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Bilateral orbital prefrontal cortex lesions disrupt reinforcer devaluation effects in rhesus monkeys

, : Bilateral orbital prefrontal cortex lesions disrupt reinforcer devaluation effects in rhesus monkeys. Society for Neuroscience Abstracts 26(1-2): Abstract No -366 1

The orbital prefrontal cortex (PFo) appears to operate as part of a network involved in reward-based learning and goal-directed behavior. To test whether PFo is necessary for guiding behavior based on expected reward outcomes, we compared 4 rhesus monkeys with two-stage bilateral PFo removals and 6 unoperated controls for their responses to reinforcer devaluation. Surgeries were performed by aspiration in two stages (left PFo removal followed by right, n=2; right PFo removal followed by left, n=2). After the unilateral surgery or rest, monkeys learned 60 object discrimination problems. Half of the positive objects were baited with one type of food, and the other half with a different food. To assess the effects of reinforcer devaluation, we administered critical trials in which monkeys made choices between pairs of positive objects, each of which had been associated with a different food. There were 4 sessions of critical trials, 2 preceded by a selective satiation procedure intended to devalue one of the two foods, and 2 preceded by no satiation (baseline sessions). Monkeys with unilateral PFo removal and controls did not differ in trials to criterion during initial learning. Monkeys with unilateral PFo lesions also did not differ from the controls on our test of reinforcer devaluation; both groups tended to avoid choosing objects associated with the devalued food. After the second stage of surgery or rest, monkeys relearned the same set of 60 object pairs. Although the groups did not differ in relearning, monkeys with bilateral PFo removals showed an attenuation of reinforcer devaluation effects, whereas controls continued to show robust devaluation effects (F(1,8) = 6.03; p<.05). Tests carried out before and after the second-stage surgery indicate that preferences among a group of 6 foods remain largely unchanged in the operated subjects. The findings are consistent with the idea that PFo is critical for adaptive response selection.


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