Figure 4. Modulation of uncertainty prediction difference in vmPFC according to behavioural mode.

(A) Across all trials, a negative uncertainty (i) and positive accuracy (ii) prediction differences covaried with activation in vmPFC. (B) We found a polarity change in the impact uncertainty exerted on predictor selection at a behavioural level; initial trials in longer horizons were more likely to be explorative and directed towards more uncertain predictors while behaviour in later trials was more exploitative and directed away from uncertain predictors, in other words they selected certain predictors (see labels on y-axis). We tested for a neural uncertainty polarity change in vmPFC comparing behavioural modes of exploration and exploitation, respectively, representing a positive and then negative uncertainty prediction difference. (C) Time courses extracted from vmPFC for both chosen and unchosen components of an uncertainty prediction difference signal during exploration (i) and exploitation (ii). VmPFC BOLD activity changed in accordance with the behavioural results; it transitioned from activity positively related to uncertainty prediction difference (positively encoding the uncertainty of the chosen predictor as opposed to the unchosen predictor) during initial choices to activity negatively related to uncertainty prediction difference (negatively encoding the uncertainty of the chosen predictor as opposed to the unchosen predictor) in later trials. All effects were time-locked to the decision phase. (n = 24; error bars are SEM across participants; whole-brain effects family-wise error cluster corrected with z > 2.3 and p < 0.05). (D) The relationship between accuracy and uncertainty prediction differences used for all neural analyses across all trials (left) exploration trials (centre), and exploitation trials (right). Average correlations between accuracy and uncertainty prediction differences across all participants are reported at the bottom of each panel, while panels show variables across time taken from a representative participant for each analysis. Accuracy and uncertainty prediction differences are similarly decorrelated in all other analyses (for details on correlation, see Supplementary Figure 1, 2).