Timing of high-definition transcranial direct current stimulation to the nondominant primary motor cortex fails to modulate cortical hemodynamic activity and improve motor sequence learning.

The study included only 20 healthy adults, which may limit the generalizability of the null findings to clinical populations such as stroke survivors. The interventionist was not blinded to the stimulation condition, although the interventionist did not manage the device settings directly. The fNIRS system lacked short separation channels, meaning the measured brain activity could have been contaminated by changes in blood flow in the scalp caused by the stimulation electrodes. The stimulation intensity was low (1 mA), and it is unclear if higher intensities or multiple sessions would produce different results.

The study was funded by several Shanghai municipal and national health and science programs. No commercial conflicts of interest were reported.

Do not conclude that tDCS is ineffective for all motor learning or in all populations. This null result applies specifically to a single session of low-intensity stimulation in healthy older adults; the authors note that larger trials and different parameters are needed before ruling out benefits in other contexts.