Sunday, January 7, 2007

Impact of Experience on the Representation of Object-Centered Space in the Macaque Supplementary Eye Field.

Many neurons in the macaque supplementary eye field (SEF) exhibit object-centered spatial selectivity, firing at different rates when the monkey plans a saccade to the left or right end of a horizontal bar. Is this property natural to the supplementary eye field or is it a product of specialized training in the laboratory? To answer this question, we monitored the activity of single SEF neurons in two monkeys before and after training to select eye-movement targets by an object-centered rule. During stage 1, the monkeys performed a color delayed-match-to-sample (DMS) task in which a red or green central cue dictated an eye movement to the matching end of a horizontal bar. Many neurons at this stage exhibited object-centered spatial selectivity. During stage 2, the monkeys performed a color-conditional object-centered task in which a green or red central cue instructed an eye movement to the left or right end of a gray bar. More neurons exhibited object-centered spatial selectivity during this stage than during stage 1. During stage 3, the monkeys again performed the color DMS task. The fraction of neurons exhibiting object-centered spatial selectivity remained at a level comparable to that observed during stage 2 and above that observed during stage 1. Thus object-centered spatial selectivity was present before training on an object-centered rule, was enhanced as a product of object-centered training, and outlasted active use of an object-centered rule. We conclude that neural representations of object-centered space, naturally present in the primate brain, can be sharpened by training.

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