External trigeminal nerve stimulation (eTNS) Exhibits relaxation effects in fatigue states following napping deprivation

Abstract

Background

In the face of inevitable declines in alertness and fatigue resulting from sleep deprivation, effective countermeasures are essential for maintaining performance. External trigeminal nerve stimulation (eTNS) presents a potential avenue for regulating alertness by activating the locus coeruleus and reticular activating system.

Methods

Here, we conducted a within-subject study with 66 habitual nappers, subjecting them to afternoon nap-deprivation and applying either 20-minute of 120 Hz eTNS or sham stimulation. We compared participants’ performance in PVT and N-back tasks, subjective fatigue level and alertness ratings, and changes in heart rate variability, cortisol, and salivary alpha-amylase before and after stimulation.

Results

The results revealed a significant decline in PVT and N-back tasks performance, along with increased subjective fatigue levels in the sham stimulation group. In contrast, the eTNS stimulation group maintained behavioral performance, with lower post-stimulation fatigue levels than sham group. After stimulation, the eTNS group exhibited decreased mean R-R interval and elevated LF/HF ratios, i.e., a shift in autonomic nervous system activity towards sympathetic dominance, and a significant reduction in cortisol levels, indicating a state of relaxation alleviating drowsiness.

Conclusion

These findings suggested that 120 Hz eTNS stimulation might induce a relaxing effect, and thereby alleviate fatigue while preserving alertness and cognitive performance.