Studies of the role of the paramedian pontine reticular formation in the control of head restrained and head-unrestrained gaze shifts

Results of three experiments related to the role of the paramedian pontine reticular formation (PPRF) in the control of gaze are described. (1) Chronic unit recording methods, used to study the on-directions of short-lead burst neurons In head-restrained monkeys, and (2) reversible inactivation techniques confirmed the traditional view of the importance of PPRF in the control of horizontal eye movements. Reversible inactivation of neurons in the vicinity of identified short-lead burst neurons produced dramatic reductions in the speed of saccades to horizontal target displacements. The reductions in velocity were largely compensated for by an increase in saccade duration. Only minor, if any, effects were observed upon the velocity, duration, and amplitude of saccades to upward target displacements. (3) Microstimulation was applied to omnipause neurons to gate activity of excitatory burst neurons that discharge during coordinated eye-head movements. The microstimulation failed to noticeably slow (prevent) head movements when stimulation was applied during (prior to onset of) gaze shifts, suggesting that signals relayed to motoneurons innervating the neck muscles are not inhibited by the omnipause neurons. In other words, the desired gaze signal is parsed into eye and head pathways upstream of the excitatory burst neurons.