N-back Research Articles

Neuroimaging features for cognitive fatigue and its recovery with VR intervention: An EEG microstates analysis.

Cognitive fatigue is mainly caused by enduring mental stress or monotonous work, impairing cognitive and physical performance. Natural scene exposure is a promising intervention for relieving cognitive fatigue, but the efficacy of virtual reality (VR) simulated natural scene exposure is unclear. We aimed to investigate the effect of VR natural scene on cognitive fatigue and further explored its underlying neurophysiological alterations with electroencephalogram (EEG) microstates analysis. Ten participants performed a 20-minute 1-back task before and after VR intervention while EEG was recorded (pre-task, post-task). Performance was measured with mean accuracy rate (MAR) and mean reaction time (MRT) of the continuous 1-back task. VR simulation of the Canal Town scene was utilized to alleviate cognitive fatigue caused by 1-back tasks. Four resting-state phases were identified: beginning, pre, post, and end phases. Post-task had a higher MAR and a lower MRT than pre-task. For pre-task, MAR was negatively correlated with trials, while MRT was positively correlated with trials. Four EEG microstates classes (A-D) were identified, and their temporal parameters (mean duration, time coverage and occurrence) and transition probabilities were calculated. After intervention, mean duration and time coverage of class B decreased, all parameters of class C increased, while all parameters of class D decreased. Transition probabilities between classes B and D decreased but increased between classes A and C. VR simulation of Canal Town scene is a potentially effective method to alleviate cognitive fatigue. Microstate is an electrophysiological trait characteristic of cognitive fatigue and might be used to indicate the effect of VR intervention.

External trigeminal nerve stimulation (eTNS) Exhibits relaxation effects in fatigue states following napping deprivation.

In the face of inevitable declines in alertness and fatigue resulting from sleep deprivation, effective countermeasures are essential for maintaining performance. External trigeminal nerve stimulation (eTNS) presents a potential avenue for regulating alertness by activating the locus coeruleus and reticular activating system. Here, we conducted a within-subject study with 66 habitual nappers, subjecting them to afternoon nap-deprivation and applying either 20-minute of 120Hz eTNS or sham stimulation. We compared participants' performance in PVT and N-back tasks, subjective fatigue level and alertness ratings, and changes in heart rate variability, cortisol, and salivary alpha-amylase before and after stimulation. The results revealed a significant decline in PVT and N-back tasks performance, along with increased subjective fatigue levels in the sham stimulation group. In contrast, the eTNS stimulation group maintained behavioral performance, with lower post-stimulation fatigue levels than sham group. After stimulation, the eTNS group exhibited decreased mean R-R interval and elevated LF/HF ratios, i.e., a shift in autonomic nervous system activity towards sympathetic dominance, and a significant reduction in cortisol levels, indicating a state of relaxation alleviating drowsiness. These findings suggested that 120Hz eTNS stimulation might induce a relaxing effect, and thereby alleviate fatigue while preserving alertness and cognitive performance.

Working Memory as the Focus of the Bilingual Effect in Executive Functions

The bilingual effect on executive functions (EFs) has garnered considerable attention, with most studies focusing on the visual domain and largely overlooking the auditory domain. Furthermore, research has predominantly concentrated on specific subcomponents of executive functions, with few studies systematically examining all three key subcomponents. This raises two important questions: (a) Is the bilingual effect specific to certain modalities (modality-specific), or a more general phenomenon (modality-general)? (b) Is the bilingual effect concentrated in a specific component of executive functions (process-specific), or does it extend to all three components (process-general)? To explore these questions, this study recruited monolingual Chinese and bilingual Chinese–English participants, using matched visual and auditory Stroop, N-back, and task-switching tasks to assess inhibitory control, working memory, and cognitive flexibility in both groups. The results showed that, after controlling for variables like intelligence, socioeconomic status, and age, bilingualism significantly predicted performance in both auditory and visual working memory tasks, explaining 34% and 19% of the variance, respectively. However, no evidence was found to support a bilingual effect in inhibitory control or cognitive flexibility. In conclusion, these results suggest that bilingual effects are not only process-specific (affecting only working memory) but also modality-general (providing advantages in both visual and auditory modalities).

Single and combined effects of environmental heat stress and physical exercise on thermoregulation, executive function, and cerebral oxygenation.

