Cognitive load-dependent effects of HD-tDCS on the executive vigilance decrement: insights from aperiodic EEG activity.

Hemmerich, K; Lupiáñez, J; Martín-Arévalo, E; Cohen Kadosh, R · 2025 · PubMed Central

DOI: 10.3389/fcogn.2025.1677285

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Summary

This study investigates whether high-definition transcranial direct current stimulation (HD-tDCS) can mitigate the executive vigilance (EV) decrement—a decline in the ability to detect rare, critical stimuli over time—and how this effect depends on cognitive load. The research specifically examines the role of aperiodic electroencephalography (EEG) markers, namely the aperiodic exponent and offset, as mechanistic indicators of cortical excitation/inhibition (E/I) balance. Motivated by inconsistent findings in prior tDCS research, the authors sought to determine if stimulation efficacy varies with task demand and whether changes in spectral dynamics explain behavioral outcomes. The study employed a between-participant design with 180 healthy adults (aged 18–35) divided into anodal HD-tDCS (n=90) and sham (n=90) groups. Participants performed one of three versions of the ANTI-Vea task to manipulate cognitive load: single-task (low demand), dual-task, or triple-task (high demand). Anodal HD-tDCS was applied over the right posterior parietal cortex (rPPC) during the middle blocks of the task. EEG was recorded from six electrodes before and after stimulation. Power spectra were parametrized using the FOOOF algorithm to extract aperiodic components (exponent and offset) across two frequency ranges (1–35 Hz and 30–45 Hz), allowing for the separation of non-oscillatory activity from periodic oscillations. Results indicated that HD-tDCS reduced the aperiodic exponent in the 30–45 Hz range, reflecting a flattening of the spectral slope consistent with increased cortical excitation. This neural change was associated with a mitigated EV decrement under high cognitive load (triple-task) but an exacerbated decrement under low demand (single-task). These findings suggest a mechanistic link between shifts in E/I balance and behavioral performance. However, the effects reached significance only under directional hypotheses and appeared obscured by a push-pull relationship with the aperiodic offset, indicating complex interactions between local excitability and broadband spectral dynamics. Baseline aperiodic markers did not moderate the stimulation effect but predicted overall task performance independently of stimulation. The study concludes that HD-tDCS effects on vigilance are state-dependent, varying significantly with cognitive load and underlying spectral dynamics. By demonstrating that aperiodic EEG features modulate stimulation outcomes, the findings underscore the importance of considering endogenous neural states when designing brain stimulation protocols. The results highlight the need for refined, state-sensitive approaches to mitigate vigilance decrements, suggesting that uniform stimulation protocols may not be effective across different cognitive demands.

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• sustained attention vigilance

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• Empirical Findings: physiological data