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Caffeine can be used effectively to manipulate our mental state. It is beneficial in restoring low levels of wakefulness and in counteracting degraded cognitive task performance due to sleep deprivation. However, caffeine may produce detrimental effects on subsequent sleep, resulting in daytime sleepiness. This justifies a careful consideration of risks related to sleep deprivation in combination with caffeine consumption, especially in adolescents. The efficacy of caffeine to restore detrimental effects of sleep deprivation seems to be partly due to caffeine expectancy and to placebo effects. The claim that stimulant effects of caffeine are related to withdrawal or withdrawal reversal seems to be untenable., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The purpose of the present study is to examine the effects of mental fatigue and motivation on neural network dynamics activated during task switching. Mental fatigue was induced by 2 h of continuous performance; after which subjects were motivated by using social comparison and monetary reward as motivating factors to perform well for an additional 20 min. EEG coherence was used as a measure of synchronization of brain activity. Electrodes of interest were identified using a data-driven pre-processing method (ten Caat, M., Lorist, M.M., Bezdan, E., Roerdink, J.B.T.M., Maurits, N.M., 2008a. High-density EEG coherence analysis using functional units applied to mental fatigue. J. Neurosci. Meth. 171, 271-278; ten Caat, M., Maurits, N.M. and Roerdink, J.B.T.M., 2008b. Data-driven visualization and group analysis of multichannel EEG coherence with functional units. IEEE T. Vis. Comp. Gr. 14, 756-771). Performance on repetition trials was faster and more accurate than on switch trials. EEG data revealed more pronounced, frequency specific fronto-parietal network activation in switch trials, while power density was higher in repetition trials. The effects of mental fatigue on power and coherence were widespread, and not limited to specific frequency bands. Moreover, these effects were independent of specific task manipulations. This increase in neuronal activity and stronger synchronization between neural networks did not result in more efficient performance; response speed decreased and the number of errors increased in fatigued subjects. A modulation of the dopamine system is proposed as a common mechanism underlying the observed the fatigue effects.

Objective: A dual task paradigm was used to examine the effects of the generation of force on cognitive performance., Methods: Subjects (n=22) were asked to respond to auditory stimuli with their left middle or index finger and concurrently maintain a sub-maximal contraction with their right index finger at one of two different force levels. The contraction was maintained for approximately 12s and the target force level was alternated between 30 and 60% of the maximal force. Force production was the primary task of interest; performance of the (secondary) choice reaction time task (reaction times and accuracy) was used as an index of the amount of interference between the two tasks., Results: All subjects were capable of performing the force tasks adequately. Significant interference was observed between the level of force production and cognitive performance. At the higher force level, subjects performed the cognitive task more slowly and less accurately compared to the lower force level., Conclusion: Our results show that the execution of high-effort motor behaviour interacts with cognitive task performance. However, comparison with the data obtained during fatiguing contractions in a previous study [Lorist MM, Kernell D, Meijman TF, Zijdewind I. Motor fatigue and cognitive task performance in humans. J Physiol 2002;545:313-319.] showed that the interference was stronger during fatiguing contractions than during the present high-effort motor behaviour., Significance: The results suggest that force-related factors can explain part of the fatigue-related interference between force production and cognitive performance. This result could have consequences for interpreting cognitive deficits observed in patients suffering from motor dysfunction.

Rationale: In everyday life, people are usually capable of performing two tasks simultaneously. However, in a previous study we showed that during a fatiguing motor task, cognitive performance declined progressively. There is extensive literature on the (positive) effects of caffeine on cognitive and motor performance. These effects are most pronounced under suboptimal conditions, for example during fatigue. However, little is known about the effects of caffeine on cognitive performance during a fatiguing motor task., Objective: This study was aimed to investigate whether a moderate dose of caffeine could attenuate the decline in cognitive performance during a fatiguing motor task., Methods: The study consisted of a placebo and a caffeine (3 mg/kg) session. A total of 23 subjects completed these sessions in a semi-randomized and double-blind order. In each session, subjects performed maximal voluntary contractions of the index finger, a choice reaction time (CRT) task and a dual task consisting of a fatiguing motor task concomitantly with the same CRT task. After the fatiguing dual task, the CRT task was repeated., Results: Caffeine improved cognitive task performance, in both the single and dual task, as shown by decreased reaction times together with unchanged accuracy. Cognitive performance in the dual task deteriorated with increasing fatigue. However, the decrease in cognitive performance in the beginning of the dual task, as observed in the placebo condition, was partly prevented by caffeine administration (i.e., no increase in reaction times). We found no effects of caffeine on motor parameters (absolute force, endurance time or electromyographic amplitude)., Conclusions: Caffeine improved cognitive performance. This effect also extends under demanding situations, as was shown by the performance during the dual task, even during progressive motor fatigue.