This study investigated the single and combined effects of environmental heat stress and physical exercise on executive function (EF) performance, prefrontal cortex oxygenation, thermoregulatory responses and subjective perceptions. Sixteen subjects participated in four experimental sessions: two under moderate environmental conditions (23°C), with and without physical exercise (R23, E23), and two under hot environmental conditions (35°C), with and without physical exercise (R35, E35). In each session, participants completed EF tasks before and after 1h of passive rest or 45min of moderate-intensity cycling followed by 15min of rest. We used Δresponse time (ΔRT) and Δaccuracy (ΔACC) of EF tasks to demonstrate changes from pre to post experiment. Additionally, changes in cerebral oxygenation during EF tasks were illustrated using the Δoxygenation difference. Heat stress alone increased core temperature (Tcore), mean skin temperature (Tskin), heart rate (HR), thermal sensation (TS), and rating of perceived exertion (RPE). Exercise in a hot environment further increased physiological indicators and RPE, but TS exhibited a different pattern, with lower TS in R35 compared to E35 during the second battery of executive function tests. Moreover, heat stress alone increased ΔRT for the More-Odd Shifting task and the Stroop task under incongruent conditions, while decreasing the Δoxygenation difference during the More-Odd Shifting task. ΔRT for the 2-back, More-Odd Shifting and Stroop tasks under incongruent conditions were lower in the E35 trial than in the R35 trial, whereas the Δoxygenation difference was higher in the E35 trial compared to the R35 trial. These findings indicate that environmental heat stress alone increases Tcore and Tskin, alters TS, and impairs EF performance by decreasing prefrontal cortex oxygenation. A 45-min moderate-intensity exercise combined with environmental heat stress enhances the increases in body temperatures but mitigates the detrimental effects of heat stress alone on EF performance by increasing prefrontal cortex oxygenation.

Study on exhaled volatile organic compounds identifying cognitive fatigue induced by N-back task in healthy young adults.

Cognitive fatigue in specific occupations may present a risk to personal safety. The study aimed to explore the characteristic volatile organic compounds (VOCs) in exhaled breath in response to cognitive fatigue, to provide a scientific basis for the non-invasive exhaled breath diagnostic techniques for cognitive fatigue assessing. Thirty healthy young adults were recruited and assigned to complete two 1.5-hour cognitive fatigue-inducing trials of the N-back task and one control trial of low emotion film watching of the same duration time. The Chalder Fatigue Scale was employed to assess the cognitive fatigue of the subjects before and after the induction and film watching. Exhaled VOCs were collected and detected using a Bio-VOC sampler and Thermal Desorption Gas Chromatography-Mass Spectroscopy method. The differences in exhaled VOCs between the pre- and post-induction and film watching was evaluated using either the paired t-test or the Wilcoxon signed-rank test. It was found that the scale scores of the task group (n = 50) significantly increased after the induction, whereas no such findings were observed in the control group (n = 10), indicating that the cognitive fatigue state of the task group was effectively induced through the performance of the N-back task. A total of 15 VOCs were identified in the exhaled breath samples of the task group. And only the level of isoprene changed significantly from 339.77 ± 162.21 μg/m³ to 604.18 ± 230.75 μg/m³ with the induction of cognitive fatigue. In contrast, the change of isoprene in the control group was not statistically significant. The study demonstrated that after inducing cognitive fatigue by N-back task in healthy young subjects, isoprene levels in exhaled breath increased significantly. It suggests that isoprene could be considered a characteristic volatile organic compound in exhaled breath associated with cognitive fatigue.

A tale of two ages: fluid reasoning as a predictor of working memory training efficacy in middle-aged and older adults

