Increased reaction times and reduced response preparation already starts at middle age

Neuromuscular fatigue and cognitive constraints independently modify lower extremity landing biomechanics in healthy and chronic ankle instability individuals

The purpose was to determine the impact of both cognitive constraint and neuromuscular fatigue on landing biomechanics in healthy and chronic ankle instability (CAI) participants. Twenty-three male volunteers (13 Control and 10 CAI) performed a single-leg landing task before and immediately after a fatiguing exercise with and without cognitive constraints. Ground Reaction Force (GRF) and Time to Stabilization (TTS) were determined at landing in vertical, anteroposterior (ap) and mediolateral (ml) axes using a force plate. Three-dimensional movements of the hip, knee and ankle were recorded during landing using a motion capture system. Exercise-induced fatigue decreased ankle plantar flexion and inversion and increased knee flexion. Neuromuscular fatigue decreased vertical GRF and increased ml GRF and ap TTS. Cognitive constraint decreased ankle internal rotation and increased knee and hip flexion during the flight phase of landing. Cognitive constraint increased ml GRF and TTS in all three axes. No interaction between factors (group, fatigue, cognitive) were observed. Fatigue and cognitive constraint induced greater knee and hip flexion, revealing higher proximal control during landing. Ankle kinematic suggests a protective strategy in response to fatigue and cognitive constraints. Finally, these two constraints impair dynamic stability that could increase the risk of ankle sprain.

Association between physical activity, body composition, and cognitive performance among female office workers

Regular physical activity can potentially prevent cognitive decline. While most studies focused on the general decline of the elderly and child and adolescent population, aging is a gradual process and cognitive decline can commence in middle age. Other than the middle-aged working population, gender-specific nuances are another overlooked area regarding the relationship between physical activity and cognitive performance. Therefore, this study examines the associations and benefits of maintaining regular physical activity habits with cognitive function and body composition in middle-aged female office workers. The results show that middle-aged females exhibited age-related declines in working memory, while no significant age-related changes are observed in reaction time and executive function. However, the regular exercise group demonstrates the ability to maintain their cognitive performance across age, unlike the sedentary group, who experiences declines in reaction time and executive function with age. Our findings highlight the significant impact of age on specific cognitive functions in middle-aged females and the positive influence of regular exercise on cognitive performance. Furthermore, this study demonstrates the potential of "the Brain Gym" App for efficient cognitive function assessment. The findings underscore the importance of regular exercise for cognitive well-being in middle-aged females and provide valuable insights into the relationship between body composition and cognitive function.

Need for cognition is associated with the interaction of reward and task-load on effort: A verification and extension study

Here, we work to provide nuance around the assumption that people will work for rewards. We examine whether individuals' inherent tendency to mobilize cognitive effort (need for cognition, NFC) moderates this effect. We re-analyzed our existing data to verify an effect reported by Sandra and Otto (2018) regarding the association between NFC and reward-induced cognitive effort expenditure, using a more ecological cognitive task design and adding a psychophysiological measure of effort. Specifically, distinct from their short time course visual task-switching paradigm, we used a relatively long course auditory comprehension task paradigm. We found that, consistent with the original study, increased cognitive effort in response to incentive reward depends on individual differences in cognitive motivation (need for cognition). We also found that, to observe consistent phenomena, different indices of effort (behavioral and psychophysiological) need to be considered when evaluating the relationship between the effort expenditure and cognitive motivation. Pupil dilation showed an advantage over reaction time in revealing mental effort mobilized over a prolonged cognitive task. Our results suggest that assessing cognitive motivation when planning a behavior-change program involving reward feedback for positive performance could help to optimize individuals' effort investment.

