Neural effect of physical fatigue on mental fatigue: a magnetoencephalography study

Abstract

ABSTRACT Background: Mental fatigue manifests as a reduced efficiency of cognitive workload and has become a significant cause of accidents. It is important to clarify the neural relationships between physical fatigue and mental fatigue. Purpose: We sought to clarify the neural effect of physical fatigue on mental fatigue using magnetoencephalography (MEG), with high temporal resolution and relatively high spatial resolution and classical conditioning techniques. Methods: Fourteen right-handed volunteers participated in this study. On the first experimental day, participants performed fatigue-inducing mental task trials for 30 min. Metronome sounds, started just after the beginning of the trials, were used as conditioned stimuli and the mental task trials were used as unconditioned stimuli to induce mental fatigue. On the next day, MEG was recorded under an eyes-closed condition with the metronome sounds for 3 min just before (control session) and after a 10-min fatigue-inducing physical task session. Subjective fatigue and motivation were rated on visual analogue scales. Results: In the left caudate, decreased alpha-band power in the physical fatigue session relative to the control session was found. The magnitude of the reduced power was positively associated with subjective level of motivation during the fatigue-inducing physical task session. Conclusion: These results suggest that physical fatigue suppressed activity in the left caudate via increased motivation to compensate for the effects of fatigue.