Albert F. Fuchs

fuchs@u.washington.edu
Professor, Department of Physiology & Biophysics, Core Staff, Regional Primate Research Center

Home Page     Community of Science     Contact Info

Not taking students

Eye movements are elicited by a variety of sensory stimuli, such as the appearance of interesting stationary or moving objects, movements of the head, and movements of the whole visual scene as occur when looking out of a moving vehicle. By using a variety of neurobiological approaches, we have begun to understand how a sensory stimulus elicits an appropriate eye movement response. To illustrate our approach to studying motor behavior, we describe a project concerning the saccadic eye movement, which serves to shift the direction of gaze rapidly from one object to another as in reading or examining a stationary visual scene. Saccades are so rapid that they are over before visual feedback can help guide them to the target. Nevertheless, they are quite accurate. Therefore, the neural command that drives the eye muscles must be programmed very precisely in advance. Amazingly, saccades remain accurate throughout life despite the natural attrition of nerve cells.

Several of our findings suggest that the cerebellum is part of a neural repair shop that keeps the efficacy or gain (Eye amplitude/Target amplitude) of saccades essentially at one. First of all, some cerebellar output cells discharge a burst of spikes for saccadic eye movements, which we elicit in monkeys by rewarding them for following a jumping spot. Second, these cerebellar burst neurons project to cells that synapse directly upon eye movement motoneurons. Third, we can trick the saccadic system into mobilizing the repair shop by causing the target spot to jump backwards as a saccade is made toward it. This behavioral paradigm produces a gradual reduction in saccadic gain (see figure) so that after about 1000 adapting trials, the saccade falls short of the jumping target. If we inactivate the saccade cells in the cerebellum pharmacologically, this behavioral reduction of gain does not occur. We currently are capitalizing on this behavioral adaptation to identify the mechanisms by which the brain modifies its motor capabilities and learns new motor tasks.