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Relationship between interocular suppression in V1 and V2 and amblyopia in strabismic monkeys



Conference Title

Society of Neuroscience Annual Meeting


Society of Neuroscience


Chicago, Illinois / October 17-21, 2009

Publication Date / Copyright Date



Recent human psychophysical studies report that amblyopia is linked to robust binocular suppression during early infancy. Previously we have shown that V1 physiology of strabimsic monkeys is dominated by interocular suppression (i.e., binocular responses are weaker than monocular responses) that immediately begins with the onset of strabismus. In this study we determined whether the prevalence of interocular suppression in V1 and V2 neurons of strabismic monkeys with a range of amblyopia is related to behaviorally determined degree of amblyopia in individual monkeys. Infant monkeys were reared with surgical strabismus (esotropia) between 3 weeks and 18 months of age. Since in some monkeys with surgical strabismus, visual axes may return to normal positions sometime after strabismus onset, eye alignment was monitored during early development (first 8-10 months). Between 18 and 24 months of age, our standard operant methods were used to obtain the spatial contrast sensitivity function for the deviating and fellow eye in each monkey from which the severity of amblyopia was determined by calculating amblyopia index for the monkey. Binocular responses of V1 and V2 neurons were analyzed using our standard microelectrode recording and analysis methods in anesthetized monkeys. High contrast sinusoidal gratings were dichoptically presented and the relative spatial phase was varied between the two eyes. We compared the peak firing rate of each unit under dichopitc stimulation to dominant monocular response rate. We found that our strabismic monkeys (n=9) exhibited a wide range of amblyopia (i.e., amblyopia index ranged between 0.3 and 0.9). Longer duration of misalignment generally resulted in a larger amblyopia index value. Binocular interactions in V1 and V2 were dominated by interocular suppression and the prevalence of suppressive units (i.e., peak binocular/monocular rate < 0 db) in individual monkeys varied with their amblyopia index values. The proportion of binocular suppressive units in V1 and V2 of each monkey was highly correlated with its amblyopia index; i.e., the greater the degree of amblyopia, the higher the prevalence of binocularly suppressive neurons in V1 and V2. Although our findings appear to be consistent with the results of psychophysical studies in humans, the exact nature of this relationship is yet to be determined.



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