D2 receptors and cognitive flexibility in marmosets: tri-phasic dose–response effects of intra-striatal quinpirole on serial reversal performance

Behavioral training and testing. a Hypothetical dose–response curve for the potential tri-phasic effects of intra-caudate quinpirole on reversal performance. At the high-dose end of the curve, elevation of dopamine is likely to cause non-specific behavioral disruption as well as increased reversal errors. b Experimental timeline. See “Behavioral Training” in “Supplementary Materials and Methods” for detailed descriptions of the training phases. c Within-session discrimination reversals. At the start of each session (“x”), marmosets learned by trial-and-error that responding to one of two presented stimuli was associated with reward delivery, while response on the other stimulus produced negative auditory feedback. The relative position of visual stimuli varied across trials in a pseudorandom fashion, with each individual stimulus presented equally to the left or right of the reward licker across the session. Once criterion in this “baseline discrimination” phase was reached (6/7 correct trials), these stimulus-outcome associations were reversed. Animals were considered to have successfully reversed these contingencies upon achieving the reversal criterion (6/6 correct trials). In the next session (“x？+？1”), the stimulus that had been rewarded on the reversal phase of the preceding session (“x”) remained rewarded in the baseline discrimination phase. Provided reversal criterion was reached in session “x？+？1”, session “x？+？2” would revert to the same initial stimulus-outcome contingencies as session “x”, and so on. Pharmacological manipulations were performed when marmosets were reliably performing daily within-session reversal