Purkinje cell complex and simple spike changes during a voluntary arm movement learning task in the monkey

1. To evaluate the role of the cerebellum during improvement of voluntary motor performance over time, the discharge of 88 Purkinje cells in the intermediate and lateral cerebellum of two primates (Macaca mulatta) was investigated during a motor learning task involving visually guided arm movements. The animals were trained to move a draftsman's style manipulandum over a horizontally placed video screen. The animals were required to move a cursor from the start box to one of four target boxes by movement of the manipulandum. Errors were introduced into the movement by altering the visual feedback loop, changing the gain between the cursor movement and the hand movement. When a novel gain was presented over 100-200 movement trials, the animals adapted the movements to the new gain. The animals used a strategy of scaling the amplitude and velocity of the initial phase of the movement while keeping the time to peak velocity constant. 2. The learning paradigm consisted of an initial control phase with 35-100 trials at the gain of 1.0. The next 100-200 trials, the learning phase, were presented at one of four gains (0.6, 0.75, 1.5, 2.0). Lastly, a testing phase involved 80% of 100 trials at the learned gain and 20% of the trials randomly interspersed at the control gain of 1.0. An additional "distance control" was used in most experiments to control for the movement scaling associated with learning. In this series of movements using a gain of 1.0, the target box was placed at the distance and direction the hand would have to move in the adapted state. Two aspects of the kinematics were the same for the distance control and the movement at the learned gain: movement amplitude and time to peak velocity. There were, however, slight differences in the peak velocity attained. For gains < 1.0, the peak velocity of the learned task was 14-20% lower than the distance controls, and for gains > 1.0, it was 10-18% higher. 3. After implantation of chronic unit recording hardware, Purkinje cell simple and complex spike discharge was recorded extracellularly during the learning task. The cells were located primarily in the ipsilateral intermediate zone or nearby hemisphere of lobules V and VI. Simple and complex spike histograms, as well as averages of the hand displacement and velocity profiles, were calculated for each phase of the paradigm. To determine the time course of any changes, the learning trials were subdivided into three equal phases.(ABSTRACT TRUNCATED AT 400 WORDS)