Neural α Oscillations and Pupil Size Differentially Index Cognitive Demand under Competing Audiovisual Task Conditions.

Cognitive demand is thought to modulate two often used, but rarely combined, measures: pupil size and neural α (8-12 Hz) oscillatory power. However, it is unclear whether these two measures capture cognitive demand in a similar way under complex audiovisual-task conditions. Here we recorded pupil size and neural α power (using electroencephalography), while human participants of both sexes concurrently performed a visual multiple object-tracking task and an auditory gap detection task. Difficulties of the two tasks were manipulated independent of each other. Participants' performance decreased in accuracy and speed with increasing cognitive demand. Pupil size increased with increasing difficulty for both the auditory and the visual task. In contrast, α power showed diverging neural dynamics: parietal α power decreased with increasing difficulty in the visual task, but not with increasing difficulty in the auditory task. Furthermore, independent of task difficulty, within-participant trial-by-trial fluctuations in pupil size were negatively correlated with α power. Difficulty-induced changes in pupil size and α power, however, did not correlate, which is consistent with their different cognitive-demand sensitivities. Overall, the current study demonstrates that the dynamics of the neurophysiological indices of cognitive demand and associated effort are multifaceted and potentially modality-dependent under complex audiovisual-task conditions.SIGNIFICANCE STATEMENT Pupil size and oscillatory α power are associated with cognitive demand and effort, but their relative sensitivity under complex audiovisual-task conditions is unclear, as is the extent to which they share underlying mechanisms. Using an audiovisual dual-task paradigm, we show that pupil size increases with increasing cognitive demands for both audition and vision. In contrast, changes in oscillatory α power depend on the respective task demands: parietal α power decreases with visual demand but not with auditory task demand. Hence, pupil size and α power show different sensitivity to cognitive demands, perhaps suggesting partly different underlying neural mechanisms.

Regional brain activity and neural network changes in cognitive-motor dual-task interference: A functional near-infrared spectroscopy study.

Previous neuroimaging studies have reported dual-task interference (DTi) and deterioration of task performance in a cognitive-motor dual task (DT) compared to that in a single task (ST). Greater frontoparietal activity is a neural signature of DTi; nonetheless, the underlying mechanism of cortical network in DTi still remains unclear. This study aimed to investigate the regional brain activity and neural network changes during DTi induced by highly demanding cognitive-motor DT. Thirty-four right-handed healthy young adults performed the spiral-drawing task. They underwent a paced auditory serial addition test (PASAT) simultaneously or independently while their cortical activity was measured using functional near-infrared spectroscopy. Motor performance was determined using the balanced integration score (BIS), a balanced index of drawing speed and precision. The cognitive task of the PASAT was administered with two difficulty levels defined by 1 s (PASAT-1 s) and 2 s (PASAT-2 s) intervals, allowing for the serial addition of numbers. Cognitive performance was determined using the percentage of correct responses. These motor and cognitive performances were significantly reduced during DT, which combined a drawing and a cognitive task at either difficulty level, compared to those in the corresponding ST conditions. The DT conditions were also characterized by significantly increased activity in the right dorsolateral prefrontal cortex (DLPFC) compared to that in the ST conditions. Multivariate Granger causality (GC) analysis of cortical activity in the selected frontoparietal regions of interest further revealed selective top-down causal connectivity from the right DLPFC to the right inferior parietal cortex during DTs. Furthermore, changes in the frontoparietal GC connectivity strength between the PASAT-2 s DT and ST conditions significantly correlated negatively with changes in the percentage of correct responses. Therefore, DTi can occur even in cognitively proficient young adults, and the right DLPFC and frontoparietal network being crucial neural mechanisms underlying DTi. These findings provide new insights into DTi and its underlying neural mechanisms and have implications for the clinical utility of cognitive-motor DTs applied to clinical populations with cognitive decline, such as those with psychiatric and brain disorders.

Cortical activation and brain network efficiency during dual tasks: An fNIRS study.

OBJECTIVE: Dual task (DT) is a commonly used paradigm indicative of executive functions. Brain activities during DT walking is usually measured by portable functional near infrared spectroscopy (fNIRS). Previous studies focused on cortical activation in prefrontal cortex and overlooked other brain regions such as sensorimotor cortices. This study is aimed at investigating the modulations of cortical activation and brain network efficiency in multiple brain regions from single to dual tasks with different complexities and their relationships with DT performance. METHODS: Forty-two healthy adults [12 males; mean age: 27.7 (SD=6.5) years] participated in this study. Participants performed behavioral tasks with portable fNIRS simultaneous recording. There were three parts of behavioral tasks: cognitive tasks while standing (serial subtraction of 3's and 7's), walking alone and DT (walk while subtraction, including serial subtraction of 3's and 7's). Cognitive cost, walking cost and cost sum (i.e., sum of cognitive and walking costs) were calculated for DT. Cortical activation, local and global network efficiency were calculated for each task. RESULTS: The cognitive cost was greater and the walking cost was less during DT with subtraction 3's compared with 7's (P's = 0.032 and 0.019, respectively). Cortical activation and network efficiency were differentially modulated among single and dual tasks (P's < 0.05). Prefrontal activation during DT was positively correlated with DT costs, while network efficiency was negatively correlated with DT costs (P's < 0.05). CONCLUSIONS: Our results revealed prefrontal over-activation and reduced network efficiency in individuals with poor DT performance. Our findings suggest that reduced network efficiency could be a possible mechanism contributing to poor DT performance, which is accompanied by compensatory prefrontal over-activation.

