January 14, 2022
Inhibitory control is an essential cognitive control function whereby the prefrontal cortex blocks planned motor actions or interrupts motor actions already initiated by other parts of the brain. For example, someone might instinctually reach for a candy bar but then put it back upon thinking that eating it would conflict with a higher-level goal of cutting down on sugar consumption. Impairment of inhibitory control is a known characteristic of several psychiatric disorders, including ADHD.
Any generally safe treatment with the ability to at least partially reverse such impairment would therefore be useful. Researchers are currently experimenting with transcranial direct current stimulation, a non-invasive brain stimulation technique that uses a weak electrical current to stimulate specific regions of the brain.
What, then, do we know so far about its potential effectiveness for improving inhibitory control?
A team of experts at the University of Tübingen in Germany conducted a comprehensive search of the peer-reviewed medical literature to find out. They then performed a meta-analysis of 45 studies with a combined total of over 1,600 participants. All but four of the studies used sham or other active controls.
The overall meta-analysis found a significant but small improvement in response inhibition. But it also found evidence of publication bias. Adjusting for publication bias reduced the effect size in half, to a tiny but still significant improvement.
The meta-analysis relied on two behavioral tasks that require inhibitory control to measure response inhibition: the go-/no-task, and the stop-signal task. Separating these, there was no significant improvement in the go/no-go task performance. All the improvement was concentrated on the stop-signal task.
The authors noted, "A potential limitation of this meta-analysis is that we could not exhaustively model-dependent relationships between moderator variables (e.g., tDCS polarity and electrode placement)," and "Further high-quality studies are needed to investigate potential interactions between technical and functional parameters in tDCS research."
Philipp A.Schroeder, Tobias Schwippel, Ines Wolz, Jennifer Svaldi, "Meta-Analysis Of The Effects Of Transcranial Direct Current Stimulation On Inhibitory Control," BrainStimulation(2020),https://doi.org/10.1016/j.brs.2020.05.006.