Central mesencephalic reticular formation (cMRF) neurons discharging before and during eye movement

One hundred twenty neurons were recorded in the central mesencephalic reticular formation (cMRF) of four rhesus monkeys, trained to make visually guided and targeted saccadic eye movements. Eye movements were recorded with the head fixed, using electrooculography (EOG) or subconjunctival scleral search coils. Seventy-six percent (92/120) of cells discharged before and during contraversive visually guided or targeted rapid eye movements, and 76% of these (70/92) responded during contraversive spontaneous saccades in the dark. cMRF neurons had large contraversive movement fields and either a high (> 10 spikes/s) or low background level of spontaneous activity in the dark. The optimal movement vectors (i.e., saccades with greatest response) were predominantly horizontal, although many had a vertical component. Cells with optimal movement vectors within plus or minus 25 degree of pure vertical were more rostral in the MRF and were excluded from the analysis. A model of the cMRF and the SC in the control of saccades is presented. The model simulated the physiological evidence for an almost linear decline in discharge of some individual cMRF neurons with radial error (difference between current and desired eye displacement). We propose that the cMRF eye displacement neurons participate in a servo-loop that provides a current horizontal eye displacement signal to the SC. Feedback to the SC via cMRF eye velocity neurons could also be important in the generation of straight trajectories of oblique saccades.