Jeffrey C. Erlich @jerlich@qoto.org

UCL is consistently ranked as one of the top ten universities in the world (QS World University Rankings 2010-2022) and is No.2 in the UK for research power (Research Excellence Framework 2021).

Reversal learning measures the ability to form flexible associations between choice outcomes with stimuli and actions that precede them. This type of learning is thought to rely on several cortical and subcortical areas, including highly interconnected orbitofrontal cortex (OFC) and basolateral amygdala (BLA), and is often impaired in various neuropsychiatric and substance use disorders. However, unique contributions of these regions to stimulus- and action-based reversal learning have not been systematically compared using a chemogenetic approach and particularly before and after the first reversal that introduces new uncertainty. Here, we examined the roles of ventrolateral OFC (vlOFC) and BLA during reversal learning. Male and female rats were prepared with inhibitory DREADDs targeting projection neurons in these regions and tested on a series of deterministic and probabilistic reversals during which they learned about stimulus identity or side (left or right) associated with different reward probabilities. Using a counterbalanced within-subject design, we inhibited these regions prior to reversal sessions. We assessed initial and pre-post reversal changes in performance to measure learning and adjustments to reversals, respectively. We found that inhibition of vlOFC, but not BLA, eliminated adjustments to stimulus-based reversals. Inhibition of BLA, but not vlOFC, selectively impaired action-based probabilistic reversal learning, leaving deterministic reversal learning intact. vlOFC exhibited a sex-dependent role in early adjustment to action-based reversals, but not in overall learning. These results reveal dissociable roles for BLA and vlOFC in flexible learning and highlight a more crucial role for BLA in learning meaningful changes in the reward environment. Significance Statement Inflexible learning is a feature of several neuropsychiatric disorders. We investigated how the ventrolateral orbitofrontal cortex (vlOFC) and basolateral amygdala (BLA) are involved in learning of stimuli or actions under reinforcement uncertainty. Following chemogenetic inhibition of these regions in both male and females, we measured learning and adjustments to deterministic and probabilistic reversals. For action learning, BLA, but not vlOFC, is needed for probabilistic reversal learning. However, BLA is not necessary for initial probabilistic learning or retention, indicating a critical role for learning of unexpected changes. For stimulus learning, vlOFC, but not BLA, is required for adjustments to reversals, particularly in females. These findings provide insight into the complementary cortico-amygdalar substrates of learning under different forms of uncertainty.