Cortical Effects of Brief Daily Periods of Unrestricted Vision During Early Monocular Form Deprivation

Abstract

Experiencing daily brief periods of unrestricted vision during early monocular form deprivation prevents or reduces the degree of resulting amblyopia. To gain insight into the neural basis for these "protective" effects, we analyzed the monocular and binocular response properties of individual neurons in the primary visual cortex (V1) of macaque monkeys that received intermittent unrestricted vision. Microelectrode-recording experiments revealed significant decreases in the proportion of units that were dominated by the treated eyes, and the magnitude of this ocular dominance imbalance was correlated with the degree of amblyopia. The sensitivity of V1 neurons to interocular spatial phase disparity was significantly reduced in all treated monkeys compared with normal adults. With unrestricted vision, however, there was a small but significant increase in overall disparity sensitivity. Binocular suppression was prevalent in monkeys with constant form deprivation but significantly reduced by the daily periods of unrestricted vision. If neurons exhibited consistent responses to stimulation of the treated eye, monocular response properties obtained by stimulation of the two eyes were similar. These results suggest that the observed protective effects of brief periods of unrestricted vision are closely associated with the ability of V1 neurons to maintain their functional connections from the deprived eye and that interocular suppression in V1 may play an important role in regulating synaptic plasticity of these monkeys.

Protection against deprivation amblyopia depends on relative not absolute daily binocular exposure

“…This conclusion was supported by the limited set of data from a third cohort that received 12-h daily visual exposure. Remarkable support was also provided by the results of a study on monkeys that employed a 12-h period of total visual exposure each day (Sakai et al, 2006;Wensveen et al, 2006). The monkeys were maintained in a colony room on a 12-h light-dark cycle from approximately 3 to 21 weeks of age during which time they received mixed visual input on a daily basis.…”

Brief daily binocular vision prevents monocular deprivation effects in visual cortex

“…Our finding that the absolute amount of daily binocular experience has a greater bearing on the cortical territory occupied by the two eyes supports the conclusion that a certain minimum of daily normal vision is necessary and sufficient to maintain a normal V1 architecture. Two previous studies that reported a beneficial effect of daily binocular experience employed either a single predominantly binocular exposure paradigm (Olson & Freeman, 1980) or a limited number of exposure paradigms (with a fixed total daily exposure) followed by a 3‐year period of recovery before physiological recording, which further complicated the interpretation of the data (Sakai et al ., 2006).…”

Visual development in primates: Neural mechanisms and critical periods

“…D), is not closely linked to ocular dominance shifts in V1 and that deficits in some monocular receptive field properties may be more predictive of the vision loss (Kiorpes et al, ; Kiorpes and Movshon, ). However, a few other studies have reported that even monocular receptive field properties in V1 are largely normal despite vision loss following early strabismus (Smith et al, ; Sakai et al, ; Bi et al, ). Whatever the case, an ocular dominance imbalance—as hypothesized based on Wiesel and Hubel's early work—does not appear to directly determine the existence or extent of vision loss that results from early abnormal visual experience.…”