By the end of the four days, those who’d had their brains stimulated improved their performance by around 50 to 65% and remembered around four to six extra words from the list of 20, on average, says Reinhart. “It’s very impressive,” says Roi Cohen Kadosh, a cognitive neuroscientist at the University of Surrey, who was not involved in the study.
“We can watch the memory improvements accumulate … with each passing day,” says Reinhart, who, along his colleagues, published the findings in the journal Nature Neuroscience on Monday.
The greatest improvements were among those who had the worst cognitive function at the start of the study. This suggests that the technique might one day be helpful for people with memory disorders such as Alzheimer’s disease or other dementias, says Reinhart.
When Reinhart’s team swapped the frequencies, targeting the front of the brain with low frequencies and the back of the brain with high ones, there was no improvement in either short- or long-term memory. This suggests that the type of stimulation must match the natural brain waves in order to work.
Reinhart and his colleagues only checked in on their volunteers a month after they did the experiment, and they don’t know if the improvements lasted beyond that point. And while the study found that the volunteers were better at remembering words from a list, Reinhart doesn’t know if their memories improved more generally, or if the stimulation improved their lives in any way.
“The effects are really specific, and not something that would benefit someone who would want to improve their memory [more generally],” says Cohen Kadosh. He points out that people who want to remember things for an exam, for example, don’t just want to remember the first and last things they read—they need to remember everything. “We need to see if there is really an effect … in everyday life functions,” he says. Bikson agrees this is a valid concern—some “brain training” games promise to boost a player’s cognition, but research suggests that in fact players only get better at playing the game, and don’t see wider benefits. Reinhart’s approach, though, is different, he points out. “If you are stimulating brain networks that are generally involved in some aspect of cognition … that gives credence to the [idea that the benefits] could generalize,” he says.