Abstract
There have been several studies of the neural mechanisms underlying sensation of fatigue. However, little is known about the neural mechanisms underlying self-evaluation of the level of fatigue. The aim of this study was to identify the neural substrates involved in self-evaluation of the level of mental fatigue. We used magnetoencephalography (MEG) with high temporal resolution on 14 healthy participants. During MEG recordings, participants were asked to evaluate their level of mental fatigue in time with execution cues (evaluation trials) or to do nothing in time with execution cues (control trials). The MEG data were analyzed with equivalent current dipole (ECD) and spatial filtering methods to localize the neural activity related to the evaluation of mental fatigue. The daily level of fatigue sensation was assessed using the Checklist Individual Strength questionnaire. In evaluation trials, ECDs were observed in the posterior cingulate cortex (PCC) in seven of 14 participants, with a mean latency of 366.0 ms. The proportion of the participants with ECDs in the PCC was higher in evaluation trials than in control trials (P<0.05, McNemar test). The extent of the decreased delta band power in the PCC (Brodmann’s area 31) 600–700 ms after the onset of the execution cue and that in the dorsolateral prefrontal cortex (DLPFC; Brodmann’s area 9) 800–900 ms after the onset of the execution cue were greater in the evaluation trials than in the control trials. The decrease in delta band power in the DLPFC was positively related to that in the PCC and to the daily level of fatigue sensation. These data suggest that the PCC and DLPFC are involved in the self-evaluation of mental fatigue.
Highlights
All the estimated equivalent current dipole (ECD) were located in the posterior cingulate cortex (PCC), except for these auditory responses to the execution cue observed within the time range of 0–200 ms
We examined whether ECDs can be estimated in the PCC when the participants evaluate their level of mental fatigue
We identified brain regions activated by self-evaluation of the level of mental fatigue by analyzing MEG data using ECD and spatial filtering methods
Summary
Over-estimation of the level of fatigue causes a severe fatigue sensation that can decrease physical and mental performance, resulting in further fatigue. An exaggerated fatigue sensation is thought to be involved in the pathophysiology of fatigue-related diseases such as chronic fatigue syndrome [8]. Under-estimation of the level of fatigue may cause overwork, which can be a cause of death in a working population, known as karoshi in Japan [9,10]. It is important to accurately evaluate the level of fatigue such that the intensity of the fatigue sensation matches the level of fatigue. Several studies have investigated the brain regions related to fatigue sensation [11,12,13,14], little is known about the neural mechanisms underlying self-evaluation of fatigue level
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