Our findings that ACC represents predictions of future states and surprise signals when those predictions are violated extends previous findings implicating ACC in prediction and surprise (Alexander and Brown, 2011; Heilbronner and Hayden, 2016). ACC neurons represent values (i.e., predictions of future reward) and reward prediction errors (Matsumoto et al., 2007; Seo and Lee, 2007; Kennerley et al., 2011). Additionally, neurons in primate medial prefrontal cortex (mPFC) respond when the animal must switch from a previously anticipated or preferred course of action (Shima et al., 1996; Isoda and Hikosaka, 2007; Seo et al., 2014). This raises the question of whether the surprise signal we see after a rare state transition reflects the state prediction error itself or its consequences for motor action. As we did not inhibit ACC at the time of the state transition, our manipulation data speak only indirectly to this. However, inhibiting ACC from outcome to choice prevented subjects using the previous state transition to inform the choice, suggesting that ACC is involved in learning from state prediction errors to guide subsequent decisions.
