Effects Of Acute And Sustained Stress On Cognitive Performance During A 72-hour Military Training Mission

Stress can have varying impacts on cognitive function. Research shows that chronic, or sustained stress, may lead to declines in cognition, whereas acute stress may improve or impair performance depending on the cognitive domain assessed. However, research rarely examines the impacts of both acute and chronic stress on cognition within the same individual, or overlooks specialized cohorts (i.e. military personnel). Yet, Soldiers often experience varying forms and combinations of acute and sustained stressors during sustained operations (SUSOPS), i.e. encountering a firefight at the end of a multi-day mission. Thus, it is important to understand how varying aspects of cognitive function may change in response to acute and chronic stress experienced in operational environments. PURPOSE: To compare effects of acute and sustained stressors on cognitive performance over the course of a 72-hr military training exercise. METHODS: 62 active duty Soldiers (Age: 22.9 ± 3.2 yrs; 62 males), completed a series of cognitive tasks at Baseline (several weeks prior) and at three time points (T1, T2, T3) during a highly stressful 72-hr training mission. Soldiers performed Go/No-Go (GNG), N-back (NB), Task-Switching (TS), and Simple Reaction Time (SRT) tasks at T1, which occurred pre-mission following a live-fire exercise (acute stress); at T2, after approximately 36-hrs of mission activities (sustained stress); and at T3, after a second live-fire exercise at the end of the 72-hr mission (acute and sustained stress). RESULTS: Repeated Measures ANOVA’s showed main effects of Time for GNG and SRT tasks (p's < .05) Compared to Baseline, planned comparisons revealed that inhibition (GNG) declined following sustained stress, with false alarms increasing at T2 (p < .05); whereas reaction time (SRT) degraded following acute stress, with slower RTs at T1 (p < .01). GNG and SRT performance both declined due to the combined acute and sustained stress at T3 (p's < .01). Performance on TS and NB tasks remained unaffected. CONCLUSIONS: Acute and sustained stress experienced during SUSOPS differentially impacts cognition depending on the type of stress and cognitive domain assessed. These data show that effects of stress are nuanced and emphasize the importance of characterizing changes in cognition over multi-day missions. Funding: Army RDT&E