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Functional Significance of Climbing-Fiber Synchrony

A Population Coding and Behavioral Analysis


Address for correspondence: John P. Welsh, Neurological Sciences Institute, Oregon Health and Science University, 505 NW 185th Avenue, Beaverton, OR 97006. Voice: 503-418-2645; fax: 503-418-2501;


Abstract: Population coding and behavioral approaches were taken toward analyzing the functional significance of the climbing-fiber system. Analyses of neuronal interaction using the joint peristimulus time histogram showed that given a low rate of firing, the climbing-fiber system organizes itself to fire synchronously during movement—a feature that bears little or no relationship to the modulation in firing rate during movement or whether olivary neurons respond to a sensory stimulus. Moreover, the climbing-fiber system avoids synchrony during a passive sensory response but actively makes a transition into synchrony as a movement is initiated. Thus, from a functional viewpoint, the active feature of the climbing-fiber system to organize into synchronously firing cell ensembles is uniquely motor. Analyses of behaving rats without an inferior olive revealed that the climbing-fiber system optimizes the timing of skilled movement by reducing reaction time and the interval between repetitive movements by 100 milliseconds. Finally, using classical delay eyeblink conditioning, it was found that the inferior olive is essential for learning about rapid sequences of events but not the same event sequence when given more slowly. It was concluded that the climbing-fiber system exerts its function through synchrony, which provides a 100 ms advantage in movement speed and the ability to learn about events that are rapidly presented in time.