Development of cerebellar somatosensory evoked potentials in the rat.

In lobule VIa of the vermis cerebelli of 69 male albino rats aged from 7 to 90 days we studied the somatosensory potential evoked by electrical stimulation of the sciatic nerve. A response consisting of a marked positive wave and a small negative wave was constantly present in the group of 9- to 10-day-old animals. At the end of the second week, an initial negative wave appeared. The response of 18-day-old animals consisted of 5 waves of alternating polarity and started with a small positive wave as in adult rats. During subsequent development only the relative size of the individual components changed, the later negative wave, N2, being the most marked component in adult animals. An attempted explanation of the possible origin of evoked potentials in young animals, based on the available data on the morphological development of the cerebellar cortex, is submitted. The latent periods, measured to the maxima of the individual waves, shorten abruptly between the 10th and 20th day and then undergo little change. Greater fatigability of the responses of young animals can be demonstrated by using rhythmical stimulation and paired stimuli. Somatosensory responses appear sooner than visual evoked potentials in the cerebellum, but they develop later than somatosensory evoked potentials in the cerebral cortex.