Can transcranial brain stimulation help refine memory? : Coups

This is an unfortunate fact: as we age, we tend to forget more and more.

Aging brains struggle particularly with working memory. Called the Mind Workshops, working memory allows us to store useful information for a few seconds and use it in different areas of the brain to help solve problems, plan or make decisions.

Researchers are trying to understand why this ability fades with age and if we can slow down or reverse this decline.

A major hypothesis is that working memory works by very distant brain zones that are triggered synchronously. When two zones are on the same wavelength of the brain, the communication is close and the working memory functions transparently.

But as we get older, these brain regions begin to fall out of balance and these once closely connected regions are no longer on the same wavelength. A study published Monday in Nature Neuroscience demonstrates a link between these incompatible brain rhythms and a decrease in working memory in the elderly and shows that a precise form of electrical stimulation applied to the scalp can allow these brain areas to synchronize.

Applied to the brain via an encrusted cap of electrodes, an experimental form of transcranial brain stimulation delivers an alternating current to a small group of neurons to push them to a specific wavelength. Imagine two giant pendulums swaying at different rhythms. Brain stimulation pushes each pendulum with a pair of electric hands that grow at the same frequency, making them synchronize and swing synchronously.

What happens when these electric hands synchronize badly matched areas of the brain? In the study, the performance of older people on a working-memory measure improved compared to younger adults and the effects lasted at least 50 minutes after stimulation.

"In regards to this task of working memory, we created the brain of a 70-year-old man like that of a 20-year-old man," said Robert Reinhart, neuroscientist of the University of Toronto. Boston University who led the study. He says it's the first time that a study shows that disconnected brain areas are related to working memory deficits in the elderly and that transcranial stimulation can bring them back to sync.

Jared Cooney Horvath, a neuroscientist at the University of Melbourne, who generally describes himself as skeptical about brain stimulation research, found this study compelling. "In short, I did not like this paper, but it seems to show exactly what it's supposed to show"

The application of a weak electric current on the scalp is not a new concept. This goes back as far as in ancient Rome, where Scribonius Largus, physician to Emperor Claudius, had laid an electric torpedo fish on the heads of patients with headaches.

Transcranial electrical stimulation is the modern version of electric fish. In the early 2000s, it sparked renewed interest. Communications showed how a form of treatment, applying a small unidirectional current, could excite or calm large amounts of neurons. Other works have suggested that this could improve engine learning. Subsequent research has shown that a low electric current could synchronize the activity of neuron populations, causing them to fire together. Many people on the ground began to explore how refinement of this synchronized activity could induce behavioral changes, such as increased memory.

The research also generated an active and potentially misguided DIY community of brain stimulation enthusiasts who exchange protocols on Reddit forums to improve learning or relieve depression. Many experts advise against this, saying that we still have a lot to learn about the real impact of non-invasive brain stimulation on the brain, and that inappropriate use could be dangerous.

That's why studies like this are so important, says Marom Bikson, a biomedical engineer at the City College of New York. Bikson did not participate in this study, but developed the brain stimulation technique used by the authors, a more targeted form of brain stimulation known as transcranial AC or HD-tACS AC stimulation. These authors undertook rigorous testing of the biological mechanism underlying memory loss – inadequate brain rhythms in the temporal and prefrontal cortex – and how stimulation could affect them.

To do this, the researchers assigned a group of young adults and older adults a task of working memory while they were connected to an EEG, which makes it possible to measure brain wave activity in both regions. An image flashed on a screen, say a fire mouth, then the subject would see a series of other images and should distinguish the images already seen from the news.

As expected, older adults were significantly slower and less accurate than younger adults on the test, and this poorer performance was associated with a lack of linkage. brain rhythms.

But to show that these desynchronized circuits are actually causing work memory deficits, researchers had to go further. They had to show that synchronizing these areas improves the performance of the working memory.

That's precisely what researchers have done using HD-tACS to exploit the existing oscillations of specific brain areas and get them off the ground.

In addition, researchers could adapt the frequency to each individual based on the collected EEG data. Using a double-blind configuration, in which no one involved knew who was being stimulated, researchers placed a special cap on all participants during the memory exercise.

Older adults who received brain stimulation were as accurate as younger adults during the 25-minute stimulation period and continued to show improved performance for 50 minutes after the end of stimulation.

When Reinhart examined the EEGs of older adults who were on treatment, he found that their temporal and prefrontal cortex were in phase, just like a younger brain.

"Not only did we find that the decrease in working memory is due to the disconnection of specific brain circuits, but we have also been able to non-invasively stimulate these defective brain circuits in the elderly to quickly stimulate their brain and their memory functions, "says Reinhart.

The researchers also reversed the stimulation delivered to younger adults, temporarily desynchronizing their rhythms, and found that their working memory was in decline, demonstrating that synchronization between these areas of the brain was essential for working memory.

Finally, Reinhart took the poorest young adults from the first experience and stimulated their brains to synchronize these areas of the brain. The result? A boost in performance.

"I'm really excited about this document," said Bikson. "This goes in the direction of establishing a rigorous scientific basis for this type of brain stimulation technique."

Horvath and Reinhart warn both of you that there is still a lot of work to do before you can attach electrodes to your head and wait for a cognitive boost. "Although these results are convincing, it is only a group study," Horvath said. "I would like this to be replicated by other labs and expanded to test other aspects of working memory."

Horvath says that this type of performance gain, while statistically significant, may not be clinically significant. "In each trial, young adults got about 24 correct images out of 26, while older adults got about 22 out of 26 and were boosted to about 24 with stimulation," he says. "I would wonder if this bump has real or clinical value."

In addition, further research is needed to determine whether these increases last long after stimulation. "At some point, you want to enjoy these benefits without wearing an electrode cap," says Bikson.

This study did not test participants 50 minutes after stimulation, so it's possible that they had stimulation that lasted longer, according to Reinhart. He says that other studies on brain stimulation have revealed changes in cognition that last days or even weeks. But is this stimulation simply a temporary crutch? Or does it induce lasting changes in the brain?

"There is still a lot of research to be done to answer this question," says Reinhart. "It's still exciting to think that perhaps we could simply apply this stimulation and synchronize your brain rhythms so that you can maintain yourself, giving a lasting boost to cognition."

Jonathan Lambert is an intern at NPR's Science Desk. You can follow him on Twitter: @evolambert