Transcranial Direct Current Stimulation May Impair IQ

The authors recommend that more research be done on tACS (transcranial alternating current stimulation) instead.

A new study from the University of North Carolina School of Medicine warns against the mass adoption of transcranial direct current stimulation (tDCS), showing that the weak electrical current may actually have detrimental effects on IQ.

The study, published in Behavioural Brain Research, adds to mounting evidence that tDCS may not be the “magic” treatment that some have made it out to be, especially for uses like cognitive enhancement.

Flavio Frohlich, PhD, and colleagues evaluated the effects of tDCS on 40 healthy adults, each of whom took the standard WAIS-IV intelligence test to evaluate pre-treatment IQ. The test evaluates verbal comprehension, perceptional reasoning, working memory, and processing speed.

One group of participants received standard tDCS treatment for 20 minutes and the placebo group received sham stimulation. Participants’ IQ scores were reevaluated after the treatment, and all showed an improvement in IQ score, however those who received the sham treatment saw their scores increase by, on average, 10 points, while those who received tDCS only saw scores improve by an average of nearly six points. Scores for cognitive tests were similar among all participants accept for perceptual reasoning, in which those who received tDCS scored much lower than those who received the sham treatment.

Within perceptual reasoning, researchers observed the biggest difference between the groups in matrix reasoning, in which participants viewed two groups of symbols and had to find the one symbol missing from the other group.

Frohlich, who pointed out that previous studies on tDCS have been poorly designed, stressed that more, long-term studies on the effects of tDCS need to be completed before the technology is adopted in more casual treatment settings.

“There could be dangerous consequences, especially if tDCS is used daily,” Frohlich said. “Ours was an acute study. We don’t know what the long-term effects are. There is so much more we need to understand before tDCS is ready for home use without medical supervision”

Frohlich recommends that more research be done on tACS (transcranial alternating current stimulation) since it targets the brain’s natural electrical alpha oscillations instead of brain structures themselves. 


  1. Sellers KK et al. Behav Brain Res. 2015; doi:10.1016/j.bbr.2015.04.031.