Beta-Band Stimulation of Dorsolateral Prefrontal Cortex Through tACS Alters Mental Time Travel and Prospective Memory, but Not Delay Discounting

Abstract

Highlights What are the main findings? Beta-tACS over bilateral DLPFC selectively improves mental time travel accuracy for past and present reference points, leaving future projections unaffected. Beta-tACS increases delay discounting steepness and enhances time-based prospective memory precision, without altering clock-checking behavior. What are the implications of the main findings? DLPFC beta oscillations support the maintenance of concrete, temporally proximal representations rather than a unitary future-cognition mechanism. Abstract Background: Future-oriented cognition involves several neurocognitive processes putatively supported by the dorsolateral prefrontal cortex (DLPFC) and beta-band oscillations. This study aimed to corroborate the role of beta oscillations in the DLPFC during three future cognition tasks: mental time travel (MTT), delay discounting (DD), and time-based prospective memory (PM). Methods: Thirty-three participants (22–29 years) completed the three tasks under two conditions—active and sham stimulation—administered in a counterbalanced within-subjects design, one week apart. Beta-frequency transcranial alternating current stimulation (tACS; 22 Hz, 1.5 mA) was applied bilaterally over the DLPFC (F3–F4). Results: Beta-tACS was associated with dissociable effects across domains. In MTT, stimulation selectively improved accuracy for ordinality judgements anchored to past and present reference points (2014, 2024), without affecting future projections (2034) or reaction times. In DD, beta-tACS did not modify the steepness of temporal discounting in a statistically significant way. In PM, stimulation enhanced both dichotomous accuracy and continuous temporal precision, with no changes in clock-checking behavior. Conclusions: These findings provide preliminary evidence that suggests a possible role of DLPFC beta oscillations in supporting the maintenance and utilization of more concrete temporal representations across distinct temporal domains, resulting in anchoring in more available representations (MTT) and focus on temporal information (PM), challenging unitary accounts of prefrontal beta function and highlighting task-dependent neuromodulation effects within the future temporal domain.