The neural mechanisms underlying the decision to rest in the presence of fatigue: a magnetoencephalography study

Source-Space Brain Functional Connectivity Features in Electroencephalogram-Based Driver Fatigue Classification

This study examined the brain source space functional connectivity from the electroencephalogram (EEG) activity of 48 participants during a driving simulation experiment where they drove until fatigue developed. Source-space functional connectivity (FC) analysis is a state-of-the-art method for understanding connections between brain regions that may indicate psychological differences. Multi-band FC in the brain source space was constructed using the phased lag index (PLI) method and used as features to train an SVM classification model to classify driver fatigue and alert conditions. With a subset of critical connections in the beta band, a classification accuracy of 93% was achieved. Additionally, the source-space FC feature extractor demonstrated superiority over other methods, such as PSD and sensor-space FC, in classifying fatigue. The results suggested that source-space FC is a discriminative biomarker for detecting driving fatigue.

Driving Fatigue Detection with Three Non-Hair-Bearing EEG Channels and Modified Transformer Model

Driving fatigue is the main cause of traffic accidents, which seriously affects people's life and property safety. Many researchers have applied electroencephalogram (EEG) signals for driving fatigue detection to reduce negative effects. The main challenges are the practicality and accuracy of the EEG-based driving fatigue detection method when it is applied on the real road. In our previous study, we attempted to improve the practicality of fatigue detection based on the proposed non-hair-bearing (NHB) montage with fewer EEG channels, but the recognition accuracy was only 76.47% with the random forest (RF) model. In order to improve the accuracy with NHB montage, this study proposed an improved transformer architecture for one-dimensional feature vector classification based on introducing the Gated Linear Unit (GLU) in the Attention sub-block and Feed-Forward Networks (FFN) sub-block of a transformer, called GLU-Oneformer. Moreover, we constructed an NHB-EEG-based feature set, including the same EEG features (power ratio, approximate entropy, and mutual information (MI)) in our previous study, and the lateralization features of the power ratio and approximate entropy based on the strategy of brain lateralization. The results indicated that our GLU-Oneformer method significantly improved the recognition performance and achieved an accuracy of 86.97%. Our framework demonstrated that the combination of the NHB montage and the proposed GLU-Oneformer model could well support driving fatigue detection.

Probiotic Mixture Containing Lactobacillus helveticus, Bifidobacterium longum and Lactiplantibacillus plantarum Affects Brain Responses to an Arithmetic Stress Task in Healthy Subjects: A Randomised Clinical Trial and Proof-of-Concept Study

Probiotics are suggested to impact physiological and psychological stress responses by acting on the gut-brain axis. We investigated if a probiotic product containing Bifidobacterium longum R0175, Lactobacillus helveticus R0052 and Lactiplantibacillus plantarum R1012 affected stress processing in a double-blinded, randomised, placebo-controlled, crossover proof-of-concept study (NCT03615651). Twenty-two healthy subjects (24.2 ± 3.4 years, 6 men/16 women) underwent a probiotic and placebo intervention for 4 weeks each, separated by a 4-week washout period. Subjects were examined by functional magnetic resonance imaging while performing the Montreal Imaging Stress Task (MIST) as well as an autonomic nervous system function assessment during the Stroop task. Reduced activation in regions of the lateral orbital and ventral cingulate gyri was observed after probiotic intervention compared to placebo. Significantly increased functional connectivity was found between the upper limbic region and medioventral area. Interestingly, probiotic intervention seemed to predominantly affect the initial stress response. Salivary cortisol secretion during the task was not altered. Probiotic intervention did not affect cognitive performance and autonomic nervous system function during Stroop. The probiotic intervention was able to subtly alter brain activity and functional connectivity in regions known to regulate emotion and stress responses. These findings support the potential of probiotics as a non-pharmaceutical treatment modality for stress-related disorders.

Look Who’s Talking: Modeling Decision Making Based on Source Credibility

Understanding how humans evaluate credibility is an important scientific question in the era of fake news. Source credibility is among the most important aspects of credibility evaluations. One of the most direct ways to understand source credibility is to use measurements of brain activity of humans who make credibility evaluations. Nevertheless, source credibility has never been investigated using such a method before. This article reports the results of an experiment during which we have measured brain activity during source credibility evaluation using EEG. The experiment allowed for identification of brain areas that were active when a participant made positive or negative source credibility evaluations. Based on experimental data, we modelled and predicted human source credibility evaluations using EEG brain activity measurements with F1 score exceeding 0.7 (using 10-fold cross-validation).

