Medial Frontal Theta Reduction Impairs Rule Switching via Prediction Error

Cognitive flexibility, the ability to switch behavior in response to changing rules in an uncertain environment, is crucial for adaptive decision-making. Prior research has hypothesized a key role of prediction error and theta oscillations in the medial frontal cortex in this process. However, the causal link between such processes remains to be established. To address this, we combined neural stimulation, EEG, behavioral measurement, and computational modeling. Specifically, we applied high-definition transcranial direct current stimulation to modulate theta oscillations as measured via EEG followed by a probabilistic reversal learning task in 48 adults (18 female and 30 male human subjects). We found that anodal stimulation reduced theta power and rule prediction error, and it increased the number of trials needed to reliably switch between rules. These findings support the role of rule prediction error signaling as a key mechanism linking neural oscillations to behavioral adaptation and highlight the importance of theta power and rule prediction error for cognitive flexibility.