The influence of mental fatigue and motivation on neural network dynamics; an EEG coherence study

Reduced Attention Allocation during Short Periods of Partially Automated Driving: An Event-Related Potentials Study

Research on partially automated driving has revealed relevant problems with driving performance, particularly when drivers' intervention is required (e.g., take-over when automation fails). Mental fatigue has commonly been proposed to explain these effects after prolonged automated drives. However, performance problems have also been reported after just a few minutes of automated driving, indicating that other factors may also be involved. We hypothesize that, besides mental fatigue, an underload effect of partial automation may also affect driver attention. In this study, such potential effect was investigated during short periods of partially automated and manual driving and at different speeds. Subjective measures of mental demand and vigilance and performance to a secondary task (an auditory oddball task) were used to assess driver attention. Additionally, modulations of some specific attention-related event-related potentials (ERPs, N1 and P3 components) were investigated. The mental fatigue effects associated with the time on task were also evaluated by using the same measurements. Twenty participants drove in a fixed-base simulator while performing an auditory oddball task that elicited the ERPs. Six conditions were presented (5-6 min each) combining three speed levels (low, comfortable and high) and two automation levels (manual and partially automated). The results showed that, when driving partially automated, scores in subjective mental demand and P3 amplitudes were lower than in the manual conditions. Similarly, P3 amplitude and self-reported vigilance levels decreased with the time on task. Based on previous studies, these findings might reflect a reduction in drivers' attention resource allocation, presumably due to the underload effects of partial automation and to the mental fatigue associated with the time on task. Particularly, such underload effects on attention could explain the performance decrements after short periods of automated driving reported in other studies. However, further studies are needed to investigate this relationship in partial automation and in other automation levels.

Self-Regulatory Capacities Are Depleted in a Domain-Specific Manner

Performing an act of self-regulation such as making decisions has been suggested to deplete a common limited resource, which impairs all subsequent self-regulatory actions (ego depletion theory). It has however remained unclear whether self-referred decisions truly impair behavioral control even in seemingly unrelated cognitive domains, and which neurophysiological mechanisms are affected by these potential depletion effects. In the current study, we therefore used an inter-individual design to compare two kinds of depletion, namely a self-referred choice-based depletion and a categorization-based switching depletion, to a non-depleted control group. We used a backward inhibition (BI) paradigm to assess the effects of depletion on task switching and associated inhibition processes. It was combined with EEG and source localization techniques to assess both behavioral and neurophysiological depletion effects. The results challenge the ego depletion theory in its current form: Opposing the theory’s prediction of a general limited resource, which should have yielded comparable effects in both depletion groups, or maybe even a larger depletion in the self-referred choice group, there were stronger performance impairments following a task domain-specific depletion (i.e., the switching-based depletion) than following a depletion based on self-referred choices. This suggests at least partly separate and independent resources for various cognitive control processes rather than just one joint resource for all self-regulation activities. The implications are crucial to consider for people making frequent far-reaching decisions e.g., in law or economy.

Cognitive fatigue in individuals with traumatic brain injury is associated with caudate activation

We investigated differences in brain activation associated with cognitive fatigue between persons with traumatic brain injury (TBI) and healthy controls (HCs). Twenty-two participants with moderate-severe TBI and 20 HCs performed four blocks of a difficult working memory task and four blocks of a control task during fMRI imaging. Cognitive fatigue, assessed before and after each block, was used as a covariate to assess fatigue-related brain activation. The TBI group reported more fatigue than the HCs, though their performance was comparable. Regarding brain activation, the TBI group showed a Task X Fatigue interaction in the caudate tail resulting from a positive correlation between fatigue and brain activation for the difficult task and a negative relationship for the control task. The HC group showed the same Task X Fatigue interaction in the caudate head. Because we had prior hypotheses about the caudate, we performed a confirmatory analysis of a separate dataset in which the same subjects performed a processing speed task. A relationship between Fatigue and brain activation was evident in the caudate for this task as well. These results underscore the importance of the caudate nucleus in relation to cognitive fatigue.

