A systematic review on the effects of tACS on cognitive function within older adults

Abstract

AbstractBackgroundNovel interventions that delay the onset or delay the progression of cognitive decline in older adults are extremely important, especially as the proportion of older adults steadily grows. Data on transcranial Alternating Current Stimulation (tACS) suggests it may have the potential for improving cognitive function; however, the direct implication for older adults, including those with cognitive impairment is far less understood. It is imperative to better understand the effects of tACS on cognitive function within older adults, along with treatment parameters if the therapeutic utility of tACS is to be realized.MethodFor this reason, we performed a systematic review of the literature to evaluate the effectiveness of tACS on cognitive functions within older adults. Databases were reviewed up to February 2022, which initially produced 347 unique projects. Thirty‐seven articles passed initial screening eligibility and the full texts were reviewed. Eligibility criteria included single and multiple session frequency‐specific tACS applied with the purpose of modulating cognitive performance in one or multiple cognitive domains in older adults. A total of 14 reports met the eligibility criteria and were included in the review, consisting of 294 older adults receiving tACS.ResultThe systematic review revealed that tACS show improvement in cognitive function for cognitively intact older adults (n = 5), those with mild cognitive impairment (n = 3), multi‐etiological dementia (n = 3), and Parkinson’s (n = 2), whereas 2 Alzheimer’s reports and 1 healthy aging report found no improvements. Gamma (n = 7) and Theta (n = 6) frequencies were largely targeted and showed modulations in memory, executive functioning, working memory, and gross cognitive screening measures.ConclusionDiscussion will focus on the impact of various stimulation parameters and experimental methods since significant heterogeneity in these factors indicates the need for greater standardization. In summary, tACS appears beneficial across the ADRD continuum but the intentional mapping of parameter space and standardized outcomes will be vital for future translational efforts.