The Journal of Neurophysiology Vol. 80 No. 6 December 1998, pp. 3373-3379
Copyright ©1998 The American Physiological Society

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New Mechanism That Accounts for Position Sensitivity of Saccades Evoked in Response to Stimulation of Superior Colliculus

A. K. Moschovakis^{1, 2}, Y. Dalezios^{1, 2}, J. Petit³, and A. A. Grantyn³

¹ Institute of Applied and Computational Mathematics, Foundation for Research and Technology, Hellas; and ² Department of Basic Sciences, Faculty of Medicine, University of Crete, Crete, Greece; and ³ Laboratoire de Physiologie de la Perception et de l'Action, Centre National de la Recherche Scientifique-College de France, Paris, France

Moschovakis, A. K., Y. Dalezios, J. Petit, and A. A. Grantyn. New mechanism that accounts for position sensitivity of saccades evoked in response to stimulation of superior colliculus. J. Neurophysiol. 80: 3373-3379, 1998. Electrical stimulation of the feline superior colliculus (SC) is known to evoke saccades whose size depends on the site stimulated (the "characteristic vector" of evoked saccades) and the initial position of the eyes. Similar stimuli were recently shown to produce slow drifts that are presumably caused by relatively direct projections of the SC onto extraocular motoneurons. Both slow and fast evoked eye movements are similarly affected by the initial position of the eyes, despite their dissimilar metrics, kinematics, and anatomic substrates. We tested the hypothesis that the position sensitivity of evoked saccades is due to the superposition of largely position-invariant saccades and position-dependent slow drifts. We show that such a mechanism can account for the fact that the position sensitivity of evoked saccades increases together with the size of their characteristic vector. Consistent with it, the position sensitivity of saccades drops considerably when the contribution of slow drifts is minimal as, for example, when there is no overlap between evoked saccades and short-duration trains of high-frequency stimuli.

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