A single 20-minute session of high-frequency transcranial random noise stimulation (tRNS) delivered over both sides of the parietal cortex made healthy adults respond faster on one of neuropsychology’s most demanding attention tests, according to a randomized, double-blind, sham-controlled crossover study published in Behavioral and Brain Functions. Forty participants completed the paced auditory serial addition test, or PASAT, before and after receiving either active stimulation or a sham procedure. Reaction times dropped significantly after active tRNS compared with baseline, while accuracy improved to a similar degree in both conditions, meaning the stimulation specifically sped responses rather than making people more correct.
The PASAT is a punishing task by design. Participants hear a stream of single digits from 1 to 9 and must add each new digit to the one presented immediately before it, so every incoming number has to be held in working memory, combined with its predecessor, and answered within a two-second window, all while suppressing interference from earlier sums. Because the task taxes sustained attention, working memory updating, and rapid processing under time pressure, it has long been used to probe cognitive control in both healthy people and clinical groups, particularly those with traumatic brain injury and multiple sclerosis. Neuroimaging work shows that successful PASAT performance recruits a bilateral frontoparietal network including the dorsolateral prefrontal cortex, the anterior cingulate cortex, and the posterior parietal cortex.
The stimulation itself was straightforward but precisely specified. Researchers at Dalian University of Technology placed two saline-soaked sponge electrodes over positions P3 and P4 of the international 10–20 EEG system, targeting bilateral posterior parietal regions. In the active condition, high-frequency tRNS ranging from 100 to 640 Hz was delivered at a 2 mA peak-to-peak amplitude for 20 minutes, producing a maximum current density of roughly 0.029 mA/cm². Electric field modeling in SimNIBS confirmed that the strongest field intensities fell over the bilateral posterior parietal cortex. In the sham condition, current flowed only during the first 60 seconds, with 30-second ramps up and down, to preserve blinding. Participants and the behavioral and EEG recorders were unaware of which condition they were testing, and a blinding questionnaire confirmed that guesses did not differ between conditions.
The study enrolled 40 right-handed university students with normal or corrected-to-normal vision and hearing, no history of neurological or psychiatric disorders, and normal scores on depression and anxiety screening instruments. Each person completed two sessions, one active and one sham, in randomized and counterbalanced order separated by at least three days to minimize carry-over effects. During each session, EEG was recorded continuously while participants performed three blocks of the PASAT before stimulation and three blocks afterward, with different task versions used across blocks to reduce repetition effects. No task was performed during the stimulation period itself.
The behavioral results hinged on an interaction between stimulation condition and time. For reaction time, the repeated-measures analysis of variance showed a significant stimulation-by-time interaction, and post-hoc tests revealed that reaction times were significantly shorter after active tRNS than at baseline, with a corrected p value below 0.001, a 95 percent confidence interval of 20.02 to 71.17 milliseconds, and a Cohen’s d of 0.60. The sham condition showed no significant change from baseline, and direct comparisons between active and sham at either single time point were not significant. Accuracy, by contrast, improved from baseline to post-stimulation across both conditions, with no stimulation-specific effect, a pattern the authors attribute to the well-documented sensitivity of the PASAT to repeated task exposure. Because reaction time fell without any loss of accuracy, the findings argue against a simple speed-accuracy trade-off and instead point to improved response efficiency.
The electrophysiological data added a neural dimension to the behavioral effect. The researchers focused on three event-related potential components: the N200, a frontal negativity linked to conflict monitoring and inhibitory control; the P300, which reflects attentional resource allocation and working memory updating; and the late slow wave, associated with sustained executive engagement. After active tRNS, frontal N200 amplitudes became significantly less negative, shifting from a baseline mean of −0.73 microvolts to 0.65 microvolts post-stimulation, an effect that survived false discovery rate correction. Frontal P300 amplitudes also became significantly more positive after active stimulation, rising from −0.12 to 1.12 microvolts. Neither component changed significantly under sham, and no stimulation-specific effects appeared at the parietal electrode cluster for any component.
Strikingly, the most reliable ERP changes appeared over frontal sites even though the stimulation was applied to the parietal cortex. The authors interpret this spatial dissociation as consistent with the idea that non-invasive brain stimulation can influence distributed, functionally connected control networks rather than producing strictly local effects. The posterior parietal cortex is a central hub within the frontoparietal control network, maintaining dense reciprocal connections with prefrontal regions that support top-down attention and executive control, so modulation at the parietal node could cascade into altered processing expressed at frontal electrodes. Computational modeling studies of transcranial electrical stimulation support the possibility of such network-level effects on both local and remote connected cortical areas.
A correlation analysis tied the neural changes to the behavioral ones. Among participants with usable data in both domains, greater reductions in reaction time after active tRNS were significantly associated with greater increases in frontal P300 amplitude, with a Pearson correlation of −0.45 that remained significant after Bonferroni correction. In other words, the individuals who sped up the most also showed the strongest enhancement of the frontal component linked to attentional allocation and rapid updating. Reaction time changes were not reliably associated with frontal N200, frontal late slow wave, or any parietal measures. The late slow wave itself showed only a general main effect of time at both frontal and parietal clusters, without a stimulation-by-time interaction, so the authors caution that those findings may reflect general time-related changes rather than stimulation-specific modulation.
The study has clear boundaries. The sample consisted entirely of healthy young adults, so the results cannot be generalized to clinical populations with cognitive control impairments, even though the PASAT is widely used in conditions such as traumatic brain injury and multiple sclerosis. Reaction times were measured via key presses synchronized with oral responses rather than direct vocal onset detection, only post-stimulation effects were examined, and the relatively large sponge electrodes produced a diffuse electric field with limited spatial focality, with no alternative stimulation site included to establish anatomical specificity. The authors also note that because tRNS can induce broader changes in cortical excitability, the ERP findings cannot fully distinguish component-specific cognitive modulation from a general excitability shift. No significant adverse effects were reported, and sensation ratings did not differ between conditions.
Within those limits, the study offers preliminary electrophysiological evidence that parietal tRNS can influence task-related neural activity expressed far from the stimulated electrodes, and that ERP components may serve as measurable markers of stimulation-related performance changes. Future work, the authors suggest, should use voice-key or acoustic onset recording, online stimulation during task performance, individually calibrated task difficulty, more focal stimulation montages, and source-resolved or multimodal neuroimaging to clarify how parietal noise stimulation reshapes the dynamics of the frontoparietal control network under high cognitive demand.
Subject of Research: Effects of bilateral parietal transcranial random noise stimulation on PASAT performance and event-related potentials
Article Title: Bilateral parietal tRNS improves processing speed on the paced auditory serial addition test (PASAT): behavioral and ERP evidence
Article References: Cui, J., Chen, H., Wang, X., & Cong, F. (2026). Bilateral parietal tRNS improves processing speed on the paced auditory serial addition test (PASAT): behavioral and ERP evidence. Behavioral and Brain Functions, 22(1), Article 31. https://doi.org/10.1186/s12993-026-00357-7
Image Credits: AI Generated
DOI: 10.1186/s12993-026-00357-7
Keywords: tRNS, transcranial random noise stimulation, posterior parietal cortex, PASAT, reaction time, event-related potentials, N200, P300, EEG, cognitive control, working memory, non-invasive brain stimulation
News Source: Cassandra Pierce. (October 29, 2026). Brain Zapping Over Parietal Regions Speeds Responses on Demanding Memory Test. Scienmag.
