Brain Stimulation Leads to Long-Term Memory Improvements

Human memory declines as we age, but one day researchers may be able to reverse this trend with a simple, non-pharmaceutical approach.

In a study published on August 22, Nature Neuroscience¹Robert Reinhardt, a cognitive neuroscientist at Boston University in Massachusetts, and his colleagues found that repeated zapping of the brains of adults 65 years and older with low current for several days resulted in memory improvements lasting up to a month. We have proved that

Previous research has suggested that long-term memory and ‘working’ memory, which allows the brain to store information temporarily, are controlled by different mechanisms and parts of the brain. Using this research, the researchers found that stimulation of the dorsolateral prefrontal cortex (an area near the front of the brain) with high-frequency current improved long-term memory and stimulated the inferior parietal lobe further back in the brain. We have demonstrated that , improved working memory with low-frequency currents.

“Their results look very promising,” says neuroscientist Ines Violante of the University of Surrey in Guildford, England. “They really put their accumulated knowledge in this area to good use.”

memory boost

Reinhart’s team conducted a series of experiments on 150 people aged 65 to 88 using a noninvasive method of stimulating the brain known as transcranial alternating current stimulation (tACS). A memory task was performed in which the experimenter was asked to recall a list of her 20 words read aloud. Brain stimulation occurred for the entire duration of the task, which lasted 20 minutes.

After undergoing this protocol for four consecutive days, participants who received high-frequency stimulation of the dorsolateral prefrontal cortex improved their ability to recall words from the beginning of a list, a task that relies on long-term memory. Low-frequency zapping to the medial parietal lobe enhanced participants’ recall of items further down the list, including working memory. The participant’s memory improved during her four days, and the improvement persisted after her one month. People who had the lowest levels of general cognitive function before the study experienced the greatest memory improvements.

Alter the frequency and brain region (e.g., apply high-frequency stimulation to the parietal lobe), or use a ‘sham’ protocol that applies current briefly at the beginning and end of the task to mimic sensations in the brain. Stimulation did not improve memory.

persuade skeptics

Simon Hanslmayr, a cognitive neuroscientist at the University of Glasgow, UK, said: He says, like other scientists, he was skeptical that tACS could bring about meaningful changes in cognition. One of the problems is that the currents produced by tACS devices are much weaker than those produced by other methods of stimulating the brain, so tACS devices may not be sufficient to alter brain function. It was not always clear whether electricity could be transmitted to the brain. But the study’s authors convincingly showed that their protocol was associated with “consistent and very strong memory improvements,” says Hanslemeyer.

Hanslmayr adds that there were several factors that made the study unique. One is that the author applied his tACS for several days in a row. Previous studies have typically been applied in a single session only. Another is that the experiment involved people over the age of 65. Most others are aimed at young students with good memory function. These factors, he says, may help explain why the authors were able to obtain such impressive results.

Some questions remain. To what extent the benefits of brain stimulation can be generalized to other types of memory tasks, and whether the improvement in memory persists beyond his month, are two of his key points that the team will address in future studies. It’s a problem, says his co-author Shrey Grover. A cognitive neuroscientist in Reinhardt’s lab.

The team is also expanding its research to see if tACS can help people with conditions such as Alzheimer’s disease, he added. “We hope to extend this research in meaningful ways and provide more information about how the brain works.”