Impact of Repetitive Transcranial Magnetic Stimulation to the Cerebellum on Performance of a Ballistic Targeting Movement

This study aimed to investigate the effects of repetitive transcranial magnetic stimulation (rTMS) of the cerebellum on changes in motor performance during a series of repetitive ballistic-targeting tasks. Twenty-two healthy young adults (n = 12 in the active-rTMS group and n = 10 in the sham rTMS group) participated in this study. The participants sat on a chair in front of a monitor and fixed their right forearms to a manipulandum. They manipulated the handle with the flexion/extension of the wrist to move the bar on the monitor. Immediately after a beep sound was played, the participant moved the bar as quickly as possible to the target line. After the first 10 repetitions of the ballistic-targeting task, active or sham rTMS (1 Hz, 900 pulses) was applied to the right cerebellum. Subsequently, five sets of 100 repetitions of this task were conducted. Participants in the sham rTMS group showed improved reaction time, movement time, maximum velocity of movement, and targeting error after repetition. However, improvements were inhibited in the active-rTMS group. Low-frequency cerebellar rTMS may disrupt motor learning during repetitive ballistic-targeting tasks. This supports the hypothesis that the cerebellum contributes to motor learning and motor-error correction in ballistic-targeting movements.

Tennis expertise reduces costs in cognition but not in motor skills in a cognitive-motor dual-task condition

Dual-process theories predict performance reductions under dual-task situations (= situations where two tasks have to be processed and executed simultaneously), because limited cognitive resources have to be shared between concurrent tasks. Increases in expertise should reduce the attentional resources needed to perform a motor task, leading to reduced dual-task costs. The current studies investigated whether expert tennis players (performance ratings of 1 to 14 in the German system) show smaller costs compared to intermediate players (performance ratings of 15 to 23). Two studies assessed single- and dual-task performance in a within-subject design in the same tennis task, returning balls into a target field. Two different cognitive tasks were used, a 3-back working memory task in study 1, and a vocabulary-learning task (episodic memory) in study 2. As predicted, performance in both cognitive tasks was reduced during dual-tasking, while the accuracy of tennis returns remained stable under cognitive challenge. These findings indicate that skilled tennis players show a task-prioritization strategy in favor of the tennis task in a dual-task situation. In study 1, intermediate players showed higher overall dual-task costs than experts, but the group differences in dual-task costs did not reach significance in study 2. This may have been due to less pronounced expertise-differences between the groups in study 2. The findings replicate and extend previous expertise studies in sports to the domain of tennis. We argue that an athlete's ability to keep up cognitive and motor performances in challenging dual-task situations may be a valid indicator of skill level.

Cerebral Cortical Activity During Academic Stress Amongst Undergraduate Medical Students at Kampala International University (Uganda)

BACKGROUND

Stress among medical students is related to their academic lifespan; however, information on brain health among medical students from developing countries continues to be scarce. The objective of this study was to establish perceived academic stress levels, assess the ability to cope with stress, and investigate its effects on the visual reaction time (VRT), audio reaction time (ART), and tactile reaction time (TRT) in the somatosensory cortex among medical students of Uganda.

METHODS

This was a cross-sectional study conducted among preclinical (n = 88) and clinical (n = 96) undergraduate medical students at Kampala International University Western Campus. A standard Perceived Stress Scale (PSS) was used to categorize stress into low, moderate, and severe while the ability to cope with stress was categorized into below average, average, above average, and superior stresscoper (SS). Data on reaction time were acquired through VRT, ART, and TRT using the catch-a-ruler experiment, and this was analyzed using SPSS version 20.

RESULTS

This study shows that preclinical students are more stressed than clinical students (PSS prevalence for low stress = preclinical; clinical: 40, 60%). Moderate stress was 48.4 and 51.6% while high perceived stress was 75 and 25% among preclinical and clinical students. Among male and female students in preclinical years, higher TRT and VRT were found in clinical students showing that stress affects the tactile and visual cortical areas in the brain, although the VRT scores were only significantly (P = 0.0123) poor in male students than female students in biomedical sciences. Also, highly stressed individuals had higher TRT and ART and low VRT. SS had high VRT and ART and low TRT in preclinical students, demonstrating the importance of the visual cortex in stress plasticity. Multiple regression showed a close relationship between PSS, ability to cope with stress, age, and educational level (P < 0.05), demonstrating the importance of social and psychological support, especially in the biomedical sciences.

