Online anodal tDCS of posterior parietal cortex enhances tactile working memory in time- and performance-dependent manner
A double-blind, sham-controlled study found that anodal transcranial direct current stimulation (tDCS) over the left posterior parietal cortex improved tactile spatial working memory accuracy by approximately 5% in healthy adults. The effect emerged gradually, roughly eight minutes into the 15-minute stimulation session, and was most pronounced in participants who started with lower baseline performance. The findings clarify both the timing and the individual-difference factors that shape cognitive benefits from non-invasive brain stimulation.
Researchers tested whether online anodal tDCS applied at 2 mA over the left posterior parietal cortex (PPC) could enhance performance on a tactospatial working memory task in 32 healthy adults using a double-blind, within-subject crossover design. Participants completed two counterbalanced sessions — one with active stimulation and one with sham — while performing a retro-cued delayed match-to-sample task involving vibrotactile patterns delivered to the left index finger. Using a sliding-window analysis combined with cluster-based permutation testing, the team found that active stimulation produced a statistically significant, gradual improvement in working memory accuracy relative to sham, with an effect size of Hedges' g = 0.43 and a roughly 5% performance gain. Critically, this improvement did not appear immediately but emerged around eight minutes after stimulation onset, suggesting that tDCS effects build incrementally during ongoing stimulation rather than acting instantaneously. The benefits were also strongly baseline-dependent: individuals with lower initial working memory performance showed the largest gains, while high performers showed little to no improvement. These results extend prior work on fronto-parietal networks in spatial working memory by demonstrating that PPC stimulation can modulate the tactile, not just visual, domain. The study highlights that both timing of assessment and participants' starting cognitive state are critical variables in interpreting tDCS outcomes.
What's missing
The study was conducted on healthy adults only, leaving open whether these effects generalize to clinical populations with working memory deficits. The mechanism by which anodal tDCS gradually increases cortical excitability over the stimulation window is not fully established, and it is unclear whether the ~5% accuracy gain persists beyond the post-stimulation phase or has any functional real-world significance. As a preprint on bioRxiv, the findings have not yet undergone formal peer review.
What different sources said
- bioRxivCenter
Time- and performance-dependent enhancement of tactospatial working memory caused by online anodal tDCS of the posterior parietal cortex
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