Correlates of motor planning and postsaccadic fixation in the macaque monkey lateral geniculate nucleus |
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Authors: | D W Royal Gy Sáry J D Schall V A Casagrande |
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Institution: | (1) Center for Molecular Neuroscience, Vanderbilt University, Nashville, TN 37232-2175, USA;(2) Department of Cell and Developmental Biology, Vanderbilt University Medical School, Medical Center North U3218, Nashville, TN 37232-8240, USA;(3) Center for Integrative and Cognitive Neuroscience, Vanderbilt University, Nashville, TN 37232-2175, USA;(4) Department of Psychology, Vanderbilt University, Nashville, TN 37232-2175, USA;(5) Vanderbilt Vision Research Center, Vanderbilt University, Nashville, TN 37232-2175, USA;(6) Department of Ophthalmology and Visual Sciences, Vanderbilt University, Nashville, TN 37232-2175, USA;(7) Department of Physiology, University of Szeged, Szeged, Hungary |
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Abstract: | There is significant controversy regarding the ability of the primate visual system to construct stable percepts from a never-ending
stream of brief fixations and rapid saccadic eye movements. In this study, we examined the timing and occurrence of perisaccadic
modulation of LGN single-unit activity in awake-behaving macaque monkeys while they made spontaneous saccades in the dark
and made visually guided saccades to discrete stimuli located outside the receptive field. Our hypothesis was that the activity of LGN cells is modulated by efference copies of motor plans to
produce saccadic eye movements and that this modulation depends neither on the presence of feedforward visual information
nor on a corollary discharge of signals directing saccadic eye movements. On average, 25% of LGN cells demonstrated significant
perisaccadic modulation. This modulation consisted of a moderate suppression of activity that began more than 100 ms prior
to the initiation of a saccadic eye movement and continued beyond the termination of the saccadic eye movement. This suppression
was followed by a large enhancement of activity after the eyes arrived at the next fixation. Although members of all three
LGN relay cell classes (magnocellular, parvocellular, and koniocellular) demonstrated significant saccade-related suppression
and enhancement of activity, more cells demonstrated postsaccadic enhancement (25%) than perisaccadic suppression (17%). In
no case did the timing of the modulation coincide directly with saccade duration. The degree of modulation observed did not
vary with LGN cell class, LGN receptive field center location, center sign (ON-center or OFF-center), or saccade latency or
velocity. The time course of modulation did, however, vary with saccade size such that suppression was longer for longer saccades.
The fact that activity from a percentage of LGN cells from all cell classes was modulated in relationship to saccadic eye
movements in the absence of direct visual stimulation suggests that this modulation is a general phenomenon not tied to specific
types of visual stimuli. Similarly, because the onset of the modulation preceded eye movements by more than 100 ms, it is
likely that this modulation reflects higher order motor-planning rather than a corollary of mechanisms in direct control of
eye movements themselves. Finally, the fact that the largest modulation is a postsaccadic enhancement of activity may suggest
that perisaccadic modulations are designed more for the facilitation of visual information processing once the eyes land at
a new location than for filtering unwanted visual stimuli. |
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Keywords: | Primates Vision Thalamus Eye movement Saccade |
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