CONCLUSION

Preclinical students suffer more from stress and are poorer SS than clinical students. This strongly impairs their cortical regions in the brain, thus affecting their academic productivity.

TDCS effects on pointing task learning in young and old adults

Skill increase in motor performance can be defined as explicitly measuring task success but also via more implicit measures of movement kinematics. Even though these measures are often related, there is evidence that they represent distinct concepts of learning. In the present study, the effect of multiple tDCS-sessions on both explicit and implicit measures of learning are investigated in a pointing task in 30 young adults (YA) between 27.07 ± 3.8 years and 30 old adults (OA) between 67.97 years ± 5.3 years. We hypothesized, that OA would show slower explicit skill learning indicated by higher movement times/lower accuracy and slower implicit learning indicated by higher spatial variability but profit more from anodal tDCS compared with YA. We found age-related differences in movement time but not in accuracy or spatial variability. TDCS did not skill learning facilitate learning neither in explicit nor implicit parameters. However, contrary to our hypotheses, we found tDCS-associated higher accuracy only in YA but not in spatial variability. Taken together, our data shows limited overlapping of tDCS effects in explicit and implicit skill parameters. Furthermore, it supports the assumption that tDCS is capable of producing a performance-enhancing brain state at least for explicit skill acquisition.

Self-Reported Fatigue After Mild Traumatic Brain Injury Is Not Associated With Performance Fatigability During a Sustained Maximal Contraction

Patients with mild traumatic brain injury (mTBI) are frequently affected by fatigue. However, hardly any data is available on the fatigability of the motor system. We evaluated fatigue using the Fatigue Severity Scale (FSS) and Modified Fatigue Impact Scale (MFIS) questionnaires in 20 participants with mTBI (>3 months post injury; 8 females) and 20 age- and sex matched controls. Furthermore, index finger abduction force and electromyography of the first dorsal interosseous muscle of the right hand were measured during brief and sustained maximal voluntary contractions (MVC). Double pulse stimulation (100 Hz) was applied to the ulnar nerve to evoke doublet-forces before and after the sustained contraction. Seven superimposed twitches were evoked during the sustained MVC to quantify voluntary muscle activation. mTBI participants reported higher FSS scores (mTBI: 5.2 ± 0.8 SD vs. control: 2.8 ± 0.8 SD; P < 0.01). During the sustained MVC, force declined to similar levels in mTBI (30.0 ± 9.9% MVC) and control participants (32.7 ± 9.8% MVC, P = 0.37). The decline in doublet-forces after the sustained MVC (mTBI: to 37.2 ± 12.1 vs. control: to 41.4 ± 14.0% reference doublet, P = 0.32) and the superimposed twitches evoked during the sustained MVC (mTBI: median 9.3, range: 2.2-32.9 vs. control: median 10.3, range: 1.9-31.0% doublet_pre, P = 0.34) also did not differ between groups. Force decline was associated with decline in doublet-force (R ² = 0.50, P < 0.01) for both groups. Including a measure of voluntary muscle activation resulted in more explained variance for mTBI participants only. No associations between self-reported fatigue and force decline or voluntary muscle activation were found in mTBI participants. However, the physical subdomain of the MFIS was associated with the decline in doublet-force after the sustained MVC (R ² = 0.23, P = 0.04). These results indicate that after mTBI, increased levels of self-reported physical fatigue reflected increased fatigability due to changes in peripheral muscle properties, but not force decline or muscle activation. Additionally, muscle activation was more important to explain the decline in voluntary force (performance fatigability) after mTBI than in control participants.

