The maturation of cutaneous reflexes studied in the upper limb in man.

Cutaneous reflex responses have been recorded from forearm flexor and extensor muscles following electrical stimulation of the fingers. Recordings have been made from premature infants, term infants and children between the age of 6 weeks and 11 years. In the new-born, stimulation of the fingers elicits such a powerful reflex that, in general, individual stimuli will evoke a reflex synchronous action potential in both forearm flexor and extensor muscles. Individual stimuli delivered to the fingers also elicit reflex synchronous muscle action potentials in forearm flexor and extensor muscles in patients with clinical signs of upper motor neurone lesion affecting the upper limb; this has not been observed in normal adult subjects. The latency of the reflex response in the term infant is about 18 msec. Comparison of this value with the latency of the tendon jerk for these muscles would indicate a central delay for the cutaneous reflex of about 3 msec. The latencies of the cutaneous reflex and tendon jerk remain constant over the first 5 years of life. The size of the short-latency cutaneous reflex response decreases progressively over the first year of life. In the second year of life stimulation of the fingers produces long- as well as short-latency increases in recorded muscle electrical activity. The maturation of the cutaneous reflex response is discussed in terms of the maturation of function of the corticospinal tract.