Effects of mental workload on involuntary attention: A somatosensory ERP study

Previous psychophysiological assessments of mental workload have relied on the addition of visual or auditory stimuli. This study investigated the tactile ERP and EEG spectral power correlates of mental workload by relating limited-capacity involuntary attention allocation to changes in late positive potential (LPP) amplitude, alpha, and theta powers. We examined whether mental workload (high-level cognitive control) can be evaluated using somatosensory stimuli. Sixteen participants all performed three tasks of varying difficulty. Two dual n-back tasks (n = 1 and 2) were used to investigate the degree to which mental workload affected the LPP amplitudes and EEG spectral powers evoked by ignoring salient tactile stimuli. In control trials, tactile vibrations were applied at random without dual n-back tasks. Subjective mental workload of each task was rated using the NASA Task Load Index. LPP amplitudes at Pz were significantly smaller in the dual-2-back trials compared to control and dual-1-back trials. Significantly increased theta power at Fz and reduced alpha power at Pz were found in the dual-2-back condition compared to control and dual-1-back condition. There was no significant difference between control and dual-1-back trials. The same pattern was found for subjective ratings of cognitive workload. These results indicate that the dual-2-back task imposed a significantly greater mental workload, causing impaired cognitive-control functions. Our findings support the notion that selective attention mechanisms necessary for effectively allocating and modulating attentional resources are temporarily impaired during the mentally overloaded state.

Young and Middle-Aged Schoolteachers Differ in the Neural Correlates of Memory Encoding and Cognitive Fatigue: A Functional MRI Study

This investigation was inspired by growing evidence that middle-aged persons in a cognitively demanding profession might be characterized by subtle cognitive fatigue. We studied young and middle-aged male schoolteachers. They were compared in a study with functional magnetic resonance imaging to evaluate differences during successful memory encoding. The schoolteachers were additionally subjected to an induced fatigue condition involving the sustained performance of cognitively demanding tasks and to a control condition. Results showed age-related brain activation differences underlying behavioral performance including: (1) greater activation in middle-aged vs. young teachers in bilateral prefrontal cortex (PFC) areas; and (2) differential fatigue effects in the left anterior cingulate cortex (ACC) depending on age group. Middle-aged schoolteachers showed decreased ACC activation in the fatigue compared to the control condition, whereas no change in activation was found in young teachers. Findings demonstrate age effects in these middle-aged subjects that are typically found in older adults, specifically in PFC over-activation. Findings also indicate that already in middle age cognitive aging may be associated with greater resource depletion following sustained task performance. The findings underscore the notion that persons in a cognitively demanding profession can experience subtle age effects, which are evident on fMRI and which impact daily functioning. Possible practical implications for middle-aged schoolteachers are discussed.

Basal ganglia correlates of fatigue in young adults

Although the prevalence of chronic fatigue is approximately 20% in healthy individuals, there are no studies of brain structure that elucidate the neural correlates of fatigue outside of clinical subjects. We hypothesized that fatigue without evidence of disease might be related to changes in the basal ganglia and prefrontal cortex and be implicated in fatigue with disease. We aimed to identify the white matter structures of fatigue in young subjects without disease using magnetic resonance imaging (MRI). Healthy young adults (n = 883; 489 males and 394 females) were recruited. As expected, the degrees of fatigue and motivation were associated with larger mean diffusivity (MD) in the right putamen, pallidus and caudate. Furthermore, the degree of physical activity was associated with a larger MD only in the right putamen. Accordingly, motivation was the best candidate for widespread basal ganglia, whereas physical activity might be the best candidate for the putamen. A plausible mechanism of fatigue may involve abnormal function of the motor system, as well as areas of the dopaminergic system in the basal ganglia that are associated with motivation and reward.

Investigating the Effects of Peripheral Electrical Stimulation on Corticomuscular Functional Connectivity Stroke Survivors

BACKGROUND

Electrical stimulation (ES) in the periphery can induce brain plasticity and has been used clinically to promote motor recovery in patients with central nervous system lesion. Electroencephalogram (EEG) and electromyogram (EMG) are readily applicable in clinical settings and can detect real-time functional connectivity between motor cortex and muscles with EEG-EMG (corticomuscular) coherence.

