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Eye Movement Related Single-Unit Recording In The Nucleus Reticularis Tegmenti Pontis In The Alert Monkey

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Dissertation - Pacific Access Restricted


Nucleus Reticularis Tegmenti Pontis (NRTP) is a structure which lies in the mid-brain ventral to the oculomotor complex. Anatomical studies strongly implicate it in oculomotor function as most of its inputs and outputs are to systems previously shown to be intimately involved in eye movement generation--superior colliculus (SC) and cerebellum. These reports show an integrative structure with inputs and outputs distributed in a way well suited for performing relay and feedback tasks. Physiological data in the alert, trained monkey has been gathered in an attempt to characterize these neurons and to classify them in functional terms. Three monkeys were trained to perform tasks related to rapid (saccadic) or slow (pursuit) eye movement production. Units were initially divided into two groups; those active only in association with saccades (Pure Burst units) and those remaining active during the intersaccadic interval (Spontaneously Active units). This latter category was further subdivided on the basis of the regularity of intersaccadic discharge, excitation or inhibition during saccades, modulation during pursuit tracking, modulation by fixation position, and visual sensitivity. Of the 70 units judged to lie within or close to the NRTP, 35 of these were Pure Burst units. Fifty-eight percent of the Pure Burst units had a maximum of activity associated with saccades made to a particular location in the saccadic field--the movement field (MF). Some of these also had a sensitivity to the visual reward target. In these respects, the NRTP shares similarities with units within the intermediate layers of the superior colliculus--one of its major inputs. Of the 25 Spontaneously Active units, Burst/Spontaneous units (12) possessed an uneven ongoing discharge rate during intersaccadic fixation which was, for most units, insensitive to fixation position. These units either burst in one direction and paused in the other or displayed a burst-pause sequence in one direction and were unmodulated for saccades in the opposite direction. Forty-three percent of the Burst/Spontaneous units had a movement field. Burst/Spontaneous Pursuit units (3) discharged unevenly during fixation, burst for saccades in certain directions, and were modulated during smooth pursuit. Burst/"Tonic" units (4) discharged at high and regular rates during fixation and burst-paused for saccades in certain directions. The tonic discharge of two of these units was sensitive to fixation position. Pause units (6) paused for saccades in most directions, and in some cells had a spontaneous rate which was modulated by fixation position and during certain phases of pursuit tracking. The results show that units found in NRTP share many charactertistics with those structures to which NRTP forms it major connections. The MF units in NRTP are much like those in SC. However, the onset of activity is well outside the range reported for SC. The Pure Burst units appear to lack the strong burst-duration relationship and the Spontaneously Active units appear to lack the strong position dependency found in the cerebellum.

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