Transcranial alternating current stimulation over left DLPFC modulates feedback processing: a simultaneous tACS-fMRI study

Studies have shown that reward-related feedback is processed by distinct brain networks. Neuronal oscillations, particularly theta and beta rhythms, play a key role in facilitating communications within these networks. This study investigated how modulating brain oscillations at theta and beta frequencies using transcranial alternating current stimulation (tACS) influences activation in brain regions involved in feedback processing. In three separate sessions, 28 healthy participants received either theta (5 Hz), beta (25 Hz), or sham tACS over the left dorsolateral prefrontal cortex (DLPFC) while performing a gambling task. fMRI data were recorded simultaneously with tACS to measure BOLD activations associated with gain and loss feedback. Results showed that theta stimulation enhanced activity in brain regions related to sensory processing, error monitoring, cognitive control, and emotion regulation during loss feedback. On the other hand, beta stimulation modulated activation in areas associated with reward sensitivity and emotional processing during gain feedback. These findings demonstrate the distinct roles of theta and beta oscillations in negative and positive feedback processing.