OBJECTIVE

The purpose of this study was to determine whether EEG-EMG coherence can detect changes in corticomuscular control induced by peripheral ES.

METHODS

Fifteen healthy young adults and 15 stroke survivors received 40-min electrical stimulation session on median nerve. The stimulation (1-ms rectangular pulse, 100 Hz) was delivered with a 20-s on-20-s off cycle, and the intensity was set at the subjects' highest tolerable level without muscle contraction or pain. Both before and after the stimulation session, subjects performed a 20-s steady-hold thumb flexion at 50% maximal voluntary contraction (MVC) while EEG and EMG were collected.

RESULTS

Our results demonstrated that after ES, EEG-EMG coherence in gamma band increased significantly for 22.1 and 48.6% in healthy adults and stroke survivors, respectively. In addition, after ES, force steadiness was also improved in both groups, as indicated by the decrease in force fluctuation during steady-hold contraction (-1.7% MVC and -3.9%MVC for healthy and stroke individuals, respectively).

CONCLUSIONS

Our results demonstrated that EEG-EMG coherence can detect ES-induced changes in the neuromuscular system. Also, because gamma coherence is linked to afferent inputs encoding, improvement in motor performance is likely related to ES-elicited strong sensory input and enhanced sensorimotor integration.

Dissociation between mental fatigue and motivational state during prolonged mental activity

Mental fatigue (MF) is commonly observed following prolonged cognitive activity and can have major repercussions on the daily life of patients as well as healthy individuals. Despite its important impact, the cognitive processes involved in MF remain largely unknown. An influential hypothesis states that MF does not arise from a disruption of overused neural processes but, rather, is caused by a progressive decrease in motivation-related task engagement. Here, to test this hypothesis, we measured various neural, autonomic, psychometric and behavioral signatures of MF and motivation (EEG, ECG, pupil size, eye blinks, Skin conductance responses (SCRs), questionnaires and performance in a working memory (WM) task) in healthy volunteers, while MF was induced by Sudoku tasks performed for 120 min. Moreover extrinsic motivation was manipulated by using different levels of monetary reward. We found that, during the course of the experiment, the participants’ subjective feeling of fatigue increased and their performance worsened while their blink rate and heart rate variability (HRV) increased. Conversely, reward-induced EEG, pupillometric and skin conductance signal changes, regarded as indicators of task engagement, remained constant during the experiment, and failed to correlate with the indices of MF. In addition, MF did not affect a simple reaction time task, despite the strong influence of extrinsic motivation on this task. Finally, alterations of the motivational state through monetary incentives failed to compensate the effects of MF. These findings indicate that MF in healthy subjects is not caused by an alteration of task engagement but is likely to be the consequence of a decrease in the efficiency, or availability, of cognitive resources.

The Effects of Time on Task in Response Selection--An ERP Study of Mental Fatigue

Long lasting involvement in a cognitive task leads to mental fatigue. Substantial efforts have been undertaken to understand this phenomenon. However, it has been demonstrated that some changes with time on task are not only related to mental fatigue. The present study intends to clarify these effects of time on task unrelated to mental fatigue on response selection processes at the behavioural and electrophysiological level (using event-related potentials, ERPs). Participants had to perform a Simon task for more than 3 hours and rated their experienced mental fatigue and motivation to continue with the task at several time points during the experiment. The results show that at the beginning of the experiment some unspecific modulations of training and adaptation are evident. With time on task participants' ability to resolve response conflict appears to become impaired. The results reveal that time on task effects cannot be completely explained by mental fatigue. Instead, it seems that an interplay of adaptation at the beginning and motivational effects in the course of a task modulate performance and neurophysiological parameters. In future studies it will be important to account for the relative contribution of adaptation and motivation parameters when time on task effects are investigated.

