Gating in the spino‐olivocerebellar pathways to the c1 zone of the cerebellar cortex during locomotion in the cat.

Abstract

1. The field potentials evoked in the cerebellar cortical c1 zone by single-pulse, non-noxious stimulation of the superficial radial nerve have been recorded with tungsten-in-glass microelectrodes in awake cats. Responses that were due to transmission in the spino-olivocerebellar pathways (SOCPs), which terminate in the cortex as climbing fibres, were identified and studied while the cat walked on a moving belt. 2. The size of the climbing fibre-evoked potentials varied systematically during the step cycle. They were invariably largest in mid- to late swing of the ipsilateral forelimb and, at most recording sites (5/6), they were smallest during the first half of stance. 3. With low stimulus strength, the probability of evoking a measurable response also varied. The probability was greatest in mid- to late swing and least in early stance. 4. Similar variations were shown to occur when the analysis was restricted to responses evoked by a single functionally homogenous SOCP, the dorsal funiculus SOCP. 5. It is proposed that these variations reflect the operation of a gating mechanism which modulates the excitability of the SOCPs and prevents them transmitting self-generated tactile inputs to the cerebellum while facilitating transmission when unexpected inputs are most likely to arise. 6. The present data are compared with those from a similar study of the c2 zone SOCPs (Apps, Lidierth & Armstrong, 1990) and are discussed in relation to a study of the effects of unexpected mechanical perturbations of stepping (Andersson & Armstrong, 1987).