Neuroethology of saccadic eye movements in chickens.
Item
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Title
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Neuroethology of saccadic eye movements in chickens.
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Identifier
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AAI9304691
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identifier
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9304691
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Creator
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Letelier Parga, Juan-Carlos.
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Contributor
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Adviser: Josh Wallman
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Biology, Animal Physiology
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Abstract
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This dissertation studies two main aspects concerning saccadic eye oscillations in chickens: (a) their kinematical description and (b) the activity patterns, in awake subjects, of motoneurons innervating the superior oblique muscle.;During fixations it was found that the range of the horizontal, vertical and torsional components of eye position were similar, each having a value of 15{dollar}\sp\circ.{dollar} Furthermore, in contrast to the case in primates, the amount of torsion was found to be independent of the horizontal and vertical components.;Saccadic oscillations in chickens occur at the rate of 1/sec. They are very stereotyped cyclotorsional movements of the eyeball, having a frequency of 28Hz, an amplitude of 10-12{dollar}\sp\circ{dollar} that does not decay exponentially and a mean speed of 600{dollar}\sp\circ/{dollar}sec. The three position components are strictly linked during oscillations: the eye moves intorsionally, upward and temporally or extorsionally, downward and nasally. While the net eye displacements in both eyes are not always yoked, oscillations are strictly yoked: when one eye is in the intorsional phase of an oscillation the other is in the extorsional phase and viceversa. Oscillations are actively produced by a sequence of contractions and relaxations of the two obliques. The contribution to the oscillations of the other four extraocular muscles is less than 5%.;The motor pool innervating the chick's superior oblique contains two functionally distinct classes of motoneurons. One subpopulation (Tonic) fires during fixations with a rate that increases with intorsion and pauses for at least 35 msec at the beginning of each saccade. The second subtype (Phasic) is totally silent for all fixations and fires a sequence of bursts time-locked to the intorsional phase of each oscillation. A similar division is found among the input fibers coming from the medial longitudinal fasciculus into the trochlear nucleus. Mammalian-like extraocular motoneurons with a tonic-phasic pattern of activity were not observed in the trochlear nucleus. This functional segregation among chicken extraocular motoneurons constitutes an exception to the rule of uniform activation found in the majority of vertebrate motor pools. The firing of Phasic motoneurons appears to be optimized for generating the fastest and most energetically efficient eyeball oscillations. The data collected was used to build a model of the avian saccadic machinery in which the neural command controlling oscillations is not used in producing the net saccadic displacement. (Abstract shortened by UMI.).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
