Some collicular efferent neurons code saccadic eye velocity.

The activity of identified tecto-reticulo-spinal neurons (TRSNs) was studied in alert head-fixed cats during orienting towards moving visual stimuli. Eye movements and dorsal neck muscle activity were recorded simultaneously. Burst parameters of TRSNs showing visuomotor properties were analysed quantitatively. It could be demonstrated that some neurons generate presaccadic bursts whose instantaneous frequency profile is closely correlated with the profile of saccadic eye velocity. This correlation could be revealed only under conditions in which cats made orienting saccades to 'catch' a target moving in the preferred direction of the neuron's visual receptive field. Latency between bursts and saccades varied depending upon the degree of attention toward the target and saccade direction.