Modulation of Metabolic Rate in Response to a Simple Cognitive Task

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Abstract
Aim: The effect of cognitive activity on human metabolic rate is incompletely understood. To investigate changes in human metabolism during periods of cognitive demand, we measured the effect of simple cognitive activity on energy expenditure during a cognitive task. Methods: Nine healthy volunteers participated in a simple cognitive-motor task with both response priming and neutral (non-response priming) conditions, enabling assessment of cognitive interference. Energy expenditure was measured during repeated alternating test and rest phases, lasting approximately 2 minutes each. Results: Energy expenditure (EE) was significantly greater during test than during rest phases (mean EE=29.1 kcal/kg/d, SE=1.24 vs 25.1 kcal/kg/d, SE=1.19), F(3, 18)=8.18, p=0.029. Following each test phase, energy expenditure initially continued to rise (‘rebound spike’) before dropping rapidly. Rebound spikes showed significantly larger peaks following priming than following neutral cognitive-motor test phases. Conclusion: We demonstrate for the first time that overall energy expenditure is influenced by simple cognitivemotor tasks in healthy human participants. We provide proof of concept that indirect calorimetry is a sufficiently sensitive measure to detect even subtle difference in cognitive demands (interference versus non-interference) between tasks with identical response demands (speeded left and right key-presses).