| Summary: | During flexible behaviour, dopamine is thought to carry reward prediction errors (RPEs), which update values and hence modify future behaviour. However, in real-world situations where the statistical relationships in the environment can be learned, continuously adapting values is not always the most efficient way of adapting to change. Moreover, the environment is not always fully observable, and observations may provide only partial information about the current state of the world. In such partial observable structured environments, as is found in many real-world situations, it is not well understood what kind of information dopamine conveys or its causal role in shaping adaptive behaviour. To probe dopamine’s involvement in goal-directed behavioural flexibility in such environments, we measured and manipulated dopamine while mice solved a partially observable structured sequential decision task. In chapter 3 we show that mice solve such a task using state inference. In chapter 4, we recorded calcium activity from dopaminergic cell bodies in the ventral tegmental area and dopamine axonal projections in the ventral and dorsomedial striatum, as well as dopaminergic concentrations in the same striatal regions. Dopamine multiplexed a wide range of information. At different timescales dopamine signalling was consistent with carrying information about choice-specific RPEs, choice-independent reward history and lateralised movement signals. RPE computations were shaped by task structure and the inferred state of the task. Nonetheless, in chapter 5, we show that although dopamine responded strongly to rewards, optogenetically activating or inhibiting dopamine at the time of trial outcome had no effect on subsequent choice. However, in a different task context, we could show that the same stimulation had a substantial effect on animals’ choices. Therefore, we conclude that when inference guides choice, rewards have a dopamine-independent influence on policy through the information they carry about the world’s state.
|
|---|