Adaptation and its Limits

Abstract

A fundamental property of the nervous system is its capability to learn, i.e., to modify its responses in such a way that they are most adequate with respect to the stimuli, according to certain criteria. In the case of the oculomotor reflexes concerned with stabilization of gaze the criterion for optimal performance might well be the absence of more than a minimal amount of retinal image slip when the animal moves around. Since compensatory eye movements are controlled by several sensory systems through complex circuits, many parameters have to be correctly set for a reliable performance, just to name a few: (a) the overall system should be in balance, i.e., no systematic drift in one direction should occur, otherwise the animal will have a spontaneous nystagmus; (b) the gain and phase of the VOR should be neither too large nor too small, which could easily be the case since the VOR is a feed-forward system without direct feed-back from the eye movements to the labyrinth;(c) the gain of the OKN should be adequate to complement the VOR; (d) adequate interaction should exist between canal-ocular, mac-ulo-ocular, optokinetic, and cervico-ocular responses.