The influence of mental fatigue on brain activity: Evidence from a systematic review with meta‐analyses

Abstract

The occurrence of mental fatigue during tasks like driving a vehicle increases risk of injury or death. Changes in electroencephalographic (EEG) activity associated with mental fatigue has been frequently studied and considered a promising biomarker of mental fatigue. This is despite differences in methodologies and outcomes in prior research. A systematic review with meta‐analyses was conducted to establish the influence of mental fatigue on EEG activity spectral bands, and to determine in which regions fatigue‐related EEG spectral changes are likely to occur. A high‐yield search strategy identified 21 studies meeting inclusion criteria for investigating the change in EEG spectral activity in non‐diseased adults engaged in mentally fatiguing tasks. A medium effect size (using Cohen's g) of 0.68 (95%CI: 0.24–1.13) was found for increase in overall EEG activity following mental fatigue. Further examination of individual EEG spectral bands and regions using network meta‐analyses indicated large increases in theta (g = 1.03; 95%CI: 0.79–1.60) and alpha bands (g = 0.85; 95%CI: 0.47–1.43), with small to moderate changes found in delta and beta bands. Central regions of the scalp showed largest change (g = 0.80; 95%CI: 0.46–1.21). Sub‐group analyses indicated large increases in theta activity in frontal, central and posterior sites (all g > 1), with moderate changes in alpha activity in central and posterior sites. Findings have implications for fatigue monitoring and countermeasures with support for change in theta activity in frontal, central and posterior sites as a robust biomarker of mental fatigue and change in alpha wave activity considered a second line biomarker to account for individual variability.

Mental Fatigue Might Be Not So Bad for Exercise Performance After All: A Systematic Review and Bias-Sensitive Meta-Analysis

“…In addition, though little is known in this regard, mental fatigue accrued over consecutive days might have a stronger influence on exercise performance than the typical one-session manipulation used to date (Russell, Jenkins, Smith, Halson, & Kelly, 2019). Researchers could use the "rating of fatigue scale" (Micklewright, St Clair Gibson, Gladwell, & Al Salman, 2017) together with additional objective indexes of fatigue (e.g., brain activity; Tran, Craig, Craig, Chai, & Nguyen, 2020;Wang et al, 2016), to assess the multifaceted nature of fatigue (Enoka & Duchateau, 2016).…”

Specific Increase of Hippocampal Delta Oscillations Across Consecutive Treadmill Runs

“…Finally, we have proposed above that the changes in delta power observed here could signal the development of fatigue. Complementary to this hypothesis, the reduction in theta and gamma band power could also be related to the neural resources available to perform the running exercise (Tulving and Rosenbaum, 2006;Lohnas et al, 2015;Poldrack, 2015;Cheron et al, 2016;Tran et al, 2020). In this way, reductions of theta and gamma power would indicate a decrease in the internal readiness to perform the motor act.…”

“…Alternatively, we propose that the increase of hippocampal delta power and inter-hemispheric coherence across successive runs could reflect the development of fatigue. The role of neuronal oscillations underlying the mechanisms of central fatigue remains unclear, but the signaling of fatigue in the brain may take place even before any reduction in performance outputs (Davis and Bailey, 1997;Lohnas et al, 2015;Cheron et al, 2016;Tran et al, 2020). According to this view, the brain processes that support the maintenance of running exercise cannot be sustained indefinitely but depend on neural resources that are progressively depleted along periods of high activity (Tulving and Rosenbaum, 2006;Poldrack, 2015).…”

Persistence of Mental Fatigue on Motor Control

“…Mainly an increase in alpha power has consistently been observed, which might reflect a decrease in arousal and alertness (Paus et al, 1997;Boksem et al, 2005;Zhao et al, 2012). Although alpha power changes are a robust marker of mental fatigue, a recent meta-analysis suggested that an increase in theta power would be a more reliable biomarker of the presence of mental fatigue (Tran et al, 2020). According to this meta-analysis, mental fatigue results in large increases in theta power through the whole brain (i.e., frontal, central, and posterior regions), while increases in alpha power are mainly observed in central and posterior regions and to a lesser extent in frontal regions.…”