Anodal tDCS improves attentional control in older adults

Hanley, Claire J.; Tales, Andrea · 2019 · Crossref

DOI: 10.1016/j.exger.2018.11.019

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Summary

This study investigates whether transcranial direct current stimulation (tDCS) can enhance attentional control in older adults, a cognitive domain often neglected in prior research despite significant age-related declines. The authors address a gap in the literature where previous tDCS protocols failed to account for age-associated structural brain changes, such as increased cerebrospinal fluid volume and cortical atrophy, which alter current distribution. Consequently, the study aimed to develop and test an age-optimised stimulation protocol tailored to the physiological characteristics of the ageing brain. The researchers employed a double-blind, randomized design involving 24 older adults (mean age 66.5 years), who were assigned to either an active anodal tDCS group or a sham control group. Participants underwent three sessions of stimulation spaced 48 hours apart. The stimulation protocol targeted the dorsolateral prefrontal cortex (dlPFC) using a bihemispheric electrode configuration (anode at F3, cathode at F4) with a current intensity of 1.5 mA for 20 minutes, parameters selected to compensate for age-related current shunting. Cognitive performance was assessed using the Swansea Test of Attentional Control (STAC), a novel task switching paradigm that combines selective attention, task monitoring, and response inhibition. The task utilized a dynamic algorithm to adjust stimulus speed based on participant accuracy, ensuring appropriate difficulty levels. The results demonstrated that anodal tDCS significantly improved attentional control, specifically in terms of processing speed. While there were no significant differences in baseline performance or accuracy between groups, the anodal group exhibited a substantial increase in task switching speed following the third stimulation session compared to baseline (p < .01, Cohen’s d = 1.36). This improvement was unique to the active stimulation group, as the sham group showed no comparable gains despite identical task exposure. The effect was acute and post-stimulation, emerging only after repeated applications rather than immediately after the first session. No significant differences in accuracy were observed between groups. The findings provide the first evidence that tDCS protocols specifically tailored for older adults can effectively modulate attentional control. The study highlights that age-optimised parameters, such as increased current intensity and duration, are necessary to overcome physiological barriers in the ageing brain. These results suggest that non-invasive brain stimulation is a viable intervention for enhancing executive function in later life, with potential implications for maintaining cognitive health, independence, and daily functioning in an ageing population.

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• executive function