Responses of sagittally aligned Purkinje cells during perturbed locomotion: synchronous activation of climbing fiber inputs.

1. These experiments were performed to test the hypothesis that climbing fiber inputs to sagittally aligned Purkinje cells located in a single folium are activated synchronously in response to a perturbation of the step cycle that interrupts the trajectory of the ipsilateral forelimb. 2. The experiments were performed in acutely decerebrate ferrets capable of walking spontaneously on a moving treadmill. A multiple single-unit recording technique was employed utilizing a fixed array of five sagittally oriented electrodes with electrode tips approximately 200 microns apart. 3. The extent to which the climbing fiber inputs to the recorded Purkinje cells were activated synchronously by the perturbation was calculated for individual trials by determining the synchrony index, a measure of the fraction of the cells responding to each perturbation. 4. The data indicate that there was a statistically significant increase in the synchronous activation of climbing fiber inputs at times immediately after the perturbation. No comparable complex spike modulation was found at the same phase of the unperturbed step cycle. 5. The specific combinations of climbing fiber inputs to neighboring Purkinje cells activated by successive perturbations varied from trial to trial. 6. The implications of these observations are discussed in the context of the nature of the inputs encoded by climbing fiber activation and the role of this afferent system in cerebellar cortical information processing.