Mutual inhibition between olivary cell groups projecting to different cerebellar microzones in the cat.

This study was carried out predominantly on the b zone in the lateral vermis of the cerebellar anterior lobe. This zone is divided into sagittally oriented microzones which receive a somatotopically organized climbing fibre input. It was shown that the climbing fibre input to one microzone is inhibited by stimulation of a nerve that projects to an adjacent microzone. The degree of inhibition was related to the proximity of the microzones involved. The latency of the inhibition was short and the duration 70-110 ms. The inhibition of climbing fibre responses occurred in the inferior olive and was presumably due to post-synaptic inhibition of the olivo-cerebellar neurones. The mutual inhibition could be produced by antidromic activation of olivo-cerebellar neurones. An inhibition with similar properties as in the b zone, but weaker, was observed between forelimb and hindlimb inputs to the c1 and c3 zones in the pars intermedia. In the c3 zone, an inhibition between adjacent forelimb microzones also occurred.