ABSTRACT Research on working memory (WM) training reveals significant variability in training effects, indicating that pretraining cognitive abilities might account for these differences. However, consensus on whether higher (magnification account) or lower (compensation account) pretraining abilities predict greater training effects remains elusive. Our study aimed to clarify the role of fluid reasoning in predicting training performance (i.e. training scores at each session) and gains on near transfer WM tasks. We conducted two studies: Study 1 focused on middle-aged adults (47–65 years) and Study 2 on older adults (65–83 years). Participants in both studies were randomly assigned to either adaptive n-back training or an active control group and have all completed three WM tasks before and after 20 training sessions – the trained n-back task and two structurally different untrained tasks. Generally, greater average training scores were found in individuals with higher fluid reasoning for both age groups, although this trend did not reach statistical significance in older adults. Similarly, higher fluid reasoning predicted greater training gains only in the sample of middle-aged adults. Further analysis showed that both, middle-aged and older participants in the training groups exhibited higher gains on the trained n-back task but not on two other WM tasks. Additionally, fluid reasoning predicted n-back gains in both the training and control group. Consistent with a growing body of research, our results show limited generalization of training effects across untrained tasks. It seems that factors beyond pretraining ability should be considered when explaining between-participant differences in training performance.

Effects of Dual-Site Anodal Transcranial Direct Current Stimulation on Attention, Decision-Making, and Working Memory during Sports Fatigue in Elite Soccer Athletes.

Sports fatigue in soccer athletes has been shown to decrease neural activity, impairing cognitive function and negatively affecting motor performance. Transcranial direct current stimulation (tDCS) can alter cortical excitability, augment synaptic plasticity, and enhance cognitive function. However, its potential to ameliorate cognitive impairment during sports fatigue remains largely unexplored. This study investigated the effect of dual-site tDCS targeting the dorsolateral prefrontal cortex (DLPFC) or primary motor cortex (M1) on attention, decision-making, and working memory in elite soccer athletes during sports fatigue. Sports fatigue was induced in 23 (non-goalkeeper) elite soccer athletes, who then participated in three counterbalanced intervention sessions: dual-site tDCS over the M1, dual-site tDCS over the DLPFC, and sham tDCS. Following tDCS, participants completed the Stroop, Iowa Gambling, and 2-back tasks. We found a significant improvement in Stroop task accuracy following dual-site anodal tDCS over the M1 compared with the sham intervention in the incongruent condition (p = 0.036). Net scores in the Iowa Gambling task during blocks 4 (p = 0.019) and 5 (p = 0.014) significantly decreased under dual-site tDCS targeting the DLPFC compared with the sham intervention. No differences in 2-back task performance were observed between sessions (all p > 0.05). We conclude that dual-site anodal tDCS applied to the M1 enhanced attention performance while tDCS targeting the DLPFC increased risk propensity in a decision-making task during sports fatigue in elite soccer athletes. However, dual-site anodal tDCS targeting either the M1 or DLPFC did not significantly influence working memory performance during sports fatigue in this population. These preliminary findings suggest that dual-site tDCS targeting the M1 has beneficial effects on attention performance, potentially informing future research on sports fatigue in athletes. No: NCT06594978. Registered 09 September, 2024; https://clinicaltrials.gov/search?cond=NCT06594978.

Dedifferentiation of caudate functional organization is linked to reduced D1 dopamine receptor availability and poorer memory function in aging

Abstract Age-related alterations in cortico-striatal function have been highlighted as an important determinant of declines in flexible, higher-order, cognition in older age. However, the mechanisms underlying such alterations remain poorly understood. Computational accounts propose age-related dopaminergic decreases to impoverish neural gain control, possibly contributing to reduced specificity of cortico-striatal circuits, that are modulated by dopamine, in older age. Using multi-modal neuroimaging data (fMRI, PET) from a large lifespan cohort (n = 180), we assessed the relationship between dopamine D1-like receptors (D1DRs) and cortico-striatal function during rest and an n-back working memory task. The results revealed gradual age-related decreases in the specificity of functional coupling between the centrolateral caudate and cortical association networks during both rest and working memory, which in turn was associated with poorer short and long-term memory performance with older age. Critically, reduced D1DR availability in the caudate and the prefrontal cortex predicted less differentiated caudate-cortical coupling across the lifespan, in part accounting for the age-related declines observed on this metric. These findings provide novel empirical evidence for a key role of dopamine in maintaining functional specialization of cortico-striatal circuits as individuals age, bridging with computational models of deficient catecholaminergic neuromodulation underpinning age-related dedifferentiation of brain function.

