Gentle Brain Stimulation Improves Short-Term Memory

By synchronizing brainwaves, this therapy reversed age-related memory decline

A woman stands and holds a device toward another woman who is seated and wearing a white cap connected to many wires.
Photo: Boston University
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Electrical stimulation was once a last resort for the brain. Electroconvulsive therapy, for example, was developed to treat severe depression only after other therapies had failed.

But times change and now we find ourselves in the era of gentle, non-invasive brain stimulation. Electrodes on the scalp have been shown to safely nudge the brain with soft jolts of electricity and are being tested to treat Alzheimer’s disease, alleviate obsessive-compulsive disorder, and even boost memory storage.

In a paper published today in Nature Neuroscience, researchers at Boston University show that electrical stimulation can also improve working memory—our ability to briefly store information while thinking, reasoning, or problem solving. Called the “sketchpad of the mind,” working memory is a linchpin of human consciousness, and it declines as we age.

After a 25-minute stimulation session involving synchronizing brain waves between two frontal areas of the brain, adults aged 60 to 76 showed marked improvements in working memory tasks—to the point that they performed on par with younger adults.

“We can reconnect, or resynchronize, those faulty brain circuits in the brains of the elderly and then rapidly boost their working memory function,” said study author Robert Reinhart, during a press briefing about the work.

The results are important for two key reasons. First, they support the theory that age-related brain decline is due to dysconnectivity between brain areas. Second, they suggest that the decline isn’t permanent, and that it is possible to restore youthful brain function.

Reinhart and BU graduate student John Nguyen invited two sets of adults—42 younger adults (aged 20 to 29) and 42 older adults (aged 60 to 76)—to participate in a battery of tests of working memory, such as recognizing if an image changed after a brief delay.

With no brain stimulation, the younger adults were faster and more accurate than the older adults.

Then, Reinhart turned on the tech—a skull cap full of electrodes to perform high-definition transcranial alternating-current stimulation (HD-tACS). In this study, HD-tACS applied a small (just 1.6 milliamps) alternating current to rhythmically sync the activity of the prefrontal and temporal areas of the brain. Like a conductor synchronizing instruments in an orchestra, the current gently guided populations of neurons to fire simultaneously.

Each stimulation session was tailored to each participant’s individual brain dynamics, says Reinhart—so if a person’s brain oscillates at 6.8 Hertz, the cap was tuned to that wavelength. Some participants reported tingling and itchiness during the session.

After the session, they again tested working memory, and the older adults’s skills had improved to that of younger adults. In fact, even the younger adults who weren’t great at the tasks got better. That boost in function lasted for at least 50 minutes after the stimulation had ended. Based on similar studies, the benefit likely extends up to several hours, says Reinhart, though the total duration was not measured in the current study.

Deficits in working memory are not exclusive to aging—they are also central to brain disorders such as schizophrenia, Alzheimer’s, attention deficient disorder, and more, says Reinhart.

“Our hope is that this work will help lay a basic science groundwork for entirely new avenues of research where we develop non-invasive neuroscience tools to help treat people suffering from brain disorders,” he says. 

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