Cognitive function and mood during acute cold stress after extended military training and recovery.

INTRODUCTION: Acute cold stress is often accompanied by exposure to other adverse factors, such as sleep loss, under-nutrition, and psychological stress that singly and together may affect cognitive function.

METHODS: The effect of moderate cold stress on cognitive function was investigated in 15 male volunteers exposed to cold air (10 degrees C) for 4 h after they had completed an intense, 61-d regimen (U.S. Army Ranger training). The single cohort of volunteers was tested on three separate occasions: (1) immediately after completing Ranger training; (2) 2 d later when they had partially recovered from training; (3) 108 d later after full recovery. Documented training stressors included limited sleep (approximately 4 h sleep/night), caloric deficit (approximately 850 kcal x d(-1), intense physical activity, and psychological stress.

RESULTS: Baseline rectal temperature fell significantly due to training alone (from 36.6 degrees C +/- 0.1 to 36.3 degrees C +/- 0.1) and was lower still with acute cold exposure (35.9 degrees C +/- 0.2). Cognitive function was affected by training alone, as indicated by significant decreases in vigilance, four-choice reaction time, pattern recognition, symbol-digit substitution, word-list learning, grammatical reasoning, and mood prior to exposure to acute cold stress. Mood states were also adversely affected, including tension, depression, anger, fatigue, confusion, and vigor. Acute cold exposure itself significantly degraded vigilance, overall mood, and increased tension.

DISCUSSION: Chronic multifactorial stress impaired cognitive function and mood; the addition of moderate, acute cold stress further degraded vigilance and mood. When such circumstances occur, such as during disasters or military operations, measures to prevent adverse cognitive and physiological outcomes are recommended.