Combat Stress: What is the Effect on Cognitive Performance & Mood?

Members of the Sea Air Land Team Five (SEAL5),...
Members of SEAL Team (photo credit: Wikipedia)

Research Paper Title

The Fog of War: Decrements in Cognitive Performance and Mood Associated with Combat-like Stress.


Anecdotal reports from military conflicts suggest cognitive performance and mood are severely degraded by the stress of combat. However, little objective information is available to confirm these observations.


The researchers laboratory had several unique opportunities to study cognitive function in warfighters engaged in exercises designed to simulate the stress of combat. These studies were conducted in different environments with two different types of military volunteers. In one study, subjects were officers, with an average 9 years of military service, who were members of an elite US Army unit, the Rangers. In the other study, participants were younger, mostly enlisted, trainees with only 3 years of military experience on average, in training to determine if they would qualify for an elite US Navy unit, the SEALS. The researchers administered a variety of identical, computer-based cognitive tests to both groups.


In both groups, during stressful combat-like training, every aspect of cognitive function assessed was severely degraded compared with baseline, pre-stress performance. Relatively simple cognitive functions such as reaction time and vigilance were significantly impaired, as were more complex functions, including memory and logical reasoning.


The deficits observed were greater than those typically produced by alcohol intoxication, treatment with sedating drugs, or clinical hypoglycemia. Undoubtedly, such decrements would severely degrade operational effectiveness. Furthermore, it is likely such cognitive decrements would be greater during actual combat. War planners, doctrine developers, and warfighters, especially leaders, need to be aware that combat stress will result in extensive and severe deficits in cognitive performance.


Lieberman, H.R., Bathalon, G.P., Falco, C.M., Morgan, C.A., Niro, P.J. & Tharion, W.J. (2005) The Fog of War: Decrements in Cognitive Performance and Mood Associated with Combat-like Stress. Aviation, Space and Environmental Medicine. 76(7 Suppl), pp.C7-14.


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