PMID- 12364502
OWN - NLM
STAT- MEDLINE
DCOM- 20021125
LR  - 20171213
IS  - 0022-3077 (Print)
IS  - 0022-3077 (Linking)
VI  - 88
IP  - 4
DP  - 2002 Oct
TI  - In multiple-step gaze shifts: omnipause (OPNs) and collicular fixation neurons 
      encode gaze position error; OPNs gate saccades.
PG  - 1726-42
AB  - The superior colliculus (SC), via its projections to the pons, is a critical 
      structure for driving rapid orienting movements of the visual axis, called gaze 
      saccades, composed of coordinated eye-head movements. The SC contains a motor map 
      that encodes small saccade vectors rostrally and large ones caudally. A zone in 
      the rostral pole may have a different function. It contains superior colliculus 
      fixation neurons (SCFNs) with probable projections to omnipause neurons (OPNs) of 
      the pons. SCFNs and OPNs discharge tonically during visual fixation and pause 
      during single-step gaze saccades. The OPN tonic discharge inhibits saccades and 
      its cessation (pause) permits saccade generation. We have proposed that SCFNs 
      control the OPN discharge. We compared the discharges of SCFNs and OPNs recorded 
      while cats oriented horizontally, to the left and right, in the dark to a 
      remembered target. Cats used multiple-step gaze shifts composed of a series of 
      small gaze saccades, of variable amplitude and number, separated by periods of 
      variable duration (plateaus) in which gaze was immobile or moving at low velocity 
      (<25 degrees /s). Just after contralaterally (ipsilaterally) presented targets, 
      the firing frequency of SCFNs decreased to almost zero (remained constant at 
      background). As multiple-step gaze shifts progressed in either direction in the 
      dark, these activity levels prevailed until the distance between gaze and target 
      [gaze position error (GPE)] reached approximately 16 degrees. At this point, 
      firing frequency gradually increased, without saccade-related pauses, until a 
      maximum was reached when gaze arrived on target location (GPE = 0 degrees). SCFN 
      firing frequency encoded GPE; activity was not correlated to characteristics or 
      occurrence of gaze saccades. By comparison, after target presentation to left or 
      right, OPN activity remained steady at pretarget background until first gaze 
      saccade onset, during which activity paused. During the first plateau, activity 
      resumed at a level lower than background and continued at this level during 
      subsequent plateaus until GPE approximately 8 degrees was reached. As GPE 
      decreased further, tonic activity during plateaus gradually increased until a 
      maximum (greater than background) was reached when gaze was on goal (GPE = 0 
      degrees). OPNs, like SCFNs, encoded GPE, but they paused during every gaze 
      saccade, thereby revealing, unlike for SCFNs, strong coupling to motor events. 
      The firing frequency increase in SCFNs as GPE decreased, irrespective of 
      trajectory characteristics, implies these cells get feedback on GPE, which they 
      may communicate to OPNs. We hypothesize that at the end of a gaze-step sequence, 
      impulses from SCFNs onto OPNs may suppress further movements away from the 
      target.
FAU - Bergeron, Andre
AU  - Bergeron A
AD  - Department of Neurology and Neurosurgery, and Montreal Neurological Institute, 
      McGill University, Montreal, Quebec H3A 2B4, Canada.
FAU - Guitton, Daniel
AU  - Guitton D
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - United States
TA  - J Neurophysiol
JT  - Journal of neurophysiology
JID - 0375404
SB  - IM
MH  - Action Potentials/physiology
MH  - Animals
MH  - Cats
MH  - Fixation, Ocular/*physiology
MH  - Functional Laterality/physiology
MH  - Neurons/*physiology
MH  - Photic Stimulation
MH  - Saccades/*physiology
MH  - Superior Colliculi/*cytology/*physiology
EDAT- 2002/10/05 04:00
MHDA- 2002/11/26 04:00
CRDT- 2002/10/05 04:00
PHST- 2002/10/05 04:00 [pubmed]
PHST- 2002/11/26 04:00 [medline]
PHST- 2002/10/05 04:00 [entrez]
AID - 10.1152/jn.2002.88.4.1726 [doi]
PST - ppublish
SO  - J Neurophysiol. 2002 Oct;88(4):1726-42. doi: 10.1152/jn.2002.88.4.1726.