We all have our little tips and tricks to help our brains function just a little bit better. Coffee and energy drinks. B vitamins and ginseng. Or, in the case of a growing group of scientists and DIYers, running a weak electrical current into the brain.
Transcranial direct-current stimulation was originally developed to help patients who had suffered from brain injuries, like a stroke. It delivers a constant, low current to a specific area of the brain via electrodes stuck to the patient's scalp.
In 2012, Dr Roi Cohen Kadesh of the University of Oxford's Department of Experimental Psychology found that tDCS increases cognitive ability and that treated patients still showed heightened cognitive ability six months after receiving tDCS.
But a new study published in the journal Behavioural Brain Research showed that the results of the treatment are mixed.
"It would be wonderful if we could use tDCS to enhance cognition because then we could potentially use it to treat cognitive impairment in psychiatric illnesses," said Flavio Frohlich, PhD, study senior author and assistant professor of psychiatry, cell biology and physiology, biomedical engineering, and neurology at the University of North Carolina at Chapel Hill School of Medicine.
"So, this study is bad news. Yet, the finding makes sense. It means that some of the most sophisticated things the brain can do, in terms of cognition, can't necessarily be altered with just a constant electric current."
To test the theory, Frohlich and team, including first author graduate student Kristin Sellers, started by having 40 healthy adults sit the standard WAIS-IV intelligence test, which tests for verbal comprehension, perceptional reasoning, working memory and processing speed.
A week later, these adults were split into two groups. One group received tDCS, targeting the areas of the frontal cortex targeted by previous tDCS studies. The other group was given a sham tDCS treatment -- a placebo, believing they had received the real treatment.
All study participants then retook the test. It was expected that all of the scores would improve, since the study participants had already taken the test once; but the results surprised the research team. The placebo group's scores increased by 10 points on average; yet the tDCS group's scores only increased by an average of six points.
The biggest difference was the perceptional reasoning section of the test. While the other three sections saw improvements about on a par between both groups, the tDCS group was markedly poorer at tasks such as spatial reasoning, non-verbal abstract problem solving, visual abstract processing and inductive reasoning.
According to Frohlich, a different type of electrical stimulation may yield better results: transcranial alternating current stimulation, which uses an alternating current, rather than a constant current, to stimulate the brain. Earlier this year, Frohlich's team announced that it had found tACS improved the brain's creativity with a proof-of-concept study.
Studies on tDCS, which started to become more common in 2000 with a study published in the Journal of Physiology, have had problems, Frohlich said. Some were not properly double-blinded, or properly placebo-controlled. Others used too small a sample -- 10 people or fewer.
Even with Frohlich's team's study, there's still work to be done.
"Our findings do not preclude the possibility that other tDCS paradigms may be less harmful or even beneficial. However, it is time to make sure that everybody uses gold standard, placebo-controlled, double-blind study designs. Also, our study demonstrates the importance of more research on how stimulation interacts with brain activity," he 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."