Neural mechanisms of mental fatigue

Fatigue is defined as a decline in the ability and efficiency of mental and/or physical activities that is caused by excessive mental and/or physical activities. Fatigue can be classified as physical or mental. Mental fatigue manifests as potentially impaired cognitive function and is one of the most significant causes of accidents in modern society. Recently, it has been shown that the neural mechanisms of mental fatigue related to cognitive task performance are more complex than previously thought and that mental fatigue is not caused only by impaired activity in task-related brain regions. There is accumulating evidence supporting the existence of mental facilitation and inhibition systems. These systems are involved in the neural mechanisms of mental fatigue, modulating the activity of task-related brain regions to regulate cognitive task performance. In this review, we propose a new conceptual model: the dual regulation system of mental fatigue. This model contributes to our understanding of the neural mechanisms of mental fatigue and the regulatory mechanisms of cognitive task performance in the presence of mental fatigue.

The Effects of Cognitive Control and Time on Frontal Beta Oscillations

Frontal beta oscillations are associated with top-down control mechanisms but also change over time during a task. It is unclear whether change over time represents another control function or a neural instantiation of vigilance decrements over time, the time-on-task effect. We investigated how frontal beta oscillations are modulated by cognitive control and time. We used frontal chronic electrocorticography in monkeys performing a trial-and-error task, comprising search and repetition phases. Specific beta oscillations in the delay period of each trial were modulated by task phase and adaptation to feedback. Beta oscillations in this same period showed a significant within-session change. These separate modulations of beta oscillations did not interact. Crucially, and in contrast to previous investigations, we examined modulations of beta around spontaneous pauses in work. After pauses, the beta power modulation was reset and the cognitive control effect was maintained. Cognitive performance was also maintained whereas behavioral signs of fatigue continued to increase. We propose that these beta oscillations reflect multiple factors contributing to the regulation of cognitive control. Due to the effect of pauses, the time-sensitive factor cannot be a neural correlate of time-on-task but may reflect attentional effort.

Effect of mental fatigue caused by mobile 3D viewing on selective attention: an ERP study

This study investigated behavioral responses to and auditory event-related potential (ERP) correlates of mental fatigue caused by mobile three-dimensional (3D) viewing. Twenty-six participants (14 women) performed a selective attention task in which they were asked to respond to the sounds presented at the attended side while ignoring sounds at the ignored side before and after mobile 3D viewing. Considering different individual susceptibilities to 3D, participants' subjective fatigue data were used to categorize them into two groups: fatigued and unfatigued. The amplitudes of d-ERP components were defined as differences in amplitudes between time-locked brain oscillations of the attended and ignored sounds, and these values were used to calculate the degree to which spatial selective attention was impaired by 3D mental fatigue. The fatigued group showed significantly longer response times after mobile 3D viewing compared to before the viewing. However, response accuracy did not significantly change between the two conditions, implying that the participants used a behavioral strategy to cope with their performance accuracy decrement by increasing their response times. No significant differences were observed for the unfatigued group. Analysis of covariance revealed group differences with significant and trends toward significant decreases in the d-P200 and d-late positive potential (LPP) amplitudes at the occipital electrodes of the fatigued and unfatigued groups. Our findings indicate that mentally fatigued participants did not effectively block out distractors in their information processing mechanism, providing support for the hypothesis that 3D mental fatigue impairs spatial selective attention and is characterized by changes in d-P200 and d-LPP amplitudes.

Decreased coherence and functional connectivity of electroencephalograph in Alzheimer's disease

In this paper, we investigate the abnormalities of electroencephalograph (EEG) signals in the Alzheimer's disease (AD) by analyzing 16-scalp electrodes EEG signals and make a comparison with the normal controls. Coherence is introduced to measure the pair-wise normalized linear synchrony and functional correlations between two EEG signals in different frequency domains, and graph analysis is further used to investigate the influence of AD on the functional connectivity of human brain. Data analysis results show that, compared with the control group, the pair-wise coherence of AD group is significantly decreased, especially for the theta and alpha frequency bands in the frontal and parieto-occipital regions. Furthermore, functional connectivity among different brain regions is reconstructed based on EEG, which exhibit obvious small-world properties. Graph analysis demonstrates that the local functional connections between regions for AD decrease. In addition, it is found that small-world properties of AD networks are largely weakened, by calculating its average path lengths, clustering coefficients, global efficiency, local efficiency, and small-worldness. The obtained results show that both pair-wise coherence and functional network can be taken as effective measures to distinguish AD patients from the normal, which may benefit our understanding of the disease.

