Abstract
Fatigue reflects the functioning of our physiological negative feedback system, which prevents us from overworking. When fatigued, however, we often try to suppress this system in an effort to compensate for the resulting deterioration in performance. Previous studies have suggested that the effect of fatigue on neurovascular demand may be influenced by this compensatory effort. The primary goal of the present study was to isolate the effect of compensatory effort on neurovascular demand. Healthy male volunteers participated in a series of visual and auditory divided attention tasks that steadily increased fatigue levels for 2 hours. Functional magnetic resonance imaging scans were performed during the first and last quarter of the study (Pre and Post sessions, respectively). Tasks with low and high attentional load (Low and High conditions, respectively) were administrated in alternating blocks. We assumed that compensatory effort would be greater under the High-attentional-load condition compared with the Low-load condition. The difference was assessed during the two sessions. The effect of compensatory effort on neurovascular demand was evaluated by examining the interaction between load (High vs. Low) and time (Pre vs. Post). Significant fatigue-induced deactivation (i.e., Pre>Post) was observed in the frontal, temporal, occipital, and parietal cortices, in the cerebellum, and in the midbrain in both the High and Low conditions. The interaction was significantly greater in the High than in the Low condition in the midbrain. Neither significant fatigue-induced activation (i.e., Pre<Post), nor its interaction with factor Load, was identified. The observed midbrain deactivation ([PreH – PostH]>[PreE– PostE]) may reflect suppression of the negative feedback system that normally triggers recuperative rest to maintain homeostasis.
Highlights
Fatigue is a physiological indication of the need for recuperative rest
The consequence was a rise in karoshi, which reached a record high of,150 cases per year during 2002–2008 [4]. In this functional magnetic resonance imaging study, we examined the neural correlates of compensatory effort under mental fatigue
Seven participants whose mean accuracy across the Pre session was less than 75% were excluded based on the assumption that they were already fatigued or were unaccustomed to the functional magnetic resonance imaging (fMRI) environment
Summary
Fatigue is a physiological indication of the need for recuperative rest It is the response of a normally functioning negative feedback system that aims to protect the body and the brain from damage due to overload. It is often advantageous or necessary to suppress the negative feedback system at the expense of comfort, and to the cost of overworking ourselves in a competitive world, in order to rise above others in work performance or even just to achieve mediocrity. This compensatory effort may, when overexerted, lead to indefinite sick leave for organ dysfunction. The consequence was a rise in karoshi (i.e., deaths due to being overworked), which reached a record high of ,150 cases per year during 2002–2008 [4]
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