Neural effects of hand-grip-activity induced fatigue sensation on appetite: a magnetoencephalography study

It has been reported that physical activity not only increases energy expenditure, but also affects appetite. However, little remains known about the effects of physical activity-induced fatigue sensation on appetite. In the present study, classical conditioning related to fatigue sensation was used to dissociate fatigue sensation from physical activity. The participants were 20 healthy male volunteers. After overnight fasting, on day 1, the participants performed hand-grip task trials for 10 min with listening to a sound. The next day, they viewed food images with (target task) and without (control task) listening to the sound identical to that used on day 1, and their neural activity during the tasks were recorded using magnetoencephalography. The subjective levels of appetite and fatigue sensation were assessed using a visual analog scale. The subjective level of fatigue increased and that of appetite for fatty foods showed a tendency toward increase in the target task while the subjective level of fatigue and that of appetite for fatty foods were not altered in the control task. In the target task, the decrease of theta (4-8 Hz) band power in the supplementary motor area (SMA), which was observed in the control task, was suppressed, and the suppression was positively correlated with appetite for fatty foods, suggesting hand grip activity-induced fatigue sensation may increase the appetite for fatty food; this increase could be related to neural activity in the SMA. These findings are expected to contribute to the understanding of the neural mechanisms of appetite in relation to fatigue.

Bifidobacterium longum 1714™ Strain Modulates Brain Activity of Healthy Volunteers During Social Stress

OBJECTIVES

Accumulating evidence indicates that the gut microbiota communicates with the central nervous system, possibly through neural, endocrine, and immune pathways, and influences brain function. B. longum 1714™ has previously been shown to attenuate cortisol output and stress responses in healthy subjects exposed to an acute stressor. However, the ability of B. longum 1714™ to modulate brain function in humans is unclear.

METHODS

In a randomized, double-blinded, placebo-controlled trial, the effects of B. longum 1714™ on neural responses to social stress, induced by the "Cyberball game," a standardized social stress paradigm, were studied. Forty healthy volunteers received either B. longum 1714™ or placebo for 4 weeks at a dose of 1 × 10 cfu/d. Brain activity was measured using magnetoencephalography and health status using the 36-item short-form health survey.

RESULTS

B. longum 1714™ altered resting-state neural oscillations, with an increase in theta band power in the frontal and cingulate cortex (P < 0.05) and a decrease in beta-3 band in the hippocampus, fusiform, and temporal cortex (P < 0.05), both of which were associated with subjective vitality changes. All groups showed increased social stress after a 4-week intervention without an effect at behavioral level due to small sample numbers. However, only B. longum 1714™ altered neural oscillation after social stress, with increased theta and alpha band power in the frontal and cingulate cortex (P < 0.05) and supramarginal gyrus (P < 0.05).

DISCUSSION

B. longum 1714™ modulated resting neural activity that correlated with enhanced vitality and reduced mental fatigue. Furthermore, B. longum 1714™ modulated neural responses during social stress, which may be involved in the activation of brain coping centers to counter-regulate negative emotions.

Decreased alpha-band oscillatory brain activity prior to movement initiated by perception of fatigue sensation

Fatigue is a health problem prevalent in modern societies. Fatigue sensation plays an important role as a biological alarm urging rest to maintain homeostasis, and clarifying the neural mechanisms related to fatigue sensations by which we decide to engage in rest is therefore essential. This study enrolled healthy male volunteers and showed that the decrease in alpha-band power as assessed by magnetoencephalography of the left Brodmann's area (BA) 6 before perception of fatigue when a button-press based on the level of fatigue was required was smaller than that before perception of the intention to move when a voluntary button-press was required. In addition, the decrease of alpha-band power in the left BA 6 before the perception of fatigue was not altered compared with that in the right BA 6 when a button-press based on the level of fatigue was required. These results suggest that the button-press based on the perception of fatigue is not prepared before the perception of fatigue. These findings will advance the understanding of the neural mechanisms related to subjective feelings such as fatigue sensation.

