The CSP latency and duration and the background electromyographic (EMG) activity were measured and compared between-groups. The compound motor action potential amplitude and F-wave latency were also measured after electrical stimulation of the ulnar nerve at the wrist. The CSP latency was significantly longer in patients than in healthy subjects. None of the other variables differed in patients and healthy subjects. Our findings suggest that corticospinal projections influence the CSP latency probably by modulating the balance of excitability in the underlying circuits.