Estimating endogenous changes in task performance from EEG

Brain wave activity is known to correlate with decrements in behavioral performance as individuals enter states of fatigue, boredom, or low alertness.Many BCI technologies are adversely affected by these changes in user state, limiting their application and constraining their use to relatively short temporal epochs where behavioral performance is likely to be stable. Incorporating a passive BCI that detects when the user is performing poorly at a primary task, and adapts accordingly may prove to increase overall user performance. Here, we explore the potential for extending an established method to generate continuous estimates of behavioral performance from ongoing neural activity; evaluating the extended method by applying it to the original task domain, simulated driving; and generalizing the method by applying it to a BCI-relevant perceptual discrimination task. Specifically, we used EEG log power spectra and sequential forward floating selection (SFFS) to estimate endogenous changes in behavior in both a simulated driving task and a perceptual discrimination task. For the driving task the average correlation coefficient between the actual and estimated lane deviation was 0.37 ± 0.22 (μ ± σ). For the perceptual discrimination task we generated estimates of accuracy, reaction time, and button press duration for each participant. The correlation coefficients between the actual and estimated behavior were similar for these three metrics (accuracy = 0.25 ± 0.37, reaction time = 0.33 ± 0.23, button press duration = 0.36 ± 0.30). These findings illustrate the potential for modeling time-on-task decrements in performance from concurrent measures of neural activity.

Effect of mental fatigue on induced tremor in human knee extensors

In this study, the effects of mental fatigue on mechanically induced tremor at both a low (3-6Hz) and high (8-12Hz) frequency were investigated. The two distinct tremor frequencies were evoked using two springs of different stiffness, during 20s sustained contractions of the knee extensor muscles at 30% maximum voluntary contraction (MVC) before and after 100min of a mental fatigue task, in 12 healthy (29±3.7years) participants. Mental fatigue resulted in a 6.9% decrease in MVC and in a 9.4% decrease in the amplitude of the agonist muscle EMG during sustained 30% MVC contractions in the induced high frequency only. Following the mental fatigue task, the coefficient of variation and standard deviation of the force signal decreased at 8-12Hz induced tremor by 31.7% and 35.2% respectively, but not at 3-6Hz induced tremor. Similarly, the maximum value and area underneath the peak in the power spectrum of the force signal decreased by 55.5% and 53.1% respectively in the 8-12Hz range only. In conclusion, mental fatigue decreased mechanically induced 8-12Hz tremor and had no effect on induced 3-6Hz tremor. We suggest that the reduction could be attributed to the decreased activation of the agonist muscles.

Neural correlates of cognitive fatigue: cortico-striatal circuitry and effort-reward imbalance

Recently, there has been renewed interest in the study of cognitive fatigue. It is known that fatigue is one of the most disabling symptoms in numerous neurological populations, including stroke, multiple sclerosis, Parkinson’s disease, and traumatic brain injury. Behavioral studies of cognitive fatigue are hampered by lack of correlation of self-report measures with objective performance. Neuroimaging studies provide new insight about cognitive fatigue and its neural correlates.Impairment within the cortico-striatal network, involved in effort–reward calculation, has been suggested to be critically related to fatigue. The current review surveys the recent neuroimaging literature, and suggests promising avenues for future research.

Physiological load and posture control thresholds

The aim of the study was to evaluate the influence of the physiological load on postural control. Special attention was directed toward the identifying the intensity level in which the major deterioration in balance abilities occurs. Thirty subjects randomly divided into two groups performed multistage all-out exertion protocol on cycle-ergometer with measurements of ventilatory-metabolic and subjective parameters of exertion. Each stage lasted three minutes and was followed with three minute breaks during which the subjects underwent the static (keeping the cursor in the center of the screen) and the dynamic balance testing (following the cursor clockwise or counter clock wise by body movements) on balance platform. In a control group, the protocol encompassed only balance testing procedures followed by 3 min rest. After the completion of the testing procedures, the five intensity zones were determined according to the ventilatory-metabolic parameters. The significant differences in both static and dynamic balance tests were found between the test stages in exercising group. The post hoc analyses revealed the significant negative effect of exercise on the static balance with three visible "balance thresholds". The first threshold was at the rest to work transition, the second at the anaerobic threshold and the third at the maximal exertion level. The dynamic balance was also negatively affected with exercise, however no "balance thresholds" were clearly identified. No significant changes in neither static nor dynamic balance abilities were observed in the control group so the changes in the experimental group could have been attributed to the exercise intensity.