Evidence for unconscious regulation of performance in fatigue

Since fatigue is prevalent in modern societies, it is necessary to clarify the neural mechanisms of fatigue. The regulation of performance through fatigue sensation is one of the mechanisms that decreases performance in fatigue. However, it is unknown whether subjective feeling of fatigue is necessary for the regulation of performance. Here, we examined whether decreased performance occurs without increased fatigue sensation through the experiment which was designed to test if fatigue can be learned unconsciously. Healthy male volunteers performed a fatigue-inducing hand-grip task for 10 min while viewing a target image presented without awareness. On the next day, they viewed a control and the target images presented with awareness and the neural activity caused by viewing the images was measured using magnetoencephalography. Results showed the level of fatigue sensation was not altered but grip-strength was decreased by viewing the target image on the second day. The level of beta band power in Brodmann's area 31 was increased by viewing the target image and this increase was negatively associated with the decrease of grip-strength caused in the hand-grip task. These findings demonstrated that fatigue can be learned unconsciously and that there is a mechanism to decrease performance without fatigue sensation.

Neural mechanisms to predict subjective level of fatigue in the future: a magnetoencephalography study

Fatigue is a major contributor to workplace accidents, morbidity, and mortality. To prevent the disruption of homeostasis and to concurrently accomplish an assigned workload, it is essential to control the level of workload based on the subjective estimation of the level of fatigue that will be experienced in the near future. In this study, we aimed to clarify the neural mechanisms related to predicting subjective levels of fatigue that would be experienced 60 min later, using magnetoencephalography. Sixteen healthy male volunteers participated in this study. In relation to the prediction, a decrease of alpha band power in the right Brodmann’s area (BA) 40 and BA 9 at 1200 to 1350 ms and that in the right BA 9 at 1350 to 1500 ms, and a decrease of gamma band power in the right BA 10 at 1500 to 1650 ms were observed. In addition, the decreased level of alpha band power in BA 9 at 1200 to 1350 ms was positively associated with the daily level of fatigue. These findings may help increase our understanding of the neural mechanisms activated to indicate the need to take a rest based on the prediction of the subjective fatigue in the future.

The neural mechanisms of re-experiencing physical fatigue sensation: a magnetoencephalography study

It has been hypothesized that fatigue sensation impairs the ability and efficiency to perform activities and can be a cause of fatigue itself. As such, it is important to clarify the neural mechanisms of fatigue sensation. The re-experiencing of mental fatigue sensation involves brain regions including Brodmann's area (BA) 40, BA 39, and the pulvinar nucleus. In the present study, we examined neural activity caused by re-experiencing a physical fatigue sensation that had been experienced. Fifteen healthy male volunteers participated in fatigue and control experiments in a crossover fashion. In the fatigue experiment, participants performed a handgrip task for 10 min to induce a physical fatigue sensation and then re-experienced the physical fatigue sensation during magnetoencephalography (MEG) session. In the control experiment, they did not perform the handgrip task but re-experienced the sensation without physical fatigue in an MEG session. Neural activity related to re-experiencing physical fatigue sensations of the right hand (right condition), left hand (left condition), and related to listening to the auditory cues (sound condition) was assessed using spatial filtering analyses of the MEG data. Changes in oscillatory band power in some brain regions, including BA 40, were common between the right and left conditions. A part of the neural activity related to the re-experiencing physical fatigue sensation, such as the decrease in alpha (8-13 Hz) band power in the BA 40, was also observed in the sound condition. These findings may help to understand the neural mechanisms related to intentionally and unintentionally re-experiencing physical fatigue sensation.

Frontier studies on fatigue, autonomic nerve dysfunction, and sleep-rhythm disorder

Fatigue is defined as a condition or phenomenon of decreased ability and efficiency of mental and/or physical activities, caused by excessive mental or physical activities, diseases, or syndromes. It is often accompanied by a peculiar sense of discomfort, a desire to rest, and reduced motivation, referred to as fatigue sensation. Acute fatigue is a normal condition or phenomenon that disappears after a period of rest; in contrast, chronic fatigue, lasting at least 6 months, does not disappear after ordinary rest. Chronic fatigue impairs activities and contributes to various medical conditions, such as cardiovascular disease, epileptic seizures, and death. In addition, many people complain of chronic fatigue. For example, in Japan, more than one third of the general adult population complains of chronic fatigue. It would thus be of great value to clarify the mechanisms underlying chronic fatigue and to develop efficient treatment methods to overcome it. Here, we review data primarily from behavioral, electrophysiological, and neuroimaging experiments related to neural dysfunction as well as autonomic nervous system, sleep, and circadian rhythm disorders in fatigue. These data provide new perspectives on the mechanisms underlying chronic fatigue and on overcoming it.