Transcranial direct current stimulation above the medial prefrontal cortex facilitates decision-making following periods of low outcome controllability

Recent studies suggest that choice behavior in reinforcement learning tasks is shaped by the level of outcome controllability. In particular, “Pavlovian bias” (PB) seems to be enhanced under low levels of control, manifesting in approach tendencies towards rewards and response inhibition when facing potential losses. PB has also been associated with learned helplessness (LH), raising the possibility that motor passivity and poor coping capabilities in clinical conditions with LH are due to exaggerated PB in decision-making. The medial prefrontal cortex (mPFC) has been implicated both in evaluating outcome controllability and in the development of LH. The current study tested if high-definition transcranial direct current stimulation (HD-tDCS) above the mPFC of healthy humans can influence PB, and counteract the previously documented, deleterious behavioral effects of low outcome controllability during reinforcement learning. In a pre-registered, between-group, double-blind study (N = 103 adults, both sexes), we tested the interaction between controllability and HD-tDCS on parameters of choice behavior in a Go/NoGo task. Relative to sham stimulation, active HD-tDCS resulted in more robust performance improvement following reduced control, an effect that was more pronounced in appetitive trials. In addition, we found evidence for weaker PB when active HD-tDCS was administered during low controllability over outcomes. Computational modeling revealed that parameter estimates of learning rate and choice randomness were modulated by controllability, HD-tDCS and their interaction. Overall, these results highlight the potential of our HD-tDCS protocol for interfering with choice arbitration under low levels of control, resulting in more adaptive behavior.