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The present study examined the effects of the presence of a competitoron the behavior of individual rats in a foraging paradigm as was done in Farmer-Dougan, Dougan, Knight, Toelle, and Chandrashekar (2007). Rats foraged for food in a large open field, with pellets delivered in one patch on a Variable Interval schedule (VI). During alone conditions, each rat foraged by itself. During the unpredictable competitor condition, a competitor rat was introduced on an unpredictable basis on the last day of foraging. In this condition, the rats displayed avoidance behavior and were significantly undermatching as was observed in Farmer-Dougan et al. (2007). During the predictable competitor condition, the competitor rat was always present. These rats were significantly overmatching and engaged in a competitive wrestling behavior that was casually observed in Farmer-Dougan et al. (2007). The behavioral topographies were coded after behavioral testing was complete to examine the occurrence of avoidance behaviors and competitive wrestling behaviors in each condition. After the last session of foraging, the rats were sacrificed and c-Fos analysis was completed on the amygdala and nucleus accumbens. The results showed that the rats engaged in the expected behavioral responses with rats in the predictable competitor condition ofspending more time at the feeder, and they also had higher c-Fos expression in the nucleus accumbens. Rats in the unpredictable competitor condition spent more time away from the feeder, more time grooming, and more time engaging in other social avoidance behaviors; they also had significantly higher levels of c-Fos expression in the amygdala. The present data expand the literature comparing the matching law to the idea free distribution by examining the differences in behavioral responses and the neural correlates.



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