Discharge patterns of neurons in the rostral superior colliculus of cat: activity related to fixation of visual and auditory targets |
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Authors: | C K Peck J A Baro |
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Institution: | (1) School of Optometry, University of Missouri-St. Louis, 8001 Natural Bridge Road, 63121 St. Louis, MO, USA;(2) Present address: NASA Classroom of the Future, Wheeling Jesuit College, 26003 Wheeling, WV, USA |
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Abstract: | Neurons in the rostral superior colliculus (SC) of alert cats exhibit quasi-sustained discharge patterns related to the fixation
of visual targets. Because some SC neurons also respond to auditory stimuli, we investigated whether there is a population
of neurons in the rostral SC which is active in relation to fixation of both auditory and visual targets. We identified cells
which were active with visual fixation and which continued to discharge if the fixation stimulus was briefly extinguished.
The population of neurons exhibited similar discharge characteristics when the fixation stimulus was auditory. Few neurons
were significantly more active during fixation of visual targets than during fixation of auditory targets. Most fixation neurons
showed a diminished discharge rate during spontaneous (self-generated) saccadic eye movements away from a visual fixation
stimulus, regardless of the direction of the saccade. this diminished discharge rate (or pause) typically began, on average,
12.2 ms before saccade onset and the duration of the pause was Ionger than the duration of the saccade. These observations
are consistent with the hypothesis that increased discharge of these neurons is related to active fixation and that reductions
in their activity are important for the generation of saccades. However, the lack of a precise relationship between pause
duration and saccade duration implies that these neurons would be unlikely to project directly to the saccadic burst generator.
The mean interval from the beginning of the pauses of fixation neurons to be beginning of the saccades away from fixation
targets is also shorter than has been found in brainstem omnipause neurons. By analogy with the concept of a receptive field,
agaze position error field depicts the range of gaze position error for which a cell is active. Although fixation neurons appear to encode the magnitude
and direction of the error between visual targets and the visual axis, visual error fields at the end of fixating eye movements
were significantly larger than those at stimulus onset. For auditory stimuli, this difference was not significant. These observations
are compatible with a number of recent experiments indicating that neural signals of eye position are damped or delayed with
respect to current eye position. |
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Keywords: | Orienting response Visual fixation Attentive fixation Optic tectum |
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