April 09, 2019
Age-related decline in working memory can be reversed using transcranial alternating current stimulation (tACS) to synchronize rhythmic brain circuits, new research suggests.
Investigators at the Center for Systems Neuroscience at Boston University made two discoveries.
First, in older adults, deficits in working memory stem from specific brain circuits becoming uncoupled or disconnected. Second, applying extremely weak electrical current in a very specific way can reconnect, or resynchronize, those faulty brain circuits and rapidly boost working memory function.
"These findings are important because they not only give us new insights into the brain basis for age-related working memory decline, but they also show us that the negative age-related changes are not unchangeable and that we can bring back the more superior working-memory function that you had when you were much younger," study investigator Robert Reinhart, PhD, and doctoral student John Nguyen told reporters attending a press briefing.
The study was published online April 8 in Nature Neuroscience.
Working memory is a "fragile and precious resource" that declines with advancing age and is of central importance in normal age-related cognitive decline. One of the major goals in the field of neurocognitive aging is to understand the brain regarding the decline in working memory with aging, said Reinhart.
To that end, Reinhart and Nguyen studied 42 healthy adults aged 20 to 29 years and 42 healthy adults aged 60 to 76 years. All of the participants completed a working memory task while brain activity was being monitored by electroencephalography.
In a blinded fashion, participants received 25 minutes of either active tACS that simultaneously targeted the prefrontal and temporal regions or sham stimulation sessions on different days.
In the younger adults, while performing the working memory task, there was an increase in interactions between theta and gamma rhythms in the left temporal cortex and an increase in synchronization of theta rhythms in the frontotemporal regions.
Before any brain stimulation, the older adults were slower and less accurate than the younger adults on the working memory task. For the older adults, while receiving active brain stimulation, working-memory test scores improved to the levels of the younger participants. The effect was rapid and lasted for at least 50 minutes after the stimulation was stopped.
Reinhart believes tACS works by synchronizing brainwaves in the prefrontal and temporal cortex. The improvements in task accuracy correlated with increased interactions between theta and gamma in the left temporal cortex, and there was an increase in synchronization of theta brainwaves between tge left temporal and the prefrontal cortex, he noted.
Reinhart also noted that problems with working memory and functional connectivity are hallmarks of neurologic disorders such as Parkinson disease, schizophrenia, and autism and that noninvasive stimulation could prove helpful for patients with these disorders.
"Our hope is that this work will help lay basic science groundwork for really an entirely new avenue of research where we develop noninvasive new neuroscience tools to help treat people who are suffering from brain disorders," he said.
Commenting on the findings for Medscape Medical News, Gary Small, MD, director of the University of California, Los Angeles (UCLA) Longevity Center and professor of psychiatry and biobehavioral sciences at the UCLA School of Medicine, said that the inability of key neural circuits to communicate effectively clearly contributes to age-related cognitive decline.
"This report offers some promising evidence that could eventually lead to an intervention that helps to maintain working memory as people age," he said.
Also commenting on the findings for Medscape Medical News, Flavio Fröhlich, PhD, assistant professor of psychiatry, cell biology and physiology, biomedical engineering, and neurology, University of North Carolina at Chapel Hill, said the research makes an important contribution to the literature and shows that "very weak electric current, if smartly timed, can enhance brain rhythms and thereby improve cognitive performance.
"We've known for a while that tACS can modulate brain activity and also how different parts of the brain interact with each other. We've also known that manipulating how different brain regions relate to each other with tACS can enhance certain types of memory performance," he said.
"What's exciting about this study is the application to an older population. It's a carefully done study by not only applying stimulation, seeing changes in performance, but also looking inside the box and understanding how through stimulation activity patterns have changed," Frohlich added.
However, he noted, it's largely unknown whether repeat stimulation would generate changes in brain activity patterns that would persist.
The study was supported by the National Institutes of Health. The authors and Small have disclosed no relevant financial relationships. Fröhlich is the founder of Pulvinar Neuro.
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SOURCE: Medscape, April 09, 2019. Nat Neurosci. Published online April 8, 2019.