This is pretty fascinating. If I’m getting it, it implies that for this particular brain function there is an upward bounded capability. If you’re already there (say, genius level) tDCS won’t improve your performance, but it will if you’re not already wired at the upper bound! I know from my CambridgeBrainScience.com tests, that I’m especially weak in the VSTM (visual short-term memory) area. [Unfortunately there’s a paywall around this and most other journal paper.] Paper originates from the Institute of Cognitive Neuroscience at the National Central University, Taiwan.
Here we show that artificially elevating parietal activity via positively charged electric current through the skull can rapidly and effortlessly improve people’s VSTM performance.
…The high performers, however, did not benefit from tDCS as they showed equally large waveforms in N2pc and CDA, or SPCN (sustained parietal contralateral negativity), before and after the stimulation such that electrical stimulation could not help any further, which also accurately accounts for our behavioral observations. Together, these results suggest that there is indeed a fixed upper limit in VSTM, but the low performers can benefit from neurostimulation to reach that maximum via enhanced comparison processes, and such behavioral improvement can be directly quantified and visualized by the magnitude of its associated electrophysiological waveforms.
via Unleashing Potential: Transcranial Direct Current Stimulation over the Right Posterior Parietal Cortex Improves Change Detection in Low-Performing Individuals.