Psychometric characteristics of the n-back task: Construct validity across age and stimulus type, internal consistency, test-retest and alternate forms reliability

Abstract Age-related impairments are observed in a variety of cognitive constructs, including significant deteriorations in working memory (WM) performance. To measure the WM, the commonly used task in cognitive aging is the n-back. Despite its widespread use, however, its psychometric properties have not been sufficiently studied. Previous research has typically examined construct validity by correlating n-back task measures with other WM tasks and has primarily assessed reliability through test-retest, occasionally including split-half reliability. In this study, we comprehensively examined the psychometric properties of the n-back task by evaluating its construct validity across different age groups (younger and older adults) and stimulus types (verbal and non-verbal) and by assessing reliability through three methods: test-retest, split-half, and alternate forms. Our findings showed similar performance in verbal and non-verbal n-back tasks for both younger and older adults in terms of discrimination ability and reaction time. However, age-related differences favored younger adults, providing evidence for construct validity. In addition, the n-back measures were stable over time, consistent for two halves, and comparable for different forms, demonstrating task. This study provides the first evidence supporting the validity of the n-back task with regard to age and stimulus type, alongside its reliability. These findings have important implications for clinical research and practice, suggesting that the n-back task can be confidently utilized in neuropsychological assessments.

Effect of the restricted visual field on mental workload during automobile driving

This study investigated the limited visual field effects on mental workload (MWL) during automobile driving. A total of 12 participants drove a driving simulator (DS) with varying shielding levels in the DS display’s upper region while concurrently performing a 2-back task to control MWL. The subjective MWL increased as the shielding rate increased, and the 2-back task was added. However, eye movement parameters were not significantly affected by the shielding rate but were influenced by the 2-back task. Further, the study established that a one-class support vector machine could quantitatively evaluate MWL based on eye movement parameters. The decision boundary obtained through the one-class support vector machine detected an increase in MWL caused by shielding, and the estimated MWL was 16%–31% of that caused by the 2-back task. The results suggest that designers should prioritize adequate visual fields in cabin space design to lower MWL.

Multiple constraint network classification reveals functional brain networks distinguishing 0-back and 2-back task.

Working memory is associated with general intelligence and is crucial for performing complex cognitive tasks. Neuroimaging investigations have recognized that working memory is supported by a distribution of activity in regions across the entire brain. Identification of these regions has come primarily from general linear model analyses of statistical parametric maps to reveal brain regions whose activation is linearly related to working memory task conditions. This approach can fail to detect nonlinear task differences or differences reflected in distributed patterns of activity. In this study, we take advantage of the increased sensitivity of multivariate pattern analysis in a multiple-constraint deep learning classifier to analyze patterns of whole-brain blood oxygen level dependent (BOLD) activity in children performing two different conditions of the emotional n-back task. Regional (supervoxel) whole-brain activation patterns from functional imaging runs of 20 children were used to train a set of neural network classifiers to identify task category (0-back vs. 2-back) and activation co-occurrence probability, which encoded functional connectivity. These simultaneous constraints promote the discovery of coherent networks that contribute towards task performance in each memory load condition. Permutation analyses discovered the global activation patterns and interregional coactivations that distinguish memory load. Examination of model weights identified the brain regions most predictive of memory load and the functional networks integrating these regions. Community detection analyses identified functional networks integrating task-predictive regions and found distinct patterns of network activation for each task type. Comparisons to functional network literature suggest more focused attentional network activation during the 2-back task. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

Comparative Effects of Different Exercise Types on Cardiovascular Health and Executive Function in Sedentary Young Individuals.

