The Ontogeny of Associative Cerebellar Learning

Ontogenetic changes in associative cerebellar learning have been examined extensively using eyeblink conditioning in infant humans and rats. The cerebellum is essential for eyeblink conditioning in adult and infant animals. The cerebellum receives input from the conditional stimulus (CS) through the pontine mossy fiber projection and unconditional stimulus (US) input through the inferior olive climbing fiber projection. Coactivation of the CS and US pathways induces synaptic plasticity in the cerebellum, which is necessary for the conditional response. Ontogenetic changes in eyeblink conditioning are driven by developmental changes in the projections of subcortical sensory nuclei to the pontine nuclei and in the inhibitory projection from the cerebellar deep nuclei to the inferior olive. Developmental changes in the CS and US pathways limit the induction of learning-related plasticity in the cerebellum and thereby limit acquisition of eyeblink conditioning.