Lesions of the orbital prefrontal cortex impair the formation of attentional set in rats

In rats, reversal learning impairments are commonly reported after lesions of the orbital prefrontal cortex (OFC), in contrast to the effect of lesions of the medial prefrontal cortex, which impair attentional set-shifting. Comparable dissociations have also been reported in humans, monkeys and mice. However, these two manifestations of behavioural flexibility may share common cognitive processes. The present study tested the hypothesis that lesions of the OFC (an area that integrates expected and actual outcomes to signal which cues in the environment predict reward) would impair the formation of attentional set as well as impairing reversal learning. We compared the performance of lesioned and control rats on two set-shifting tasks. The first task we used, the 4ID task, had no reversal stages, but multiple intradimensional acquisitions before the extradimensional shift stage, to assess set-formation as well as set-shifting. The second task was the standard intradimensional/extradimensional 7-stage task, which includes reversal learning stages after each compound acquisition. Compared with controls, lesioned rats were slower to form attentional set on the 4ID task. When they did form a set, they required more trials to complete the extradimensional shift stage. On the 7-stage task, we replicated our previous finding of impaired reversal learning and reduced shift-costs. We interpret these findings as reflecting a single deficit in identifying relevant cues after unexpected outcomes, which supports recent models of OFC function. Our findings challenge the assumption that the contribution of the OFC to behavioural flexibility is limited to reversal learning.