The effect of high-definition transcranial direct current stimulation intensity on motor performance in healthy adults: a randomized controlled trial.
Ohad Lerner, Jason Friedman, Silvi Frenkel-Toledo
PMID 34174914WHAT IT FOUND
In healthy adults, 1.5 mA brain stimulation improved movement speed immediately after a task, while 2 mA did not.
Neither intensity made people faster than the sham group at any single point. The 2 mA dose appeared to block the learning seen in the other groups.
Key findings
01Movement time did not differ between the 2 mA, 1.5 mA, and sham groups at any time point.
02The 1.5 mA group showed a significant reduction in movement time from pretest to posttest, which was greater than the change in the 2 mA group.
03Reaction time improved across all groups from pretest to retest, with no significant differences between the stimulation intensities.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study was conducted on healthy adults, so results may not translate directly to patients with neurological conditions like stroke. Blinding may have been compromised because participants in the active groups reported higher levels of discomfort than those in the sham group. The task difficulty may have been too low to reveal clear differences between the stimulation intensities. Individual anatomical differences in brain shape and fluid distribution can affect how much current actually reaches the brain, which was not controlled for in the analysis.
Declared interests
The authors declared no competing interests. The study was supported by non-U.S. government funding.
The easy way to misread this
Do not interpret the 1.5 mA group's improvement as proof that this dose is superior to sham or that it causes better learning. The primary comparison showed no significant difference between any of the three groups at any single time point. The 1.5 mA group simply improved more than the 2 mA group, which appeared to inhibit learning.