The present study aimed to compare the impacts of different exercise types on cardiovascular health and executive function in sedentary young individuals, and to determine the associations between cardiovascular function and executive function (EF) after exercise. Sixty-three sedentary participants were randomly divided into high-intensity interval training (HIIT), moderate-intensity continuous training (MICT), resistance exercise (RE), and control groups. Macro- and microvascular endothelial function were assessed using brachial artery flow-mediated dilation and fingertip reactive hyperemia index, respectively. Arterial stiffness was evaluated through carotid-femoral pulse wave velocity, ankle-brachial index, and augmentation index. EF performance was evaluated using the Stroop and N-back tasks. Functional near-infrared spectroscopy was employed to measure cortical activation and real-time oxyhemoglobin concentration (Oxy-Hb) changes in different cerebral regions. Key circulating biomarkers for vascular and cognitive function, including BDNF, irisin, VEGF, IGF-1, and TNF-α, were measured using enzyme-linked immunosorbent assays. Eight weeks of HIIT, MICT, and RE effectively improved macro- and microvascular endothelial function while reducing arterial stiffness in sedentary young individuals. Furthermore, exercise-induced increase in BDNF level was correlated with enhanced macrovascular endothelial function, while increase in IGF-1 level was associated with enhanced microvascular endothelial function and reduced arterial stiffness. Notably, both HIIT and MICT, but not RE, efficiently enhanced Oxy-Hb level in certain brain regions, such as the FPA and DLPFC, leading to the improvement in EF performance. Exercise-induced increase in Oxy-Hb level and EF performance were correlated with enhanced BDNF level and endothelial function and reduced arterial stiffness. Our study demonstrated that 8 weeks of HIIT, MICT, and RE effectively improved endothelial function in both macro- and microvessels, and arterial stiffness among sedentary young individuals. However, HIIT and MICT, but not RE, notably increased blood oxygen level in the FPA and DLPFC brain regions and improved EF performance. Due to the efficiency and time-saving features of HIIT, the present study highlights HIIT as an effective exercise prescription for promoting vascular and EF in sedentary young individuals. Importantly, the observed improvements in cardiovascular function following exercise training is pivotal in improving EF, and elevated circulating levels of biomarkers like BDNF and IGF-1, induced by exercise, are involved in the regulatory mechanisms.

Temporal Unfolding of Spelling-to-sound Mappings in Visual (Non)word Recognition.

Behavioral research has shown that inconsistency in spelling-to-sound mappings slows visual word recognition and word naming. However, the time course of this effect remains underexplored. To address this, we asked skilled adult readers to perform a 1-back repetition detection task that did not explicitly involve phonological coding, in which we manipulated lexicality (high-frequency words vs. pseudowords) and sublexical spelling-to-sound consistency (treated as a dichotomous-consistent vs. inconsistent-and continuous dimension), while recording their brain electrical activity. The ERP results showed that the adult brain distinguishes between real and nonexistent words within 119-172 msec after stimulus onset (early N170), likely reflecting initial, rapid access to a primitive visuo-orthographic representation. The consistency of spelling-to-sound mappings exerted an effect shortly after the lexicality effect (172-270 msec; late N170), which percolated to the 353- to 475-msec range but only for real words. This suggests that, in expert readers, orthographic and phonological codes become available automatically and nearly simultaneously within the first 200 msec of the recognition process. We conclude that the early coupling of orthographic and phonological information plays a core role in visual word recognition by mature readers. Our findings support "quasiparallel" processing rather than strict cognitive seriality in early visual word recognition.

Neural correlates of olfactory working memory in the human brain.

Previous research has revealed that the insula, pallidum, thalamus, hippocampus, middle frontal gyrus, and supplementary motor area are activated during odor memory and that the performance of olfactory working memory is affected by the verbalization of odors. However, the neural mechanisms underlying olfactory working memory and the role of verbalization in olfactory working memory are not fully understood. Twenty-nine participants were enrolled in a study to complete olfactory and visual n-back tasks using high- and low-verbalizability stimuli while undergoing fMRI imaging. The behavioral results showed that the participants achieved greater accuracy in the visual rather than olfactory n-back task. We observed increased activation in the precentral gyrus, superior frontal gyrus, middle frontal gyrus, supplementary motor area, and inferior parietal gyrus during olfactory working memory. Interestingly, decreased activation was observed in the olfactory 2-back task versus the 0-back task. Moreover, the left angular gyrus and inferior parietal gyrus were more strongly activated during processing of olfactory working memory using high-verbalizability odors. In conclusion, olfactory working memory engages cross-modal regions to facilitate responses, is involved in the monitoring and manipulation of information during working memory, and boasts a unique activation pattern that is different from that of visual working memory. Semantic information supports the representation of odor information in the working memory system.

