A NOVEL INTERPRETATION FOR THE COLLICULAR ROLE IN SACCADE GENERATION

Recently, we found evidence that the activity of neurons in the deep l ayers of the monkey superior colliculus (SC) is modulated by initial e ye position (gain fields). In this paper, we propose a quantitative mo del of the motor SC which incorporates these new findings. Inputs to t he motor map represent the desired eye displacement vector (motor erro r), as well as initial eye position. A unit's activity in the motor ma p is described by multiplying a weak linear eye position sensitivity w ith a gaussian tuning to motor error. The motor map projects to severa l sets of output neurons, representing the coordinates of the desired eye displacement vector, the desired eye position in the head, and the three-dimensional ocular rotation axis for saccades in Listing's plan e, respectively. All these signals have been hypothesized in the liter ature to drive the saccade burst generator. We show that these signals can be extracted from the motor map by a linear weighting of the popu lation activity. The saccadic system may employ all coding strategies in parallel to ensure high spatial accuracy in many complex sensorimot or tasks, such as orienting to multimodal stimuli.