All brain processes, including memory, rely on the transfer of information throughout the brain by electrical and chemical signals. Memory performance is reduced in old age and in diseases such as Alzheimer's. This reduced performance may be due to the inability of neurons to properly communicate with each other across different brain regions. In a new paper in Nature Neuroscience, researchers used a weak electrical stimulation procedure across the skull, called transcranial alternating current stimulation (tACS), to improve communication across different brain regions and improve memory performance in older adults .
Younger (ages 20-29) and older (ages 60-76) adults first wore a cap that measures the electrical activity in the brain. The researchers confirmed previous reports that the ability of different brain regions to communicate with one another is impaired in older adults. They also found that performance on a working memory task in older adults was slower and less accurate than younger adults. Working memory is a process of temporarily holding information in your mind, such as a telephone number.
Then the researchers tested whether tACS could improve the communication between different brain regions and improve memory. tACS is a procedure where electrodes are put on different parts of the head, in this case over two regions of the cerebral cortex called the left prefrontal cortex and left temporal cortex. Then weak currents are sent through the electrodes. After 25 minutes of tACS, those two brain regions communicated more effectively in older adults. In addition, accuracy on a working memory task improved. In fact, the older adults performed just as well as the young adults. However, performance on reaction time was more variable. These improvements lasted up to 50 minutes after the stimulation procedure stopped, which was the longest time measured. Importantly, the improvements depended on the electrodes being placed in the correct position.
There is a history of research testing whether other methods of brain stimulation, such as transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), can improve cognitive function in older adults or individuals with Alzheimer's disease. In tDCS, a weak, steady current is passed through electrodes on the skull. In TMS, a coil is placed over the head, and a magnetic field is used to stimulate the brain. Meta-analyses, or compilations of previous studies, suggest that tDCS and TMS may improve some aspects of cognition in older individuals and individuals with Alzheimer's disease . In some cases, these benefits remain well after the stimulation procedure is completed.
Although brain stimulation seems promising, it is still too early to stimulate your brain to improve cognition. Although tDCS and TMS are generally associated with few side effects, the most common being mild tingling or pain over the stimulation site, most of these studies were small and short. The side effects with many repeated stimulations are unknown. Additionally, there is a lot of variability in stimulation procedures across studies, and the best way to stimulate the brain is not currently known. In fact, an FDA advisory panel recommended that the best studied TMS protocol should not be approved for treating Alzheimer's, as it failed to improve cognitive function over a 6-week period. However, TMS is currently approved by the FDA for the treatment of depression, migraine, and obsessive-compulsive disorder.
Although brain stimulation techniques remain an interesting area of research for Alzheimer's and for improving cognition in elderly individuals, larger clinical trials with a validated protocol still need to be completed. In addition, all these studies were conducted in a laboratory setting, and it is still unknown whether a consumer brain stimulation device would improve cognition in older adults or those with Alzheimer's.
Nick McKeehan is Assistant Director, Aging and Alzheimer's Prevention at the Alzheimer’s Drug Discovery Foundation. He served as Chief Intern at Mid Atlantic Bio Angels (MABA) and was a research technician at Albert Einstein College of Medicine investigating repair capabilities of the brain. He received a bachelor of science degree in biology from Purdue University, where he was awarded a Howard Hughes Scholarship. Mr. McKeehan also writes about the biotechnology industry for 1st Pitch Life Science.
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