Escitalopram restores reversal learning impairments in rats with lesions of orbital frontal cortex

The term ‘cognitive structures’ is used to describe the fact that mental models underlie thinking, reasoning and representing. Cognitive structures generally improve the efficiency of information processing by providing a situational framework within which there are parameters governing the nature and timing of information and appropriate responses can be anticipated. Unanticipated events that violate the parameters of the cognitive structure require the cognitive model to be updated, but this comes at an efficiency cost. In reversal learning a response that had been reinforced is no longer reinforced, while an alternative is now reinforced, having previously not been (A+/B− becomes A−/B+). Unanticipated changes of contingencies require that cognitive structures are updated. In this study, we examined the effect of lesions of the orbital frontal cortex (OFC) and the effects of the selective serotonin reuptake inhibitor (SSRI), escitalopram, on discrimination and reversal learning. Escitalopram was without effect in intact rats. Rats with OFC lesions had selective impairment of reversal learning, which was ameliorated by escitalopram. We conclude that reversal learning in OFC-lesioned rats is an easily administered and sensitive test that can detect effects of serotonergic modulation on cognitive structures that are involved in behavioural flexibility.