High-intensity stress elicits robust cortisol increases, and impairs working memory and visuo-spatial declarative memory in Special Forces candidates: A field experiment

Abstract

While running a selection procedure, 27 male Belgian Special Forces candidates, with a mean age of 27.4 years (SD = 5.1), were randomly assigned to a no-stress control (n = 14) or a high-intensity stress group (n = 13). Participants in the latter group were exposed to an extremely strenuous mock prisoner of war (POW) exercise. Immediately after stress or control treatment, working memory and visuo-spatial declarative memory performances were measured by the digit span (DS) test and the Rey–Osterrieth complex figure (ROCF), respectively. Concurrently, stress levels were assessed by obtaining salivary cortisol measurements and subjectively by the NASA Task Load Index (TLX). As expected, exposure to high-intensity stress led to both robust cortisol increases and significant differences in TLX scores. Stress induction also significantly impaired DS and ROCF performances. Moreover, delta cortisol increases and ROCF performance in the POW stress group showed a significant negative correlation, while DS performances followed the same tendency. Summarizing, the current findings complement and extend previous work on hormonal stress effects, and the subsequent performance deterioration on two memory tests in a unique high-intensity stress environment.

Keywords::

• Digit span test
• glucocorticoids
• high-intensity stress
• NASA TLX
• Rey–Osterrieth complex figure

Acknowledgements

The authors would like to express their sincere gratitude to the research team (Wouter Huybens, Ilse Provoost, Olivier Serniclaes, and Maarten Wendelen) for their valued assistance; to Jef Syroit, Susan van Hooren, and three anonymous experts for their appreciated comments on an earlier version of this article; and to the Belgian military authorities for their permission to conduct the research.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Notes

^† Morgan et al. (2006) applied the Taylor scoring system (TSS). For comparison purposes, as a (rough) guide, the TSS and the DnSS relate to each other as: TSS = 2/3 × DnSS. This relationship, however, is only indicative, given the deviating design approaches of both scoring systems (see Knight 2003a). Interested researchers are cordially invited to contact the first author to request copies of the current actual ROCF outcomes.