Neuronal activity related to head and eye movements in cat superior colliculus.

1. Movement-related discharges were recorded from single cells in the superior colliculus of alert cats while they made eye saccades (with head fixed) or gaze saccades (with head free). 2. Visual and auditory stimuli were used as saccade targets. In addition, saccades were made to the remembered location of targets and spontaneously, in the absence of targets, during intertrial intervals. 3. When the head was still and the cat performed either spontaneous saccades or saccades to remembered targets, only one class of tectal neurone, the saccade-related burst neurone, inevitably discharged prior to all saccades of appropriate amplitude and direction. 4. Neurones with longer lead times and less intense presaccadic discharges were obligately linked only to visually elicited saccades. The discharge of some of these long-lead neurones was also influenced by the spatial position of the visual target (that is, by craniotopic motor error), while that of the saccade-related burst neurones was a function of retinocentric motor error. 5. Most neurones which discharged before head movements also discharged before eye movements and had large, contralateral movement fields.