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L.C. Osborne and S.G. Lisberger

Sloan Center for Theoretical Neurobiology and Howard Hughes Medical Institute, University of California, San Francisco

Tight correlation between dynamics of smooth pursuit eye movements and adaptation of neural responses in visual area mt in monkeys

MT neurons show an adaptation in which the response to target motion in their preferred direction is attenuated by a prior "conditioning" target motion. In most neurons, the adaptation is direction-dependent and recovers when the interval between the conditioning and testing stimulus is more than 64 ms. Since MT is a major source of visual motion inputs for pursuit eye movements, we tested whether the same adaptation was seen in pursuit. Visual stimuli consisted of random dots within a 5x5 degree window centered 5 degree eccentric along the horizontal axis. Monkeys were trained to fixate a small target at straight-ahead gaze during a conditioning stimulus that consisted of dot motion within the stationary window. Pursuit was then initiated by extinguishing the fixation point and moving the dots and the window together towards the position of fixation. With training, pursuit was as good for moving dots as for stimuli that also contained a clear tracking target. To ensure that we considered only the pursuit driven directly by visual inputs before visual feedback, we analyzed eye acceleration in the first 100 ms of pursuit. We found that the conditioning stimulus had a striking effect on pursuit when the condition-test interval was zero. If the conditioning motion was in the same direction as test motion, pursuit was delayed and peak eye acceleration was lowered, relative to control responses obtained when the conditioning dots were stationary. Conditioning motion in the opposite direction had the least effect and vertical conditioning had intermediate effects. The time course of recovery of the adaptation was assessed by stopping the conditioning dots for different times before the pursuit stimulus was presented. In different monkeys, delays of 64 to 128 ms were required to allow recovery to control values of latency and initial eye acceleration. Experiments using two patches of dots on either side of the fixation spot show that conditioning motion adapts the pursuit response in a spatially specific manner. The directional specificity, spatial specificity, and the time course of the recovery of pursuit adaptation are very similar to the results of similar experiments on cells in MT. (Supported by the Howard Hughes Medical Institute and the Alfred P.\ Sloan Foundation.)


next up previous
Next: Alex Pouget Up: No Title Previous: Mike W. OramMatthew

Tony Zador
Sat Mar 27 10:58:21 PST 1999