Evaluating Autonomic and Cognitive Responses to Transcranial Direct Current Stimulation as a Countermeasure for Sleep Deprivation

Background/Objectives: Acute sleep deprivation impairs cognitive performance in safety-critical occupations, highlighting a demand for effective countermeasures. Transcranial direct current stimulation (tDCS) has been explored as an alternative noninvasive neuromodulatory approach to mitigating performance decline. Groups have also capitalized on the ability of biosignals like heart rate variability (HRV) to continuously track performance decline during extended wakefulness, but whether fatigue interventions like tDCS shift the autonomic measures used in such tracking during sleep deprivation remains unknown. This study examined whether tDCS affects autonomic function and cognitive performance during sleep deprivation. Methods: Nineteen participants underwent 26 h of continuous wakefulness with repeated cognitive assessments and electrocardiogram monitoring. After 19 h awake, participants received 30 min of verum (n = 10) or sham (n = 9) tDCS targeting the right dorsolateral prefrontal cortex in a double-blind design. Performance and HRV were analyzed with linear mixed-effects models with false discovery rate correction, including 5 min windowed analyses of the Multi-Attribute Task Battery-II (MATB). Results: Stimulation had no significant main effect on any cognitive performance or HRV outcome. Exploratory analyses revealed stimulation × window interactions within the MATB for system monitoring reaction time, resource management performance, and absolute high-frequency HRV power. Verum participants reported lower sleepiness at a single post-stimulation round without a corresponding performance benefit. Conclusions: In this exploratory sample, a single tDCS session produced no detectable group-level effects on cognitive performance or HRV, and apart from one exploratory within-task interaction, no systematic stimulation-related shift in autonomic measures was observed. Effect size estimates and exploratory findings within tasks provide a basis for adequately powered studies examining individual variability in tDCS response.