New Delhi: A new study conducted by US researchers has found that non-invasive electrical brain stimulation performed on an aging person can lead to improvements in their working and long-term memory.
Whether it can help senior citizens retain their everyday memories is yet to be ascertained, but evidence suggests they might be able to at least remember their grocery lists with more ease.
The study shows that this applies to adults over the age of 65 and that the improvement in their brain function lasts for at least a month.
The findings, which have been peer-reviewed, were published on 22 August in the journal Nature Neuroscience.
The randomised double-blind study was conducted by Robert M.G. Reinhart, director of the Cognitive and Clinical Neuroscience Laboratory at Boston University, Massachusetts, and assistant professor in the university’s department of psychological and brain sciences, with his associates.
Conducted on senior citizens between the ages of 65 and 88, the study involved the researchers applying oscillating electrical currents of different frequencies to specific areas of the brain via electrodes on the scalp — a process called transcranial alternating current stimulation, or tACS.
The research consisted of two experiments done with 60 participants in each and a third with 30 participants.
The weak electrical currents were applied repeatedly to the subjects, who were given a list of 20 words they needed to remember, over four consecutive days. They noticed that memory improvements in these individuals persisted a month after intervention.
“Whether these improvements would occur for everyday memories, rather than just for lists of words, remains to be tested,” said Masud Husain, a professor of neurology and cognitive neuroscience at the University of Oxford in a statement. He was not involved in the study.
According to the study, “Previous research has characterised a capacity-limited working memory (WM) store for brief maintenance of information and an unlimited long-term memory (LTM) store for sustained maintenance of information.”
Thus, if the unique rhythmic mechanisms in these regions are identifiable, then these brain rhythms can be independently manipulated using various techniques, such as “high-definition transcranial alternating current stimulation”, in order to improve memory performance.
Using this, the team demonstrated that the ‘inferior parietal lobe’, located towards the back of the brain and associated with visuospatial processing, or the ability to tell where objects are in space, enhanced working memory when stimulated with moderate electrical current.
It was also found that improving long-term memory depended on stimulating the ‘dorsolateral prefrontal cortex’, a region located close to the front part of the brain associated with language processing.
“Based on the spatial location and the frequency of the electrical stimulation, we can improve either short-term memory or long-term memory separately,” a news report quoted Reinhart as saying. He added that this means researchers “can tailor the treatment to a person’s needs” or according to “desired results”.
The team that conducted this study continues to look at whether tACS can help people with conditions such Alzheimer’s disease since the study indicated that brain stimulation might provide the greatest benefits to those who have poor cognitive function and memory in the first place.
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The process
In the first experiment, 60 participants were randomly assigned to one of three groups — the first group received high-frequency waves in their dorsolateral prefrontal cortex, the second low-frequency waves in their inferior parietal lobe and the third was a control group.
After receiving stimulation, each participant was asked to recall a list of 20 words given to them before the experiment. The entire process lasted 20 minutes.
Researchers found that longer-term memory, or the ability to recall words from the beginning of the test, improved in 17 of the 20 participants who received ‘high-frequency gamma stimulation’.
Similarly, in 18 of 20 participants who underwent ‘lower-frequency theta stimulation’, an improvement in short-term working memory was noted, meaning they remembered words towards the end of the list better.
Compared with the control group of people receiving the sham or placebo stimulation, those who received the treatments saw results that “translate to the older individuals recalling, on average, four to six words more out of the list of 20 words by the end of the four-day intervention,” said Reinhart.
In the second experiment, the researchers switched the frequency between the two parts of the brain which were being stimulated, but that showed no major results.
A third experiment was done to verify the previous results. This one resembled the first experiment but with only 30 participants receiving the stimulation for three days and no control group.
Understanding brain waves
Brain waves are essentially a form of electrical activity emanating from the brain.
There are mainly five types of brain waves with varying frequencies and amplitudes — alpha, beta, theta, delta and gamma. The two brain waves applied in the study were theta and gamma, of which theta is typically of greater amplitude, slower frequency, and is associated with relaxation. On the other hand, the gamma brain waves are the fastest and are associated with being highly alert and conscious.
The research team hypothesised that the long-lasting memory can be explained by a mechanism known as ‘entrainment’, in which brain waves spontaneously synchronise to outside stimuli, like music or flickering lights.
Shrey Grover, a PhD student in Reinhart’s lab and the study’s first author, has said that “the consequence of modifying the timings at which brain cells activate is that it initiates this process of plasticity.”
The term “neuroplasticity” refers to how the strength of the connections between our neurons constantly changes in response to brain activity.
Overall, the study revealed that low-frequency theta stimulation at 4 Hz improves short-term working memory, and high-frequency gamma stimulation at 60 Hz improves long-term memory.
The study also found that those who had the poorest memory capabilities initially, displayed the best and most rapid improvements in their memory enhancements a month later.
(Edited by Zinnia Ray Chaudhuri)
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