Once the second-step state was revealed, ACC represented whether the transition was common or rare (i.e., the interaction of the transition on the current trial with the state of the transition probabilities) (Figure 5A, magenta). There was no representation of the equivalent interaction of the transition on the current trial with the state of the reward probabilities (Figure 5B, magenta). Finally, ACC represented the interaction of the second-step state reached on the current trial with both the transition and reward probabilities, with both representations ramping up after the second-step state was revealed and persisting till after trial outcome (Figures 5A and 5B, yellow). The interaction of second-step state with the transition probabilities corresponds to the action that commonly leads to the second-step state reached, potentially providing a substrate for model-based credit assignment. The interaction of second-step state with the reward probabilities corresponds to the predicted trial outcome (rewarded or not).
