TEMPORAL RELATIONS OF THE COMPLEX SPIKE ACTIVITY OF PURKINJE-CELL PAIRS IN THE VESTIBULOCEREBELLUM OF RABBITS

Parasagittal zones in the vestibulocerebellum contain Purkinje cells w hose complex spike (CS) activity is modulated in response to rotationa l optokinetic stimulation (OKS) about either the vertical axis (VA) or a horizontal axis (HA) that is approximately perpendicular to the ips ilateral anterior canal. In rabbits, there are two VA zones in both th e ventral nodulus and flocculus, two HA zones in the flocculus, and on e HA zone in the ventral nodulus. We investigated the temporal relatio nship of the CS activity of Purkinje cell pairs in the same or differe nt zones of the vestibulocerebellum in ketamine-anesthetized pigmented rabbits. A synchronous temporal relationship was defined as the tende ncy of the CS of each Purkinje cell to fire within, at most, 2 msec of one another. Generally, neurons in the same zone showed a tendency to exhibit CS synchrony. Of 82 pairs consisting of two Purkinje cells in the same zone (e.g., two nodulus HA cells), 33 were synchronous. In c ontrast, none of 26 pairs consisting of two neurons in functionally di fferent zones (e.g., a VA cell paired with an HA cell), showed CS sync hrony. Pairs consisting of neurons in spatially separated VA zones in the ventral nodulus also showed a tendency to be synchronously related (6/16), as did pairs consisting of a nodulus VA cell and a flocculus VA cell (3/14). The CS synchrony was higher during OKS in the preferre d direction than during spontaneous activity. This is the first demons tration that CS synchrony in the vestibulocerebellum can be manipulate d with a natural sensory stimulus.