Repeated prefrontal transcranial direct current stimulation improves behavioral regulation and modulates resting-state EEG microstate dynamics in young adults with problematic smartphone use: a randomized sham-controlled longitudinal study

Problematic smartphone use (PSU) has emerged as an increasingly prevalent digital behavioral addiction among young adults and is associated with impaired executive control, excessive craving, and altered large-scale brain network organization. Although transcranial direct current stimulation (tDCS) has demonstrated therapeutic potential for addictive disorders, its neurophysiological mechanisms in PSU remain insufficiently understood. This study investigated whether repeated prefrontal tDCS improves behavioral outcomes and reorganizes resting-state electroencephalographic (EEG) microstate dynamics in young adults with PSU.

Eighty participants meeting validated criteria for PSU were randomly assigned to receive active (n = 40) or sham (n = 40) tDCS. Active stimulation (2.0 mA, 20 min/session, three sessions/week for 12 weeks) targeted the left dorsolateral prefrontal cortex. Behavioral outcomes included objectively recorded smartphone use, Smartphone Addiction Scale-Short Version scores, ecological momentary assessment craving, and work and social functioning. Resting-state EEG was recorded under eyes-closed and eyes-open conditions before and after intervention. Canonical EEG microstate temporal characteristics were analyzed using mixed repeated-measures analysis with false discovery rate correction.

Compared with sham stimulation, active tDCS significantly reduced objectively measured smartphone use, craving intensity, and functional impairment while improving behavioral regulation. Neurophysiologically, active stimulation selectively reorganized resting-state brain dynamics. During eyes-closed recording, microstate C occurrence decreased whereas microstate D occurrence increased significantly. During eyes-open recording, both the occurrence and coverage of microstate B increased following active stimulation. No significant changes were observed in global explained variance, suggesting that repeated tDCS primarily modified the temporal organization rather than the spatial configuration of resting-state brain activity.

Repeated prefrontal tDCS produced concurrent behavioral improvement and selective reorganization of resting-state EEG microstate dynamics in young adults with PSU. These findings provide preliminary evidence that repeated prefrontal tDCS is associated with concurrent behavioral changes and alterations in resting-state EEG microstate dynamics in young adults with PSU. Further confirmatory studies are needed to determine the clinical and mechanistic significance of these neurophysiological changes.