McMahon Ward, R. | bioRxiv Science

bioRxiv2024

Neural dynamics in the orbitofrontal cortex reveal cognitive strategies

While the orbitofrontal cortex (OFC) is implicated in learning and inferring latent states, the precise computation performed by OFC for state inference is unclear. Here we show that rat OFC updates beliefs about states, and this process is decipherable from OFC dynamics in rats performing state inference, but not alternative strategies. We trained rats to perform a temporal wagering task with hidden reward states. Well-trained rats used state inference when deciding how long to wait for rewards, and OFC inactivations impaired belief updating about states. Electrophysiology and novel population analysis methods identified latent neural factors reflecting inferred states in rats performing inference, but not other strategies. Neural firing rates and latent population factors showed abrupt changes following trials that were informative of state transitions. These results identify a precise computation performed by OFC, and reveal neural signatures of inference.

neuroscience↗

bioRxiv2024

Acetylcholine demixes heterogeneous dopamine signals for learning and moving

Midbrain dopamine neurons promote both reinforcement learning and movement vigour1-12. A major outstanding question is how dopamine-recipient neurons in the striatum parse these heterogeneous signals. Previous work suggests that cholinergic striatal interneurons may play a role, perhaps by gating dopamine-dependent plasticity13-16, but this has not been tested in behaving animals. Here we studied rats performing a decision-making task with reward- and movement-related events at distinct time points. Optical measurement of dopamine and acetylcholine release in the dorsomedial striatum (DMS) revealed distinct dynamics at task events. Reward cues evoked cholinergic pauses with different phase relationships relative to dopamine. When dopamine slightly lagged cholinergic dips, dopamine predicted future behaviour, and DMS firing rates on subsequent trials. In contrast, when dopamine slightly preceded cholinergic dips, there was no observable relationship between dopamine and learning. Finally, when dopamine was coincident with cholinergic bursts, it preceded and predicted the vigour of upcoming contralateral orienting movements. Our findings suggest that the precise phase relationship between dopamine and acetylcholine allows dopamine to be used for either movement or learning depending on instantaneous behavioural context.

neuroscience↗