Individual Differences in Biophysiological Toughness: Sustaining Working Memory During Physical Exhaustion

Abstract

Recent evidence suggests that increased dehydroepiandrosterone sulfate (DHEAS), in combination with decreased cortisol levels have been correlated with enhanced performance outcomes in stressful military environments. This study was implemented to replicate these findings in a group of active duty Air Force members to provide information on the usefulness of these biomarkers indices in the training and operational environment. Seventeen active duty males participated in the 4 sessions of this study. Sessions 1 and 2 were training days for the cognitive testing. Session 3 was a baseline measure of physical fitness, utilizing the VO2 Maximal Treadmill test. Session 4 was centered around a modified-Astrand treadmill protocol designed to induce physical exhaustion. Blood draws for biomarker analysis, cognitive testing (NovaScan), psychomotor vigilance, and physiological measures were collected before, during, and following the treadmill protocol. Results showed that prolonged increases in cortisol negatively correlate with working memory performance. DHEAS release from baseline to poststress was negatively related to the changes in cortisol for 20 minutes following stress. These results indicate that the ratio of DHEAS to cortisol buffers, the effect of cortisol increases that are related to poor working memory performance because of physical exhaustion.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders

“…DHEA and DHEAS appear to counteract the negative effects of increased cortisol on working memory function in women and men, respectively (315, 316). A dose-dependent inverted U-shaped response to DHEAS is observed on tests of learning and memory function in male mice (30).…”

Physiological Factors Which Influence Cognitive Performance in Military Personnel

“…In a recent meta-analysis, acute physical activity was reported to improve cognition when intensity is light to moderate, but when the activity is reported as hard to maximal, no benefit is observed (Chang, Labban, Gapin, & Etnier, 2012). Working memory accuracy was facilitated by physical exertion for the first 21 min of an incremental treadmill protocol, after which there was no difference to baseline (Shia et al, 2015). Pre to post the treadmill protocol, reaction time on a vigilance task was 6% slower (Shia et al, 2015), as well as 7% slower following a 2-hr treadmill march (Eddy et al, 2015).…”

“…Working memory accuracy was facilitated by physical exertion for the first 21 min of an incremental treadmill protocol, after which there was no difference to baseline (Shia et al, 2015). Pre to post the treadmill protocol, reaction time on a vigilance task was 6% slower (Shia et al, 2015), as well as 7% slower following a 2-hr treadmill march (Eddy et al, 2015). Following a 6.5-hr treadmill march, working memory accuracy was 7% worse and sensitivity on a vigilance task, calculated as z (hit rate) – z (false alarm rate), was ~20% lower (Bonnet, 1980).…”

Cognitive, Psychophysiological, and Perceptual Responses to a Repeated Military-Specific Load Carriage Treadmill Simulation

“…The same research group observed similar HRV relationships in naval cadets, but also demonstrated an association between cortisol levels and cognitive performance (Johnsen et al, 2012). In a study by Shia et al (2015), prolonged cortisol responses were also negatively associated with working memory, with DHEA-S:cortisol ratio demonstrating the potential to indicate resilient individuals. Whilst caveats to the research exist (e.g., dichotomous HRV groupings), collectively these biomarkers demonstrate potential.…”