Gaze shift duration, independent of amplitude, influences the number of spikes in the burst for medium-lead burst neurons in pontine reticular formation

Abstract

Changes in the direction of the line of sight (gaze) allow successive sampling of the visual environment. Saccadic eye movements accomplish this goal when the head does not move. Medium-lead burst neurons (MLBs) in the paramedian pontine reticular formation (PPRF) discharge a high frequency burst of action potentials starting ~12 ms before the saccade begins. A subgroup of MLBs rostral of abducens nucleus monosynaptically excites oculomotor neurons. The number of spikes in the presaccadic burst is correlated with the amplitude of the horizontal component of the saccade, and the peak discharge rate is correlated with peak eye velocity. During head-unrestrained gaze shifts, a linear relationship between the number of action potentials in MLB bursts and gaze (but not eye) amplitude has been reported. The anatomical connection of MLBs to motor neurons and the similarity between the phasic motor neuron burst and MLB discharge have raised questions about the usefulness of counting spikes in MLBs to determine their role in eye-head coordination. We investigated this issue using a behavioral technique that permits a dissociation of eye movement amplitude and duration during constant vector gaze shifts. Surprisingly, during gaze shifts of constant amplitude and direction, we observe a nearly linear, positive correlation between saccade duration and spike number associated with a negative correlation between spike number and saccade amplitude. These data constrain models of the oculomotor controller and may further define the time-dependence of hypothesized neural integration in this system.

Dynamic control of eye-head gaze shifts by a spiking neural network model of the superior colliculus

“…Animals received a small liquid reward for each successful trial. Details on surgical procedures, training protocols, and experimental setup are described in full detail elsewhere ( Quessy and Freedman, 2004 ; Quessy et al, 2010 ; Walton and Freedman, 2011 ). Additional details on the experimental paradigm are provided in the Supplementary material .…”

Maps and sensorimotor transformations for eye-head gaze shifts: Role of the midbrain superior colliculus

“…Animals were trained to follow briefly flashed visual targets against a small liquid reward by generating rapid eye-head gaze shifts, while single-unit activity from the left SC was recorded. Details on the surgical procedures, training protocols, and experimental setup are described in full detail in Quessy and Freedman (2004), Quessy et al (2010), and Walton and Freedman (2011). All experimental procedures were approved by the University of Rochester Animal Care and Use Committee, and fully adhered to the National Institutes of Health Guide for the Care and Use of Animals.…”

Stimulation of Pontine Reticular Formation in Monkeys With Strabismus

“…18,19 The MLBs directly activate motoneurons, providing an instantaneous horizontal saccadic velocity command. [20][21][22] This signal also is passed through the horizontal neural integrator in nucleus prepositus hypoglossi to provide the tonic component of motoneuron discharge. Stimulation of PPRF in normal monkeys evokes constant velocity, ramp-like, ipsiversive eye movements that persist as long as the train continues.…”