Relationship of simultaneously recorded cerebellar nuclear neuron discharge to the acquisition of a complex,operantly conditioned forelimb movement in cats

This study was designed to examine the changes in the modulation of small populations of cerebellar neurons during the acquisition of a complex, operantly conditioned forelimb task in cats. The experiments are based on the general postulate that, during the learning of a complex motor behavior, the cerebellum is important for generating a coordinated movement that meets the task's objectives, and that, as the cerebellum participates in this process, it acts to reinforce the effective motor pattern once it has been established. This specific study examines whether the changes in the modulation of cerebellar nuclear neurons during the learning of this task are consistent with this view. Cats were required to learn to move the manipulandum through a novel pattern of 2–3 consecutive straight grooves connected end to end in different spatial configurations, e.g., the letter L, an inverted L, and the letter C. Throughout the acquisition process, 6–12 single units were recorded simultaneously in the cerebellar nuclei, and the kinematics of the movement were evaluated using an Optotrak system. Cells were recorded from the two interposed nuclei and the dentate nucleus in these initial studies. Trials were sorted off-line based on the level of skill at which the required movement was performed. This was assessed using several objective criteria such as movement times, kinematic characteristics, and smoothness (number of peaks in the velocity profile). Event-related histograms then were constructed from each group of sorted trials. Changes in modulation related to a specific event were measured in successive histograms for each neuron. One of the most consistent findings across the cells in all nuclei was that the magnitude of the task-related modulation reached a peak at the time the task was first performed reasonably well and then progressively decreased (but did not disappear) as the task became well practiced. Both the initial increase and the subsequent decrease in response amplitude were significant statistically. The implications of these observations are discussed in the context of the role the cerebellum may play in the acquisition of complex motor tasks.