Age-related alterations in reactive stepping following unexpected mediolateral perturbations during gait initiation

BACKGROUND

A common technique to regain stability following an unexpected perturbation is reactive stepping, aimed to control the accelerated center of mass (COM). Many older adults (OA) struggle to execute the fast, coordinated stepping strategy required to arrest COM movement within the base of support (BOS) during these unexpected events, likely due to age-related physiological declines. Recent ecological data also suggests that many falls in OA occur due to errors in transferring or shifting body weight during activities of daily living. The present study utilized gait initiation, which requires a coordinated transition from quiet stance to dynamic gait, as an example of one of these difficult transitional movements.

RESEARCH QUESTION

Our goal was to combine this inherently unstable task, gait initiation, with an unexpected mediolateral (ML) perturbation of the support surface to examine age-related changes in reactive stepping patterns during a novel transitional gait task.

METHODS

A total of 18 young adults (YA) and 16 OA (>65 years) performed 35 trials containing 10 unexpected ML perturbations of the support surface. To quantify age-related differences, we calculated step width, length, time and COM velocity in the first two steps following the perturbation.

RESULTS

We observed that, in general, OA walked slower and took shorter, faster steps (reducing time in single support) compared to YA. Following the perturbation, OA altered their stepping patterns by reducing their BOS (more narrow step width compared to YA), and required more than the two steps used by YA to complete the goal-directed task.

SIGNIFICANCE

These age-related changes are concerning as a multi-step recovery strategy has been previously associated with an elevated risk of falls in OA.

Microstructural Changes of the Human Brain from Early to Mid-Adulthood

Despite numerous studies on the microstructural changes of the human brain throughout life, we have indeed little direct knowledge about the changes from early to mid-adulthood. The aim of this study was to investigate the microstructural changes of the human brain from early to mid-adulthood. We performed two sets of analyses based on the diffusion tensor imaging (DTI) data of 111 adults aged 18–55 years. Specifically, we first correlated age with skeletonized fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) at global and regional level, and then estimated individuals’ ages based on each DTI metric using elastic net, a kind of multivariate pattern analysis (MVPA) method that aims at selecting the model that achieves the best trade-off between goodness of fit and model complexity. We observed statistically significant negative age-vs-FA correlations and relatively less changes of MD. The negative age-vs-FA correlations were associated with negative age-vs-AD and positive age-vs-RD correlations. Regional negative age-vs-FA correlations were observed in the bilateral genu of the corpus callosum (CCg), the corticospinal tract (CST), the fornix and several other tracts, and these negative correlations may indicate the earlier changes of the fibers with aging. In brain age estimation, the chronological-vs-estimated-age correlations based on FA, MD, AD and RD were R = 0.62, 0.44, 0.63 and 0.69 (P = 0.002, 0.008, 0.002 and 0.002 based on 500 permutations), respectively, and these results indicate that even the microstructural changes from early to mid-adulthood alone are sufficiently specific to decode individuals’ ages. Overall, the current results not only demonstrated statistically significant FA decreases from early to mid-adulthood and clarified the driving factors of the FA decreases (RD increases and AD decreases, in contrast to increases of both measures in late-adulthood), but highlighted the necessity of considering age effects in related studies.

The Age Effects on the Cognitive Processes of Intention-Based and Stimulus-Based Actions: An ERP Study