Dopaminergic involvement during mental fatigue in health and cocaine addiction

Dopamine modulates executive function, including sustaining cognitive control during mental fatigue. Using event-related functional magnetic resonance imaging (fMRI) during the color-word Stroop task, we aimed to model mental fatigue with repeated task exposures in 33 cocaine abusers and 20 healthy controls. During such mental fatigue (indicated by increased errors, and decreased post-error slowing and dorsal anterior cingulate response to error as a function of time-on-task), healthy individuals showed increased activity in the dopaminergic midbrain to error. Cocaine abusers, characterized by disrupted dopamine neurotransmission, showed an opposite pattern of response. This midbrain fMRI activity with repetition was further correlated with objective indices of endogenous motivation in all subjects: a state measure (task reaction time) and a trait measure (dopamine D2 receptor availability in caudate, as revealed by positron emission tomography data collected in a subset of this sample, which directly points to a contribution of dopamine to these results). In a second sample of 14 cocaine abusers and 15 controls, administration of an indirect dopamine agonist, methylphenidate, reversed these midbrain responses in both groups, possibly indicating normalization of response in cocaine abusers because of restoration of dopamine signaling but degradation of response in healthy controls owing to excessive dopamine signaling. Together, these multimodal imaging findings suggest a novel involvement of the dopaminergic midbrain in sustaining motivation during fatigue. This region might provide a useful target for strengthening self-control and/or endogenous motivation in addiction.

EEG oscillations reveal neural correlates of evidence accumulation

Recent studies have begun to elucidate the neural correlates of evidence accumulation in perceptual decision making, but few of them have used a combined modeling-electrophysiological approach to studying evidence accumulation. We introduce a multivariate approach to EEG analysis with which we can perform a comprehensive search for the neural correlate of dynamics predicted by accumulator models. We show that the dynamics of evidence accumulation are most strongly correlated with ramping of oscillatory power in the 4-9 Hz theta band over the course of a trial, although it also correlates with oscillatory power in other frequency bands. The rate of power decrease in the theta band correlates with individual differences in the parameters of drift diffusion models fitted to individuals' behavioral data.

Effects of a multi-vitamin/mineral supplement on cognitive function and fatigue during extended multi-tasking

OBJECTIVES

A significant minority of the population consume multi-vitamins/minerals for their putative health benefits, including potentially beneficial effects on cognitive performance, fatigue and mood. The current study investigated the effect of supplementation with a multi-vitamin/mineral on fatigue and cognitive function in healthy females.

METHODS

In this placebo-controlled, double blind, randomized, parallel groups trial the effect of a multi-vitamin/mineral (Supradyn) was assessed in 216 females aged 25-50 years. Participants attended the laboratory before and 9 weeks after commencing treatment. During both visits cognitive function and the modulation of task related mood/fatigue were assessed in two discrete 20-min assessment periods during which participants completed a four-module version of the Multi-Tasking Framework.

RESULTS

Those in the vitamin/mineral group exhibited an attenuation of the negative effects of extended task completion on mood/fatigue. Multi-tasking performance for this group was also improved in terms of accuracy across all tasks, and on two of the individual tasks (Mathematical Processing and Stroop) in terms of both faster and more accurate responses. Analysis of a subsection (N = 102) demonstrated significant reductions in homocysteine levels following the vitamins/mineral supplement.

CONCLUSIONS

These findings suggest that healthy members of the general population may benefit from augmented levels of vitamins/minerals via direct dietary supplementation.

Effects of high-dose B vitamin complex with vitamin C and minerals on subjective mood and performance in healthy males

RATIONALE

A significant proportion of the general population report supplementing their diet with one or more vitamins or minerals, with common reasons for doing so being to combat stress and fatigue and to improve mental functioning. Few studies have assessed the relationship between supplementation with vitamins/minerals and psychological functioning in healthy cohorts of non-elderly adults.

