Influence of transcutaneous electrical stimulation on marksmanship, cognition, and the healthy stress response

Transcutaneous electrical stimulation of the trigeminal and cervical nerves (TEN) has been proposed as a safe, noninvasive method of reducing stress. However, its effects on human performance and stress physiology have yet to be explored. This study explored the effects of TEN on physiological responses to stress and cognitive performance using both laboratory-standard tests of executive function and attention and a complex marksmanship task requiring sustained discrimination of friend or foe targets. Thirty healthy male and female participants completed two, single-blinded experimental sessions in which TEN or sham (order counterbalanced, n = 15 each group) was administered for 20 min prior to marksmanship and cognitive assessment. Heart rate variability was monitored continuously via electrocardiography and photoplethysmography while salivary markers of stress (cortisol, α-amylase) were collected at regular intervals. Linear mixed model analyses with standardized regression coefficients (β_stan) and 95 % confidence intervals (CI) indicated no effects of stimulation condition (TEN versus sham) on marksmanship performance, cognition, salivary cortisol, or α-amylase. However, significant effects of stimulation condition were observed on heart rate variability, including increased photoplethysmography mean heart rate (β_stan = -0.42 (95 % CI -0.69 - -0.14), p = 0.04) and decreased very low frequency power (β_stan = 1.51 (95 % CI 0.53-2.49), p = 0.04) during marksmanship and increased electrocardiography high-frequency power at rest (β_stan = -0.63 (95 % CI -1.06 - -0.21), p = 0.05). These results suggest that TEN may modulate the stress response via paradoxical effects on both sympathetic and parasympathetic nervous system activity.