The functional decline in action among older adults is caused not only by physical weakness but also by cognitive decline. In this study, we aimed to compare the cognitive effects of age between intention-based and stimulus-based action modes electrophysiologically. Because age-related declines in cognitive function might proceed distinctly according to specific action modes and processes, four specific cognitive processes, action-effect binding, stimulus-response linkage, action-effect feedback control, and effect-action retrieval, were investigated. We recorded event-related potentials (ERPs) during a modified acquisition-test paradigm in young (mean age = 21, SD = 2) and old (mean age = 69, SD = 5) groups. A temporal bisection task and a movement pre-cuing task were used during the acquisition and test phases, respectively. Using ERP indices including readiness potential (RP), P3, N2 and contingent negative variation (CNV) to identify these four specific processes for the two action modes, we revealed the effects of age on each ERP index. The results showed similar patterns of waveforms but consistently decreasing amplitudes of all four ERP indices in the old age group compared with the young age group, which indicates not only generally declining functions of action preparation in older adults but also age effects specific to the action modes and processes that might otherwise be mixed together under confounding experimental conditions. Particularly, an interference effect indexed by the differences in the amplitudes of CNV between congruent and incongruent tasks was observed in the young age group, which is consistent with previous behavioral reports. However, this effect was absent in the old age group, indicating a specific age-related deficit in the effect-action retrieval process of intention-based action, which might be caused by an age-related deficit in associative memory. In sum, this study investigated the cognitive processes of two action modes from a developmental perspective and suggests the importance of adding associative memory training to interventions for older adults with the aim of improving intention-based action.

Cognitive Aging and Time Perception: Roles of Bayesian Optimization and Degeneracy

This review outlines the basic psychological and neurobiological processes associated with age-related distortions in timing and time perception in the hundredths of milliseconds-to-minutes range. The difficulty in separating indirect effects of impairments in attention and memory from direct effects on timing mechanisms is addressed. The main premise is that normal aging is commonly associated with increased noise and temporal uncertainty as a result of impairments in attention and memory as well as the possible reduction in the accuracy and precision of a central timing mechanism supported by dopamine-glutamate interactions in cortico-striatal circuits. Pertinent to these findings, potential interventions that may reduce the likelihood of observing age-related declines in timing are discussed. Bayesian optimization models are able to account for the adaptive changes observed in time perception by assuming that older adults are more likely to base their temporal judgments on statistical inferences derived from multiple trials than on a single trial's clock reading, which is more susceptible to distortion. We propose that the timing functions assigned to the age-sensitive fronto-striatal network can be subserved by other neural networks typically associated with finely-tuned perceptuo-motor adjustments, through degeneracy principles (different structures serving a common function).

Delayed grip relaxation and altered modulation of intracortical inhibition with aging

Grip relaxation is a voluntary action that requires an increase in short-interval intracortical inhibition (SICI) in healthy young adults, rather than a simple termination of excitatory drive. The way aging affects this voluntary inhibitory action and timing of grip relaxation is currently unknown. The objective of this study was to examine aging-related delays in grip relaxation and SICI modulation for the flexor digitorum superficialis muscle during grip relaxation. The main finding was that young adults increased SICI to relax their grips, whereas older adults did not increase SICI with a prolonged grip relaxation time (p < 0.05 for both SICI modulation and grip relaxation time). A secondary experiment showed that both young and older adults did not change H reflex excitability during grip relaxation. Our data suggest that grip relaxation is mediated by increased cortical inhibitory output in young adults, and aging-related impairment in increasing cortical inhibitory output may hamper timely cessation of muscle activity. Our data also suggest a lesser role of the spinal circuits in grip muscle relaxation. This knowledge may contribute to understanding of aging-related movement deterioration and development of interventions for improving modulation of SICI to improve muscle relaxation and movement coordination.

Age-related differences in muscle recruitment and reaction-time performance

Previously, we showed that prolonged reaction-time (RT) in older persons is related to increased antagonist muscle co-activation, occurring already before movement onset. Here, we studied whether a difference in temporal agonist and antagonist muscle activation exists between young and older persons during an RT-test. We studied Mm. Biceps (antagonist muscle) & Triceps (agonist muscle) Brachii activation time by sEMG in 60 young (26 ± 3 years) and 64 older (80 ± 6 years) community-dwelling subjects during a simple point-to-point RT-test (moving a finger using standardized elbow-extension from one pushbutton to another following a visual stimulus). RT was divided in pre-movement-time (PMT, time for stimulus processing) and movement-time (MT, time for motor response completion). Muscle activation time 1) following stimulus onset (PMAT) and 2) before movement onset (MAT) was calculated. PMAT for both muscles was significantly longer for the older subjects compared to the young (258 ± 53 ms versus 224 ± 37 ms, p=0.042 for Biceps and 280 ± 70 ms versus 218 ± 43 ms for Triceps, p<0.01). Longer agonist muscle PMAT was significantly related to worse PMT and RT in young (respectively r=0.76 & r=0.68, p<0.001) and elderly (respectively r=0.42 & r=0.40, p=0.001). In the older subjects we also found that the antagonist muscle activated significantly earlier than the agonist muscle (-22 ± 55 ms, p=0.003). We conclude that in older persons, besides the previously reported increased antagonist muscle co-activation, the muscle firing sequence is also profoundly altered. This is characterized by a delayed muscle activation following stimulus onset, and a significantly earlier recruitment of the antagonist muscle before movement onset.

