Neural development in children: a neurophysiological study

In adult human subjects torque motor imposed angular displacements of the upper limb joints result in two major reflex EMG components as identified by their latency. The shorter latency (SL) component is probably the spinal stretch reflex and the longer latency (LL) reflex component may involve supraspinal structures. Tendon jerk, arising via the spinal reflex pathway, is present in children at birth. In this study the presence and the development of the LL component in wrist flexors was investigated in children between the ages of 2 and 13 years. Kinaesthetic reaction times were tested simultaneously. In young children, the duration of the LL component was much longer than that in adults. The duration decreased slowly from 2 to 6 years, following which a relatively abrupt decrease between the ages of 6 and 8 years took place. After 8 years of age responses looked more adult-like. Kinaesthetic reaction times attained adult-like values after 10 years of age. Various possibilities underlying these observations are discussed.