The role of cerebellum in dopamine neuron reward prediction error coding

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Making and evaluating predictions is a fundamental feature of brain function. All animals learn from experience to optimize their behaviour for survival, yet we don't know how key 'prediction nodes' in the brain talk to each other, or indeed what the conversation is. Consider the familiar jingle of an ice cream van; our brains have learnt through experience that this sound signals the availability of ice cream and how good the treat will be, guiding our decision to approach, or avoid it. The cerebellum and ventral tegmental area (VTA) are critical hubs for prediction, but until now have been considered as independent systems. New evidence reveals prominent connections from the cerebellum to the VTA that can influence reward-seeking behaviour and thus 1) redefine our view of the function of these systems and 2) indicate that predictions may be coordinated throughout the brain. The goal of this proposal is to provide a detailed circuit-level characterisation of the role of the cerebellum in the encoding of reward prediction error in the VTA. To achieve this, we will first map the organisation of cerebellar input onto dopaminergic and non-dopaminergic neurons within the VTA. Second, we will define the nature of the cerebellar signal to the VTA by recording from projection neurons during reward prediction behaviour. Third, we will selectively disrupt these inputs during behaviour to establish how the cerebellum shapes reward prediction error coding in the VTA. This work is essential to develop an integrated understanding of predictive coding and reward processing in the brain. Our findings will further the development of biologically plausible learning algorithms, and identification of targets for the maintenance and restoration of reward processing systems during ageing.