College of Optometry Faculty Proceedings, Presentations, Posters, Speeches, Lectures, etc.

Title

High prevalence of interocular suppression in macaque V1 after only 3 days of early strabismus

Format

Poster

Conference Title

Society of Neuroscience Annual Meeting

Organization/Association/Group

Society of Neuroscience

Location

New Orleans, Louisiana / November 8-12, 2003

Publication Date / Copyright Date

11-9-2003

Abstract

Experiencing interocularly conflicting signals early in life results in a higher than normal prevalence of V1 neurons that exhibit binocular suppression. The increase in binocular suppression occurs presumably because the fine balance between excitatory and inhibitory inputs that exist in normal V1 neurons is lost over time in favor of suppressive influences. How interocular suppression becomes the dominant residual binocular interactions in V1 of strabsimic subjects is not well understood. One of the major hypotheses is that increased suppression reflects changes in the relative density of excitatory vs. inhibitory synaptic boutons in the local and/or long-range intrinsic connections in favor of inhibitory connections. We tested this idea by determining whether exceedingly brief periods (3 days) of early strabismus, which are highly unlikely to induce extensive sprouting or retraction in the local and/or long-range intrinsic connections, lead to a high prevalence of suppression. Our microelectrode experiments in anesthetized and paralyzed infant monkeys demonstrated that after 3 days of optical strabismus beginning at 4 weeks of age, the prevalence and magnitude of interocular suppression in V1 greatly increased while the sensitivity of these units to interocular spatial phase disparity was virtually unaffected. This result was in part due to a higher than normal proportion of disparity-sensitive units that also exhibited interocular suppression. Interestingly, longer durations of strabismus (e.g., weeks or months) did not influence the prevalence of binocular suppression. These results suggest that the cortical mechanisms underlying interocular suppression in strabismic monkeys do not necessarily require wholesale changes in the synaptic structure of the intrinsic connections in V1.

Disciplines

Optometry

Keywords

visual cortex, binocular, monkey

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