Bilateral parietal tRNS improves processing speed on the paced auditory serial addition test (PASAT): behavioral and ERP evidence

OBJECTIVE: Cognitive control is essential for goal-directed behavior and is often impaired in neurological conditions. Transcranial random noise stimulation (tRNS) has shown potential for cognitive enhancement, but its electrophysiological mechanisms remain unclear. This study examined whether bilateral parietal tRNS modulates paced auditory serial addition test (PASAT) performance (reaction time and accuracy) and event-related potential (ERP) indices of cognitive control. METHODS: In a randomized, double-blind, sham-controlled crossover study, 40 healthy adults received active high-frequency tRNS (100-640 Hz, 2 mA, 20 min) or sham stimulation over bilateral posterior parietal regions. PASAT performance (reaction time, accuracy) and EEG were recorded pre- and post-stimulation. ERP analyses focused on N200, P300, and late slow wave (LSW). RESULTS: Active tRNS significantly reduced reaction times compared to sham, with no stimulation-specific effect on accuracy. Neurophysiologically, active tRNS reduced frontal N200 negativity and increased frontal P300 amplitude. Additionally, reductions in reaction time were significantly associated with increases in frontal P300 amplitude. CONCLUSIONS: The findings suggest that a single session of bilateral parietal tRNS reduced response latency and was associated with changes in frontal ERP markers during a demanding cognitive task. These results provide preliminary electrophysiological evidence that parietal tRNS may influence task-related neural activity expressed at frontal sites, with ERPs serving as potential markers of stimulation-related changes in performance.