Like a young man, but not for long
Synchronization of brain activity has improved the working memory of the elderly
Elizaveta Ivtushok, N+1
American scientists have found that a decrease in the efficiency of working memory in old age occurs due to the loss of synchronization of the activity of some parts of the brain in the theta and gamma ranges (from 4 to 8 and over 25 Hertz, respectively). As reported in the article Reinhart & Nguyen Working memory revived in older adults by synchronizing rhythmic brain circuits, published in Nature Neuroscience, working memory can be restored using non-invasive direct current stimulation, which helps to adjust activity in the appropriate ranges again.
Some cognitive functions require increased connectivity between several parts of the brain. Such connectivity can be well tested by registering brain potentials – that is, electrical activity in a certain range. For example, during the use of working memory, the activity of the parietal zone in the gamma range (from 25 Hertz) is synchronized with the activity of the theta range (from 4 to 8 Hertz) so that the amplitude of gamma rhythms adjusts to the phase of theta rhythms, as well as the synchronization of theta rhythms during cognitive processes is observed between the temporal lobes and prefrontal cortex.
If such synchronization is key for cognitive processes, then it should be disrupted with age, accompanying the natural process of cognitive decline and neurodegeneration. Scientists led by Robert Reinhart from Boston University decided to check this, and also to see if it is possible to adjust activity using transcranial stimulation.
Their experiment involved 42 volunteers aged 20 to 25 years and 42 people aged 60 to 76 years. As the main task for working memory, the scientists showed the participants pictures for several milliseconds, after which, after a pause (from three seconds), they showed them again: the participants had to decide whether the new image was different from the one that had been shown before.
Behavioral data indicated that working memory performance does decrease with age (p < 0.001): the young evaluated the similarity of the images more correctly and faster than the older participants of the experiment. The participants' brain activity was recorded using EEG: the electrodes were located in the prefrontal cortex and temporal lobes. It turned out that the synchronization of theta and gamma rhythms in these areas when performing a task really decreases depending on age.
Next, the scientists decided to test how the participants' working memory would change when using transcranial direct current stimulation (micropolarization). It turned out that the working memory of older participants when using active stimulation became better and was comparable to the working memory of young participants in the experiment.
A drawing from an article in Nature Neuroscience – VM.
Since such an improvement was not observed with "empty" (sham) stimulation, scientists came to the conclusion that it is the restored synchronization of brain regions in the theta and gamma ranges that regulates the improvement of working memory in older people.
Scientists have thus shown that one of the biomarkers of cognitive decline in old age may be the loss of synchronization of brain activity in the prefrontal cortex and temporal lobes. This process, they note, is not irreversible: it is possible to restore lost functions with the help of brain stimulation, that is, maintaining artificial synchronization at the level that is observed in younger people. Despite the fact that the effect of the stimulation lasted for several minutes after its end, it still did not allow the researchers to restore the effectiveness of working memory to elderly participants in the long term – this, in their opinion, should be the focus of future research.
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