Attempting to counteract vigilance decrement in older adults with brain stimulation

Löffler, Birte S.; Stecher, Heiko I.; Meiser, Arnd; Fudickar, Sebastian; Hein, Andreas; Herrmann, Christoph S. · 2023 · Crossref

DOI: 10.3389/fnrgo.2023.1201702

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Summary

This study investigated whether 40-Hz transcranial alternating current stimulation (tACS) could counteract vigilance decrement in older adults, a phenomenon characterized by slowing reaction times and rising occipital alpha power during sustained attention tasks. Motivated by demographic shifts toward an aging society and prior success in young adults, the researchers aimed to determine if gamma-tACS, which downregulates alpha power via cross-frequency coupling, would similarly enhance vigilance in participants aged 65 and older. The study employed a single-blind, randomized controlled design with 49 independent-living older adults (mean age 72.4 years), who were assigned to one of three groups: 40-Hz tACS, 5-Hz tACS, or sham stimulation. Participants completed two 30-minute blocks of a visual sustained attention task, with stimulation applied only during the second (intervention) block. EEG data were recorded before and after each block to monitor alpha power, while reaction times and error rates were tracked throughout. Statistical analysis using linear mixed models revealed that reaction times increased significantly over time in the baseline block for all groups, with no significant differences between the sham, 5-Hz, and 40-Hz groups. In the intervention block, the rate of reaction time increase was not significantly different among the groups when using the 5-Hz or 40-Hz groups as the baseline for comparison, contrary to the hypothesis that 40-Hz stimulation would flatten the slope of vigilance decrement. Specifically, the 40-Hz group showed a slightly steeper increase in reaction times (3 ms/min) compared to the sham and 5-Hz groups (1 ms/min each), though these differences did not reach statistical significance. Generalized linear mixed model analysis of EEG data showed that alpha power was significantly higher after the experiment (1.37 µV²) than before (1.00 µV²), but no significant influence of stimulation frequency (40 Hz, 5 Hz, or sham) on alpha power was detected. The findings indicate that the specific 40-Hz tACS protocol effective in young adults did not successfully counteract vigilance decrement or downregulate alpha power in this older cohort. The authors conclude that results from general or younger populations cannot be directly transferred to older adults due to age-related neurophysiological changes. They suggest that future studies should adjust stimulation parameters to account for the specific neural characteristics of aging brains, while also considering factors such as individual heterogeneity, cognitive fitness, motivation, and medication use. This highlights the need for tailored neuroenhancement strategies for older adults to support their participation in society and quality of life.

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• neuro workload indices