Transmission of Predictable Sensory Signals to the Cerebellum via Climbing Fiber Pathways Is Gated during Exploratory Behavior

Pathways arising from the periphery that target the inferior olive (spino-olivocerebellar paths, SOCPs) are a vital source of information to the cerebellum and are modulated (gated) during active movements. This limits their ability to forward signals to climbing fibers in the cerebellar cortex. We tested the hypothesis that the temporal pattern of gating is related to the predictability of a sensory signal. Low intensity electrical stimulation of the ipsilateral hindlimb in awake rats evoked field potentials in the C1 zone in the copula pyramidis of the cerebellar cortex. Responses had an onset latency of 12.5±0.3 ms and were either short or long duration (8.7±0.1 ms versus, 31.2±0.3 ms, respectively). Both types of response were shown to be mainly climbing fiber in origin and therefore evoked by transmission in hindlimb SOCPs.

Changes in response size (area of field, mV.ms) were used to monitor differences in transmission during rest and three phases of rearing: rearing up (phase 1), upright (phase 2) and rearing down (phase 3). Responses evoked during phase 2 were similar in size to rest, but were smaller during phases 1 and 3 i.e. transmission was reduced during active movement when self-generated (predictable) sensory signals from the hindlimbs are likely to occur. To test whether the pattern of gating was related to the predictability of the sensory signal some animals received the hindlimb stimulation only during phase 2. Over about 10 days the responses became progressively smaller in size, consistent with gating-out transmission of predictable sensory signals relayed via SOCPs.