Impact of Different Auditory Environments on Task Performance and EEG Activity

Mental workload could affect human performance. An inappropriate workload level, whether too high or too low, leads to discomfort and decreased task performance. Auditory stimuli have been shown to act as an emotional medium to influence the workload. For example, the ‘Mozart effect’ has been shown to enhance performance in spatial reasoning tasks. However, the impact of auditory stimuli on task performance and brain activity remains unclear. This study examined the effects of three different environments—quiet, music, and white noise—on task performance and EEG activities. The N-back task was employed to induce mental workload, and the Psychomotor Vigilance Task assessed participants’ alertness. We proposed a novel, statistically-based method to construct the brain functional network, avoiding issues associated with subjective threshold selection. This method systematically analyzed the connectivity patterns under different environments. Our analysis revealed that white noise negatively affected participants, primarily impacting brain activity in high-frequency ranges. This study provided deeper insights into the relationship between auditory stimuli and mental workload, offering a robust framework for future research on mental workload regulation.

Inter-Network Effective Connectivity During Emotional Working Memory Task in two independent samples of young adults.

Effective connectivity (EC) analysis provides valuable insights into the directionality of neural interactions, crucial for understanding the mechanisms underlying cognitive and emotional regulation in depressive and anxiety disorders. This study examined EC within key neural networks during working memory (WM) and emotional regulation (ER) tasks in young adults, both healthy and seeking help from mental health professionals for emotional distress. Dynamic Causal Modeling (DCM) was employed to analyze EC in two independent samples (n=97 and n=94). Participants performed an emotional n-back task to assess EC across the Central Executive Network (CEN), Default Mode Network (DMN), Salience Network (SN), and Face Processing Network. Group-level Parametric Empirical Bayes (PEB) analyses were conducted to examine EC patterns, with sub-analyses comparing individuals with and without depression and anxiety. Consistent patterns of positive (posterior probability > 0.95) DMN→CEN and DMN→SN EC were observed in both samples, predominantly in Low and High WM conditions without ER. However, individuals without depressive or anxiety disorders exhibited a significantly greater number of preserved connections that were replicated across both samples. This study highlights the different patterns of DMN→CEN EC in conditions with High and Low WM loads with/without ER, suggesting that in higher WM loads with ER, the integration of the DMN with the CEN is reduced to facilitate successful cognitive task performance. The findings also suggest that DMN→CEN and DMN→SN EC are significantly reduced in depressive and anxiety disorders, highlighting this pattern of reduced EC as a potential neural marker of these disorders.

Predicting the Irrelevant: Neural Effects of Distractor Predictability Depend on Load.

Distraction is ubiquitous in human environments. Distracting input is often predictable, but we do not understand when or how humans can exploit this predictability. Here, we ask whether predictable distractors are able to reduce uncertainty in updating the internal predictive model. We show that utilising a predictable distractor identity is not fully automatic but in part depends on available resources. In an auditory spatial n-back task, listeners (n = 33) attended to spoken numbers presented to one ear and detected repeating items. Distracting numbers presented to the other ear either followed a predictable (i.e., repetitive) sequence or were unpredictable. We used electroencephalography (EEG) to uncover neural responses to predictable versus unpredictable auditory distractors, as well as their dependence on perceptual and cognitive load. Neurally, pairs of targets and unpredictable distractors induced a sign-reversed lateralisation of pre-stimulus alpha oscillations (~10 Hz) and larger amplitude of the stimulus-evoked P2 event-related potential component. Under low versus high memory load, distractor predictability increased the magnitude of the frontal negativity component. Behaviourally, predictable distractors under low task demands (i.e., good signal-to-noise ratio and low memory load) made participants adopt a less biased response strategy. We conclude that predictable distractors decrease uncertainty and reduce the need for updating the internal predictive model. In turn, unpredictable distractors might mislead proactive spatial attention orientation, elicit larger neural responses and put higher demand on memory.

Baseline gray matter volume associates with working memory performance after prefrontal transcranial direct current stimulation.

Working memory is crucial for daily life and is often impaired in neuropsychiatric conditions. Attempts to enhance it using transcranial direct current stimulation (tDCS) have shown mixed results, possibly due to large inter-individual variability. This study assessed whether baseline regional brain volume was associated with working memory performance following tDCS. Healthy participants were randomly assigned to three bilateral tDCS protocols (sham, 1.5 mA, and 3 mA) over the dorsolateral prefrontal cortex (dlPFC) (anode-left, cathode-right) for 20 minutes, in a within-subjects design with a 2-week interval, followed by emotional and non-emotional 3-back tasks. Baseline volumetric data were used to extract gray matter volumes of defined regions of interest; the dlPFC, the medial PFC (mPFC), and the posterior cingulate cortex (PCC) bilaterally. Data from thirty-nine participants (69.2 % female, mean age: 24.56 years) across 112 tDCS sessions were analyzed. Findings revealed no significant association between working memory performance post sham-tDCS and gray matter volume. However, larger baseline cortical volumes across all regions were associated with slower reaction times and lower accuracy for the non-emotional task at 1.5 mA, whereas non-significant results were observed at 3 mA. For the emotional task, only a significant association for reaction time after 3 mA and left dlPFC and right PCC were found. Findings highlight not only the association between individual baseline gray matter, but also the impact of methodological choices, such as current intensity and outcome, on the effect of tDCS. Future research should aim to further explore individual variability and methodological factors to deepen our understanding of the mechanisms underlying tDCS.

