Maturation of the cutaneomuscular reflex recorded from the first dorsal interosseous muscle in man.

1. Cutaneous reflexes have been recorded from the first dorsal interosseous muscle following electrical stimulation of the digital nerves of the index finger in man. Recordings have been obtained from 127 children, aged from 3 to 18 years while each performed an isometric abduction of the index finger and whole hand grips. 2. In the adult, reflexes recorded while subjects performed an isometric abduction of the index finger consisted of three readily identifiable components within the first 100 ms. These were an initial short spinal latency increase in EMG (E1), followed by a decrease (I1), followed by a prominent longer-latency increase (E2) which was normally larger in size than the shorter-latency increase. 3. The configuration of the reflex changed during development. When recorded during an abduction, the E1 component was present in all children and showed a small but progressive reduction in size with age. With increasing age, both the I1 and E2 components were present in an increasing proportion of children and increased in size until the adult configuration was reached at 14-15 years. 4. Comparison of reflexes recorded during sustained whole hand grips with reflexes recorded during an isometric index finger abduction revealed differences in all three components. When recorded during those grips used in the present study the E1 component was generally significantly larger while the I1 component was generally significantly smaller than when recorded during index finger abduction. At all ages the E2 component was significantly smaller when recorded during a grip. 5. The configuration of the reflex during an isometric index finger abduction was compared with the ability of the child to perform rapid finger movements. Those children who had no E2 component tended not to perform well in the tests of rapid finger movement. However, there was no simple relationship between the size of the E2 component and ability to produce rapid finger movements.