OBJECTIVES

The present randomised, placebo-controlled, double-blind, parallel groups trial assessed the cognitive and mood effects of a high-dose B-complex vitamin and mineral supplement (Berocca(R)) in 215 males aged 30 to 55 years, who were in full-time employment.

METHODS

Participants attended the laboratory prior to and on the last day of a 33-day treatment period where they completed the Profile of Mood States (POMS), Perceived Stress Scale (PSS) and General Health Questionnaire (GHQ-12). Cognitive performance and task-related modulation of mood/fatigue were assessed with the 60 min cognitive demand battery. On the final day, participants also completed the Stroop task for 40 min whilst engaged in inclined treadmill walking and subsequent executive function was assessed.

RESULTS

Vitamin/mineral supplementation led to significant improvements in ratings on the PSS, GHQ-12 and the 'vigour' subscale of the POMS. The vitamin/mineral group also performed better on the Serial 3s subtractions task and rated themselves as less 'mentally tired' both pre- and post-completion of the cognitive demand battery.

CONCLUSIONS

Healthy members of the general population may benefit from augmented levels of vitamins/minerals via direct dietary supplementation. Specifically, supplementation led to improved ratings of stress, mental health and vigour and improved cognitive performance during intense mental processing.

Effects of high-dose B vitamin complex with vitamin C and minerals on subjective mood and performance in healthy males

RATIONALE

A significant proportion of the general population report supplementing their diet with one or more vitamins or minerals, with common reasons for doing so being to combat stress and fatigue and to improve mental functioning. Few studies have assessed the relationship between supplementation with vitamins/minerals and psychological functioning in healthy cohorts of non-elderly adults.

OBJECTIVES

The present randomised, placebo-controlled, double-blind, parallel groups trial assessed the cognitive and mood effects of a high-dose B-complex vitamin and mineral supplement (Berocca(R)) in 215 males aged 30 to 55 years, who were in full-time employment.

METHODS

Participants attended the laboratory prior to and on the last day of a 33-day treatment period where they completed the Profile of Mood States (POMS), Perceived Stress Scale (PSS) and General Health Questionnaire (GHQ-12). Cognitive performance and task-related modulation of mood/fatigue were assessed with the 60 min cognitive demand battery. On the final day, participants also completed the Stroop task for 40 min whilst engaged in inclined treadmill walking and subsequent executive function was assessed.

RESULTS

Vitamin/mineral supplementation led to significant improvements in ratings on the PSS, GHQ-12 and the 'vigour' subscale of the POMS. The vitamin/mineral group also performed better on the Serial 3s subtractions task and rated themselves as less 'mentally tired' both pre- and post-completion of the cognitive demand battery.

CONCLUSIONS

Healthy members of the general population may benefit from augmented levels of vitamins/minerals via direct dietary supplementation. Specifically, supplementation led to improved ratings of stress, mental health and vigour and improved cognitive performance during intense mental processing.

Brain biomarkers of motor adaptation using phase synchronization

A growing number of brain monitoring tools for medical and biomedical applications such as surgery have been developed. Although many assistive technologies (e.g., brain computer interface (BCI) systems) aiming to restore cognitive-motor deficits are under development, no functional neural indicator or brain biomarker able to track the cortical dynamics of the brain when interacting with new tools and/or novel environments in ecological situations are available. Therefore this study aimed to investigate potential biomarkers reflecting the dynamic cognitive-motor states of subjects who had to learn a new tool. These biomarkers were derived from phase synchronization measures of electroencephalographic (EEG) signals (coherence, phase locking value (PLV)). The findings indicate a linear decrease of phase synchronization for both movement planning and execution as subjects adapt during tool learning. These changes were correlated with enhanced kinematics as the task progressed. These non-invasive biomarkers may play a role in bioengineering applications and particularly in BCI systems, allowing the establishment of co-adaptation/cooperation between the user's brain and the decoding algorithm to design adaptive neuroprostheses.