Role of cat pontine burst neurons in generation of saccadic eye movements.

Abstract

The activity of putative excitatory premotor neurons in the brain stem of the alert, trained cat was recorded to provide information on the anatomical and electrophysiological circuitry involved in the generation of saccadic eye movements. Extracellular responses were recorded from neurons that discharged a high-frequency burst of action potentials immediately before and during saccadic eye movements and fast phases of optokinetic nystagmus but not smooth eye movements. Each burst neuron (BN) discharged most vigorously for saccades in a particular direction, termed the on-direction. Saccades in the on-direction were associated with the highest average frequencies, the greatest number of action potentials, and the longest latencies from burst onset to saccade onset. The on-direction for every horizontal BN was ipsilateral, although some BN discharged less vigorously for saccades over a wide range of directions. Extensive quantitative correlations were performed between the various parameters performed between the various parameters describing the saccadic eye movements and the parameters describing the burst discharge for a number of different populations of saccades. The best correlation was between the number of action potentials in the burst and the size of the saccade. The duration of the burst was not well corellated with the duration of the saccade. BN were located rostral and ventral to the abducens nucleus. These BN represent the direct excitatory premotor neurons responsible for the generation of saccades. These BN are probably premotor neurons whose discharge patterns have sufficient information to create saccadic eye movements; they determine the amplitude of the saccade by the number of action potentials within the burst and they determine saccade direction by their on directions (i.e.. which neuron is firing).