For people who’ve lost some mental sharpness, to either aging or disease, a technique that gently “zaps” the brain circuitry is showing early promise.
That’s according to a new analysis of more than 100 studies assessing the technique, called transcranial alternating current stimulation, or tACS. It involves using electrodes on the scalp to send weak electrical pulses to specific brain areas.
The premise behind tACS is based on the fact that brain activity naturally occurs in rhythmic patterns, or oscillations. Specific brain oscillations have been tied to various brain functions and states, with abnormal rhythms linked to a range of symptoms, including problems with memory and thinking.
The electrical pulses from the tACS device essentially “nudge” the brain to find its rhythm again, said Shrey Grover, one of the researchers on the analysis.
In early studies, tACS has shown promise for easing a range of symptoms from neurological and psychiatric conditions such as Parkinson’s disease, depression and obsessive-compulsive disorder.
Researchers also think it holds promise for improving problems with memory and thinking related to mild cognitive impairment — a condition that affects many older adults and, in some cases, progresses to dementia.
But for now, tACS remains “investigational.” It’s not approved by the U.S. Food and Drug Administration for treating any medical condition, stressed Grover, a doctoral student in brain, behavior and cognition at Boston University.
“tACS is promising,” he said. “But we’re still some years away from having it widely available.”
The technique is just one form of so-called neuromodulation — therapies that work by altering nerve activity.
During tACS, electrodes are placed on the head at specific locations. Those electrodes are connected to a small device that delivers a weak electrical current to the brain.
Research so far has shown the procedure to be safe. During the first minute or two, Grover said, some people sense an itch or “tapping” at the site of the stimulation, or a temporary “flickering” in their vision.
As for effectiveness, studies have come up with promising signals, but they have also been mostly small and very short-term.
For the new analysis, published May 24 in Science Translational Medicine, Grover and his colleagues pulled together published studies dating back to 2006 that have looked at the effects of tACS on cognition. That included abilities such as attention, short-term memory, reasoning and problem-solving.
They found 102 studies in all that involved a range of participants: healthy adults, both old and young, as well as people with mild cognitive impairment or medical conditions that can affect cognition — including Parkinson’s, major depression and schizophrenia.
In each study, tACS was compared against a “sham” procedure where the electrodes delivered no or limited stimulation. During all sessions, participants performed some kind of cognitive exercise so their improvement (or lack thereof) could be tracked.
Overall, the researchers found, people who received tACS typically showed some improvement in their cognitive performance — either during or right after the procedure. That was true of healthy people and those with medical conditions. However, Grover said, there were too few studies of each individual condition to determine whether tACS was more effective for some than others.
One of the big caveats, Grover said, is that the studies looked only at people’s short-term mental acuity in the lab.
“Are these effects strong enough to make an impact on someone’s life?” he said. “Are the effects sustained?”
But even before those real-world questions can be answered, there are more fundamental ones, Grover said. For example, how can tACS be optimally delivered? Can the location of brain stimulation be refined? How long should each session be? How should sessions be timed?
Leigh Charvet is a clinical neuropsychologist at NYU Langone Health in New York City, who is studying a similar neuromodulation technique called transcranial direct current stimulation (tDCS).
That technique is being studied for depression and anxiety, and for improving movement, speech and cognitive symptoms related to conditions such as Parkinson’s, stroke and multiple sclerosis.
The brain stimulation itself is not enough, Charvet said. It’s done with a “paired activity.” So if the goal is to improve cognition, the stimulation is applied during mental exercises.
Charvet agreed that researchers are still working out the optimal ways to apply the technologies. And then there’s another critical question: Whom do you treat?
“What threshold are we talking about?” Charvet said.
Should a healthy person with a fuzzy memory get a few brain zaps? To Charvet, the answer is no. But an older person with mild cognitive impairment might benefit. (Waiting until someone has full-blown dementia would likely be too late, she noted.)
The studies in the current analysis were done between 2006 and 2021. More recently, Grover said, some research has looked at the effects of tACS over a longer time span.
In a study published last year, he and his colleagues followed 150 older adults who received either tACS or a sham version for four days in a row. Most had what was considered normal age-related memory decline. After their tACS sessions, though, participants typically showed an improvement in short-term memory that lasted a month.
While both researchers stressed that a lot of work remains, at-home brain stimulators — perhaps unsurprisingly — are already readily available for consumers to buy online.
“We advise against that,” Charvet said.
The U.S. National Institute of Mental Health has more on brain stimulation techniques.
SOURCES: Shrey Grover, PhD student, brain, behavior and cognition, Boston University; Leigh Charvet, PhD, clinical neuropsychologist, NYU Langone Health, and professor, neurology, NYU Grossman School of Medicine, New York City; Science Translational Medicine, May 24, 2023, online