Transient frontopolar cortex stimulation induces prolonged disruption to counterfactual processing.

Frontopolar cortex (FPC) contains area 10, an anterior sub-region of prefrontal cortex exclusive to humans and nonhuman primates (NHPs) which is thought to support monitoring the value of switching between alternative goals. However, the neuronal mechanisms underlying this function are unclear. Here, we used multielectrode arrays to record the local field potentials (LFPs) in the FPC of two macaques performing a Wisconsin Card Sorting Test analogue and found that bursts of gamma and beta in FPC tracked counterfactual not current rule value. Moreover, we show that brief high-frequency microstimulation to a single trial causally affects both LFP activity in FPC, as well as rule-guided decision-making across successive trials. Following stimulation of FPC, we observed reduced exploration of the counterfactual rule prerule-change, as well as a delayed adaptation to the newly relevant rule postrule-change. A similar, multi-trial time-course disturbance to beta and gamma activity within FPC was also induced following single-trial microstimulation. These findings link neuronal activity in FPC with behavioral monitoring of the value of counterfactual rules and provide neural mechanistic insights into how FPC supports rule-based decision-making.