Translational Approach to Behavioral Learning: Lessons from Cerebellar Plasticity

Figure 1

Schematic diagram of the circuits interconnecting the olivocerebellum, the thalamus, the basal ganglia, the pontine nuclei, the cerebral cortex, and the spinal cord. The part of the circuit showing anatomical links between the basal-ganglia and the cerebellum is adapted from recent anatomical experiments using retrograde transneuronal transport of rabies virus from injections into the cerebellar cortex and in nuclei of basal ganglia, establishing evidence for disynaptic pathways that directly link the cerebellum with the basal ganglia (see [1] for a review). Injection of the rabies virus into the cerebellar cortex induced two stages of transport: retrograde transport to first-order neurons in the pontine nuclei (PN) that innervate the injection site and then retrograde transneuronal transport to second-order neurons in the subthalamic nucleus (STN) that innervate the first-order neurons [28]. Injection of rabies virus into the striatum (STR) induced retrograde transport to first-order neurons in the thalamus (TH) that innervate the injection site and then retrograde transneuronal transport to second-order neurons in the dentate nucleus (DN) that innervate the first-order neurons [29]. In addition, the striatal neurons that receive cerebellar inputs include neurons in the “indirect” pathway that send projections to the external globus pallidus (Gpe). The classical network of the basal ganglia (adapted from [30]) represented by the parallel “direct” and “indirect” pathways from the STR to the basal output nuclei. The “direct” path sent inhibitory input from the SRT to the internal part of the globus pallidus (Gpi). The basal ganglia circuit is completed by the dopaminergic pathway and represented the projection of the substantia nigra pars compacta (Snpc) to the STR. Inhibitory neurons are shown as filled symbols, excitatory neurons by open symbols. Grey and white arrows represent inhibitory or excitatory pathways, respectively. Abbreviations: PC, Purkinje cell; GO, Golgi cell; DCN, deep cerebellar nuclei; PF, parallel fiber; GC granule cell; IO, inferior olive; CF, climbing fiber.