Military training and operations can place significant demands on cognitive and physical resources of service members, resulting in heightened stress and fatigue, elevated risk of accidents and injuries, and diminished cognitive and occupational performance. Transcutaneous electrical stimulation (TES) is a novel, non-invasive neuromodulatory technique being investigated as a means to improve alertness and preserve performance under stress with few-to-no side effects. Despite the recent increase in research using TES, few studies have explored the effects of stimulation of the trigeminal nerve on cognition and the human stress response. Therefore, the aims of this study were to elucidate the effects of TES on biochemical and physiological responses to stress, cognition, and marksmanship performance under cognitive load.
Participants in this repeated measures, crossover-design study included 23 healthy male (n = 18) and female (n = 5) civilians and members of the military ranging in age from 19 to 37 (mean 24.00 ± 5.65) years. Study procedures occurred in the afternoon on five consecutive days, including two testing days involving administration of active or sham TES to the right supraorbital region of the face using a commercially-available device (Thync One, Cerevast Therapeutics). To evaluate the effects of TES on the stress response, participants were required to complete a prolonged, cognitively challenging target discrimination task using a simulated firing range, which has been previously demonstrated to induce a reliable stress response in human research volunteers. Computer-assisted cognitive tasks were administered before and after rifle marksmanship in order to provide complementary assessment of functional domains challenged during the marksmanship task. Salivary markers of cortisol and α-amylase were collected at several time points during the testing day, and electrocardiography (ECG) and photoplethysmography (PPG), both markers of heart rate variability and stress responding, were monitored continuously. Linear mixed models with random slopes were used to analyze the effect of stimulation condition (active versus sham TES) on marksmanship and cognitive, physiological, and salivary outcomes across the testing period and at each measurement time point.
No significant effects of stimulation condition or the interactions between stimulation condition and measurement time point were found for salivary stress biomarkers (punadj range 0.12 – 0.98) or for cognitive (punadj range 0.25 – 0.88) and physical workload (punadj range 0.31 – 0.79). There were no significant effects of stimulation condition on time-series indicators of heart rate variability (punadj range 0.10 – 0.96) except for pNN50 when measured with PPG (β = -4.97, punadj = 0.04, padj = n.s., d < 0.01). There were, however, significant stimulation condition by time interaction effects on mean heart rate, mean R-R interval, SDNN, RMSSD, and pNN50 (punadj range 0.12 – 0.98, d range < 0.01 – 0.02), indicating that trigeminal TES using the Thync One device increased activity of both the sympathetic and parasympathetic nervous systems during marksmanship and cognitive testing. Similar effects were noted on frequency-series indicators of heart rate variability using both ECG and PPG, in which stimulation condition effects were noted on ECG high frequency absolute (β = 8.50, punadj < 0.01, padj = 0.01, d < 0.01) and relative powers (β = -8.54, punadj < 0.01, padj = 0.01, d < 0.01), as well as PPG very low frequency power (β = -367.98, punadj < 0.01, padj = n.s., d = 0.12). Effects of the interaction between stimulation condition and measurement time point were noted on very low, low, and high frequency powers (punadj range < 0.01 – 0.048, d range < 0.01 – 0.21), as well as the ratio of low- to high-frequency powers in ECG (punadj range < 0.01 – 0.048, d < 0.01 for all). These results also suggest that trigeminal TES increased activity of both the sympathetic and parasympathetic nervous systems during marksmanship and cognitive testing.
Furthermore, significant effects of stimulation condition were noted on marksmanship shot accuracy (β = 0.14, punadj = 0.01, padj = n.s., d = 0.60) and distance of shots from the targets’ center of mass (β = -0.08, punadj = 0.02, padj = n.s., d = 0.56), indicating that trigeminal TES impaired shot accuracy. There were also significant condition-by-time interaction effects on target detection latency (β = 220.46, punadj = 0.04, padj = n.s., d = 0.49); significant impairments in shot latency observed during the first marksmanship session in the active TES condition only resolved by the second marksmanship session. There were no significant effects of TES on accuracy or response times for neuropsychological tasks assessing response inhibition, sustained attention, and working memory (punadj range 0.09 – 0.98). Active trigeminal TES did, however, significantly reduce the standard deviation of response times on a measure of sustained attention and response inhibition (β = -16.29, punadj = 0.045, padj = n.s., d = 0.43).
Although the literature suggests that TES may benefit stress and performance, these results do not support that conclusion. Overall, these analyses found that TES using a commercially available device did not influence chemical biomarkers of stress, but did influence markers of physiological stress, as well as cognitive and marksmanship performance under high cognitive load. TES was associated with impairments in marksmanship performance as well as increases in both sympathetic and parasympathetic nervous system activity. Further studies using different stimulation parameters, including multiple sessions of stimulation, will be necessary to more fully characterize possible influences of trigeminal nerve stimulation on stress responding and marksmanship performance or other military relevant tasks. In addition, this project underscores the need for more investigation into the mechanisms of effect of the Thync One device and other devices applying TES of the trigeminal nerve.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45517 |
| Date | 24 January 2023 |
| Creators | Ridgewell, Caitlin Rael |
| Contributors | Rasmusson, Ann M., Heaton, Kristin J. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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