Human Insula Activation Reflects Risk Prediction Errors As Well As Risk

TLDR

Reinforcement learning models and primate physiology have shown that the brain encodes reward prediction errors, yet how it predicts and updates risk associated with rewards remains unknown. The authors used fMRI during a gambling task with continuously changing risk to demonstrate that early insula activation correlates with risk prediction error, indicating rapid updating. The results reveal that early insula activation tracks risk prediction error while delayed activation linked to general uncertainty suggests that the neural basis of reward anticipation under uncertainty must include risk prediction.

Abstract

Understanding how organisms deal with probabilistic stimulus-reward associations has been advanced by a convergence between reinforcement learning models and primate physiology, which demonstrated that the brain encodes a reward prediction error signal. However, organisms must also predict the level of risk associated with reward forecasts, monitor the errors in those risk predictions, and update these in light of new information. Risk prediction serves a dual purpose: (1) to guide choice in risk-sensitive organisms and (2) to modulate learning of uncertain rewards. To date, it is not known whether or how the brain accomplishes risk prediction. Using functional imaging during a simple gambling task in which we constantly changed risk, we show that an early-onset activation in the human insula correlates significantly with risk prediction error and that its time course is consistent with a role in rapid updating. Additionally, we show that activation previously associated with general uncertainty emerges with a delay consistent with a role in risk prediction. The activations correlating with risk prediction and risk prediction errors are the analogy for risk of activations correlating with reward prediction and reward prediction errors for reward expectation. As such, our findings indicate that our understanding of the neural basis of reward anticipation under uncertainty needs to be expanded to include risk prediction.