Effects of caffeine and fatigue are discussed with special attention to adenosine-dopamine interactions. Effects of caffeine on human cognition are diverse. Behavioural measurements indicate a general improvement in the efficiency of information processing after caffeine, while the EEG data support the general belief that caffeine acts as a stimulant. Studies using ERP measures indicate that caffeine has an effect on attention, which is independent of specific stimulus characteristics. Behavioural effects on response related processes turned out to be mainly related to more peripheral motor processes. Recent insights in adenosine and dopamine physiology and functionality and their relationships with fatigue point to a possible modulation by caffeine of mechanisms involved in the regulation of behavioural energy expenditure.

During fatiguing submaximal contractions a constant force production can be obtained at the cost of an increasing central command intensity. Little is known about the interaction between the underlying central mechanisms driving motor behaviour and cognitive functions. To address this issue, subjects performed four tasks: an auditory choice reaction task (CRT), a CRT simultaneously with a fatiguing or a non-fatiguing submaximal muscle contraction task, and a fatiguing submaximal contraction task alone. Results showed that performance in the single-CRT condition was relatively stable. However, in the fatiguing dual-task condition, performance levels in the cognitive CRT deteriorated drastically with time-on-task. Moreover, in the fatiguing dual-task condition the rise in force variability was significantly larger than during the fatiguing submaximal contraction alone. Thus, our results indicate a mutual interaction between cognitive functions and the central mechanisms driving motor behaviour during fatigue. The precise nature of this interference, and at what level this interaction takes place is still unknown.

Although many educational institutions allow students to resit exams, a recently proposed mathematical model suggests that this could lead to a dramatic reduction in study-time investment, especially in rational students. In the current study, we present a modification of this model in which we included some well-justified assumptions about learning and performance on multiple-choice tests, and we tested its predictions in two experiments in which participants were asked to invest fictional study time for a fictional exam. Consistent with our model, the prospect of a resit exam was found to promote lower investments of study time for a first exam and this effect was stronger for participants scoring higher on the cognitive reflection test. We also found that the negative effect of resit exams on study-time investment was attenuated when access to the resit was made uncertain by making it probabilistic or dependent on obtaining a minimal, non-passing grade for the first attempt. Taken together, these results suggest that offering students resit exams may compromise the achievement of learning goals, and they raise the more general implication that second chances promote risky behavior. [ABSTRACT FROM AUTHOR]

Increasingly consumption of healthy foods is advised to improve population health. Reasons people give for choosing one food over another suggest that non-sensory features like health aspects are appreciated as of lower importance than taste. However, many food choices are made in the absence of the actual perception of a food’s sensory properties, and therefore highly rely on previous experiences of similar consumptions stored in memory. In this study we assessed the differential strength of food associations implicitly stored in memory, using an associative priming paradigm. Participants (N = 30) were exposed to a forced-choice picture-categorization task, in which the food or non-food target images were primed with either non-sensory or sensory related words. We observed a smaller N400 amplitude at the parietal electrodes when categorizing food as compared to non-food images. While this effect was enhanced by the presentation of a food-related word prime during food trials, the primes had no effect in the non-food trials. More specifically, we found that sensory associations are stronger implicitly represented in memory as compared to non-sensory associations. Thus, this study highlights the neuronal mechanisms underlying previous observations that sensory associations are important features of food memory, and therefore a primary motive in food choice. [ABSTRACT FROM AUTHOR]

To investigate which neural correlates are associated with successful working memory performance, fMRI was recorded in healthy younger and older adults during performance on an n-back task with varying task demands. To identify functional networks supporting working memory processes, we used independent component analysis (ICA) decomposition of the fMRI data. Compared to younger adults, older adults showed a larger neural (BOLD) response in the more complex (2-back) than in the baseline (0-back) task condition, in the ventral lateral prefrontal cortex (VLPFC) and in the right fronto-parietal network (FPN). Our results indicated that a higher BOLD response in the VLPFC was associated with increased performance accuracy in older adults, in both the baseline and the more complex task condition. This ‘BOLD-performance’ relationship suggests that the neural correlates linked with successful performance in the older adults are not uniquely related to specific working memory processes present in the complex but not in the baseline task condition. Furthermore, the selective presence of this relationship in older but not in younger adults suggests that increased neural activity in the VLPFC serves a compensatory role in the aging brain which benefits task performance in the elderly. [ABSTRACT FROM AUTHOR]