Global neural encoding of model-free and inference-based strategies in mice
When a simple model-free strategy does not provide sufficient outcomes, an inference-based strategy estimating a hidden task structure becomes essential for optimizing choices. However, the neural circuitry involved in inference-based strategies is still unclear. We developed a tone frequency discrimination task in head-fixed mice in which the tone category of the current trial depended on the category of the previous trial. When the tone category was repeated every trial, the mice continued to use the default model-free strategy, as well as when tone was randomly presented, to bias the choices. In contrast, the default strategy gradually shifted to an inference-based strategy when the tone category was alternated in each trial. Brain-wide electrophysiological recording during the overtrained phase suggested that the neural activity of the frontal and sensory cortices, hippocampus, and striatum was correlated with the reward expectation of both the model-free and inference-based strategies. These results suggest the global encoding of multiple strategies in the brain.