THE PHYSIOLOGIC COMPLEXITY OF PREFRONTAL OXYGENATION DYNAMICS IS ASSOCIATED WITH AGE AND COGNITIVE FUNCTION

Abstract The hemodynamics of prefrontal cortex (PFC) oxygenation are regulated by numerous elements over multiple temporal scales. The dynamics in the fluctuations of PFC oxygenation are thus complex. Age may alter the multiscale regulation of PFC oxygenation, leading to diminished physiologic complexity of this important regulatory process. We aimed to characterize the effects of age and cognitive demand on such complexity in younger and older adults and its relationship to cognitive performance. Twenty-four younger (aged 28±3 years) and 27 older adults (aged 78±6 years) completed this study. The oxygenation (HbO2) and deoxygenation (HHb) signals of the PFC were recorded using functional near-infrared-spectroscopy (fNIRS) during the n-back task of blank, identification-of-X (IdX), and 2-back conditions. We used multiscale entropy to quantify the HbO2 and HHb complexity of fNIRS. It was observed that older adults exhibited lower fNIRS complexity regardless of task condition (p=0.0005) and lower percent increase of complexity from blank (p=0.02) or IdX (p=0.01) to 2-back compared to younger. Both groups exhibited greater complexity during IdX and 2-back compared to blank condition (p< 0.02). Those with greater HbO2 complexity had greater 2-back accuracy (p=0.02~0.04). Older adults with greater fNIRS complexity had faster reaction times (β=-0.56~-0.6, p=0.009~0.02); while younger with lower complexity had faster reaction times (β=0.58~0.62, p=0.01~0.02). Participants with greater increase of fNIRS complexity from blank to 2-back had faster 2-back reaction time (β=-0.68~-0.49, p=0.001~0.03). The complexity of fNIRS-measured PFC oxygenation fluctuations may capture the influence of aging and task demands on the regulation of prefrontal hemodynamics involved in cognitive task execution.

Brain Functional Characteristics in Football Players During Motor-Cognitive Dual Task: Insights From fNIRS.

Long-term training enables professional athletes to develop concentrated and efficient neural network organizations for specific tasks. This study used functional near-infrared spectroscopy to investigate task performance, brain functional characteristics, and their relationships in footballers during sport-specific motor-cognitive processes. Twenty-four footballers (athlete group, with 18 remaining of good signal quality) and 20 non-footballers (control group, with 16 remaining) completed four tasks: a single task (trigger buttons corresponding to the appearance direction of teammates with kicking actions), an N-back direction task, a dual task, and an N-back digit task. Brain activation, functional connectivity (FC), and lateralization were calculated, and their correlation with behavioral indicators was analyzed. Results showed that reaction times were shorter in footballers across all tasks. The activation value in the right dorsolateral prefrontal cortex (DLPFC) decreased during dual task compared to the resting state in the athlete group. The activation values in all brain regions (except left primary sensory cortex in the single task), right DLPFC (dual task), and left premotor cortex & left supplementary motor area (left PMC & left SMA, digit task) were significantly lower in the athlete group than in the control group. Footballers exhibited higher interhemispheric FC during the direction and digit tasks, and greater leftward bias in the DLPFC during the dual task. The FC between left prefrontal cortex (PFC) -left PMC & left SMA and within the left PFC region was significantly positively correlated with accuracy during the dual task. Footballers showed better task performance with less impact from load, lower central energy consumption and higher sensory-motor network connectivity during task execution, indicating a more efficient state. Enhancing brain function and related networks may improve athletes' reactive abilities and performance.