Neural Representation of Saccadic Eye Movements in Monkey Superior Colliculus

Just prior to and during a saccadic eye movement a large population of neurons in the midbrain superior colliculus (SC) is recruited, representing a desired vectorial eye displacement in a topographically organized motor map. The SC transmits its output to horizontal and vertical burst cells in the brainstem, which generate the appropriate high-velocity commands for the oculomotor plant. Substantial experimental evidence suggests that saccade generation is under continuous feedback control. An important problem for models of the saccadic system is, how the spatial representation of the SC output is transformed into the temporal code of brainstem cell populations. This problem is even more intriguing, when the possibility is considered of a dynamic feedback loop which includes the SC. Recent experimental findings support such a possibility. In this paper we describe the properties of a two-dimensional neural network model for the monkey SC, which incorporates a number of realistic features known from neurophysiology and, in addition, is inside the dynamic feedback loop for saccade generation. We show that, in order to generate goal-directed saccades, both the feedforward and feedback synaptic connections of the SC neurons should be organized topographically. Several interesting emerging properties of the model are discussed.