Preserving Early Neurovascular Responses: The Effect of tACS on the Hemodynamics in Stressed Individuals.

This study examines the impact of transcranial alternating current stimulation (tACS) on the initial dip; an initial decrease in oxygenated hemoglobin (HbO) that arises during early neural activation, in individuals experiencing mental stress. Using functional near-infrared spectroscopy (fNIRS), we examined the effects of tACS on the initial dip and prefrontal activation in 40 participants subjected to mental stress induced by the Stroop Color-Word Task. The results indicate that tACS maintains the amplitude of the initial dip following stimulation, showing no significant change in amplitude ( ${p} \gt 0.05$ ). In contrast, the sham group demonstrated a significant increase in initial dip amplitude ( ${p} \lt 0.05$ ). This indicates that tACS improves neural efficiency by sustaining initial metabolic responses. Moreover, tACS-induced changes in functional connectivity demonstrated a reorganization of brain activity, characterized by a significant reduction in task-based connectivity ( ${p} \lt 0.001$ ), which may enhance cognitive performance. Behavioral and physiological measures indicated a 15% reduction in salivary alpha amylase levels and a 20% improvement in NASA Task Load Index scores, thereby supporting the stress-mitigating effects of tACS. Machine learning classifiers demonstrated significant accuracy in differentiating brain states, achieving classification accuracies as high as 92.6% for the initial dip phase utilizing convolutional neural network. The findings underscore the therapeutic potential of tACS in modulating early neural responses to stress, providing new insights into non-invasive modulation for cognitive performance and mental well-being.