Translational Approach to Behavioral Learning: Lessons from Cerebellar Plasticity

Figure 2

VOR adaptation and Purkinje cell behavior. (a) Schematic diagram of the circuits connecting the VOR pathway including the medial vestibular nucleus (MVN) and the neural integrator located in the prepositus hypoglossa nucleus (PH) and the horizontal microzone of the flocculus (Floc). The error signal initiated by the retinal slip is conveyed via the inferior olive (IO) by the climbing fiber (CF). The asterisk points to possible sites of VOR plasticity (see text for details). (b) Peristimulus time histograms of the complex spike (CS) and the simple spike (SS) responses of a representative Purkinje cell in the horizontal zone of the rabbit flocculus to sinusoidal rotation at 0.05 Hz in the light. Note the reciprocity of the CS and SS firing (adapted from  Figure  2 of [80] with permission). (c) Behavior of head velocity plus eye position sensitivity (HVplusP-P cell) recorded in the horizontal zone of the cat (adapted from Figure  3 of [24] with permission). (d) Time course of VOR adaptation corresponding to an out-of-phase VOR-OKN stimulation in 5 cats before (closed circles) and after (open circles) brainstem commissural incision. (e) Example of the VOR adaptation procedure used for increasing the VOR gain. Before the adaptation, the VOR is measured in the dark during table rotation (ℎ) of 40°peak-to-peak at 0.10 Hz; the position of the eye (𝑒) is recorded by means of the search coil technique. The VOR gain is the ratio between the peak-to-peak of the slow phase of the eye velocity and the peak-to-peak of the head velocity. During the training a random pattern of light circles was projected on the drum (d) surrounding the cat and oscillated out of phase of the head rotation, inducing an increase in the amplitude of the eye movements. After 4 hours of such training, the VOR was recorded in the dark and the VOR normalized gain increased by a mean gain of 1.41±0.08 (adapted from Figures  1  and  2 of [77] with permission). Abbreviations: CsC, caudal semicircular canal; Floc, flocculus; Mn, motoneuron; OKN, optokinetic; LR, lateral rectus; VOR, vestibuloocular reflex.