Although it is said that with age comes wisdom, the harsh reality is that ageing also leads to a progressive deterioration of brain function. Certain aspects of perception, memory, and attention seem to be the most significantly affected, which can set the stage for dreadful accidents among older people. Luckily, various experimental protocols are being tested as potential ways to mitigate or even reverse age-related cognitive decline.
One such protocol is called transcranial direct current stimulation (tDCS). This non-invasive procedure involves using electrodes to circulate small electrical currents through specific parts of the brain, modulating neuronal activity. While many studies have reported that tDCS can improve the cognitive capabilities of older people, it has proven difficult to rigorously quantify and compare these improvements between studies because of the different methodologies and experimental paradigms used.
To help fill this knowledge gap, a team of scientists from Incheon National University in Korea, conducted a meta-analysis of previously published studies on tDCS as a technique to improve cognitive performance. Unlike existing meta-analyses, the researchers assessed the improvement produced by tDCS by comparing the changes in reaction time during various cognitive tasks. This essentially circumvented the problem posed by the large heterogeneity in the methodologies used for tDCS research. The research was published in the journal Ageing Research Reviews.
After searching for and filtering relevant tDCS studies, the team ended up with 31 qualifying papers involving 934 healthy adults. They categorised the studies based on the cognitive domains targeted by the tasks given to the subjects, such as perceptual–motor function, learning and memory, executive function, and language. Additionally, the researchers analysed if the timing of the tDCS was relevant; that is, if applying tDCS before or during the tasks had different effects in reaction time.
The results of the statistical analyses conducted by the team indicate that applying tDCS during the tasks produced a small yet significant improvement in reaction times, specifically in learning and memory tasks and executive function/complex attention tasks. This improvement was more pronounced in older people, suggesting the positive effects derived from tDCS increase with age. ‘Our meta-analysis extends prior findings that suggested tDCS protocols could improve cognitive functions and effectively increase cognition-related neural processing speed,’ remarks associate professor Nyeonju Kang, who led the study.
Overall, this study highlights tDCS as an effective therapeutic option for improving the lives of older people. ‘If we prove tDCS protocols effectively enhance cognitive functions, home-based tDCS programmes could be developed to prevent the progression of age-related cognitive deficits, thereby increasing life satisfaction among the elderly population,’ concludes Dr Kang.