Rumination and implicit avoidance following bereavement: an approach avoidance task investigation

BACKGROUND AND OBJECTIVES

Rumination, a risk factor in adjustment to bereavement, has often been considered a confrontation process. However, building on research on worry in generalized anxiety disorder (GAD) and rumination in post-traumatic stress disorder (PTSD), researchers recently developed the Rumination as Avoidance Hypothesis (RAH), which states that rumination after bereavement serves to avoid the reality of the loss. In the present study, RAH was tested by investigating if rumination is associated with implicit loss avoidance.

METHODS

An Approach Avoidance Task (AAT) was used to assess automatic behavior tendencies. Using a joystick, 71 persons who recently lost a first-degree relative (90.1% women), pulled stimuli toward themselves or pushed them away from themselves. Stimuli represented the loss (picture deceased + loss word), were loss-related but ambiguous (picture deceased + neutral word; picture stranger + loss word), or were non-loss-related (picture stranger + neutral word; puzzle picture + X's).

RESULTS

Participants who ruminated more were relatively faster in pushing loss stimuli away from themselves and slower in pulling loss stimuli towards themselves, implying more rumination was associated with stronger implicit loss avoidance. Effects were maintained after controlling for depressive or post-traumatic stress symptom levels, but not when controlling for prolonged grief symptom levels.

LIMITATIONS

Conjugally bereaved women were overrepresented in the sample, which limits generalizability of results. The study was correlational, precluding causal inferences.

CONCLUSIONS

In line with RAH, rumination was positively associated with loss avoidance. This may indicate that the application of exposure-based techniques can reduce rumination and loss-related psychopathology.

Reduced Dual-Task Performance in MS Patients Is Further Decreased by Muscle Fatigue

BACKGROUND

Multiple sclerosis (MS) can be accompanied by motor, cognitive, and sensory impairments. Additionally, MS patients often report fatigue as one of their most debilitating symptoms. It is, therefore, expected that MS patients will have difficulties in performing cognitive-motor dual tasks (DTs), especially in a fatiguing condition.

OBJECTIVE

To determine whether MS patients are more challenged by a DT than controls in a fatiguing and less-fatiguing condition and whether DT performance is associated with perceived fatigue.

METHODS

A group of 19 MS patients and 19 age-, sex-, and education-matched controls performed a cognitive task (2-choice reaction time task) separately or concurrent with a low-force or a high-force motor task (index finger abduction at 10% or 30% maximal voluntary contraction).

RESULTS

MS patients performed less well on a cognitive task than controls. Cognitive task performance under DT conditions decreased more for MS patients. Moreover, under high-force DT conditions, cognitive performance declined in both groups but to a larger degree for MS patients. Besides a decline in cognitive task performance, MS patients also showed a stronger decrease in motor performance under high-force DT conditions. DT costs were positively related to perceived fatigue as measured by questionnaires.

CONCLUSIONS

Compared with controls, MS patients performed less well on DTs as demonstrated by a reduction in both cognitive and motor performances. This performance decrease was stronger under fatiguing conditions and was related to the sense of fatigue of MS patients. These data illustrate problems that MS patients may encounter in daily life because of their fatigue.