Cognitive-exercise dual-task promotes cognitive function recovery in chronic cerebral ischemia male rats through regulating PI3K/Akt signaling pathway via inhibition of EphrinA3/EphA4.

Chronic cerebral ischemia (CCI) can lead to vascular cognitive impairment, but therapeutic options are limited. Cognitive-exercise dual-task (CEDT), as a potential rehabilitation intervention, can attenuate cognitive impairment. However, the related mechanisms remain unclear. In this study, 2-vessel occlusion (2-VO) in male SD rats was performed to establish the CCI model. The rats were treated with cognitive, exercise, or CEDT intervention for 21 days. The Morris water maze (MWM) test was used to assess cognitive ability. TUNEL staining was used to detect the neuronal apoptosis. Immunofluorescence, RT-qPCR and Western blot were used to detect the protein or mRNA levels of EphrinA3, EphA4, p-PI3K, and p-Akt. The results showed that CEDT could improve performance in the MWM test, reverse the increased expression of EphrinA3 and EphA4, and the reduced expression of p-PI3K and p-Akt in CCI rats, which was superior to exercise and cognitive interventions. In vitro, oxygenglucose deprivation (OGD) challenge of astrocytes and neuronal cells were used to mimic cerebral ischemia. Immunofluorescence assay revealed that the levels of MAP-2, p-PI3K, and p-Akt were reduced in EphrinA3 overexpressed cells after OGD stimulation. Finally, the knock-down of EphrinA3 by shRNA significantly promoted the recovery of cognitive function and activation of PI3K/Akt after CEDT treatment in CCI rats. In conclusion, our study suggests that CEDT promotes cognitive function recovery after CCI by regulating the signaling axis of EphrinA3/EphA4/PI3K/Akt.

Impaired dual-task gait in Parkinson's disease is associated with brain morphology changes.

In Parkinson's disease (PD), impaired gait and cognition affect daily activities, particularly in the more advanced stages of the disease. This study investigated the relationship between gait parameters, cognitive performance, and brain morphology in patients with early untreated PD. 64 drug-naive PD patients and 47 healthy controls (HC) participated in the study. Single- and dual-task gait (counting task) were examined using an expanded Timed Up & Go Test measured on a GaitRite walkway. Measurements included gait speed, stride length, and cadence. A brain morphometry analysis was performed on T1-weighted magnetic resonance (MR) images. In PD patients compared to HC, gait analysis revealed reduced speed (p < 0.001) and stride length (p < 0.001) in single-task gait, as well as greater dual-task cost (DTC) for speed (p = 0.007), stride length (p = 0.014) and cadence (p = 0.029). Based on the DTC measures in HC, PD patients were further divided into two subgroups with normal DTC (PD-nDTC) and abnormally increased DTC (PD-iDTC). For PD-nDTC, voxel-based morphometric correlation analysis revealed a positive correlation between a cluster in the left primary motor cortex and stride-length DTC (r = 0.57, p = 0.027). For PD-iDTC, a negative correlation was found between a cluster in the right lingual gyrus and the DTC for gait cadence (r=-0.35, pFWE = 0.018). No significant correlations were found in HC. The associations found between brain morphometry and gait performance with a concurrent cognitive task may represent the substrate for gait and cognitive impairment occurring since the early stages of PD.

Transcranial direct current stimulation facilitates backward walking training.

Backward walking training presents a great challenge to the physical and neural systems, which may result in an improvement in gait performance. Transcranial direct current electrical stimulation (tDCS), which can non-invasively enhance cortical activity, has been reported to strengthen corticomotor plasticity. We investigated whether excitatory tDCS over the primary motor cortex (M1) or the dorsolateral prefrontal cortex (DLPFC) enhances the effects of backward walking training in healthy participants. Thirty-six healthy participants (16 men and 20 women, mean age 21.3 ± 1.4 years) participated in this study. The participants were randomly assigned to one of the three tDCS groups (M1, DLPFC, and sham). They performed 5 min of backward walking training during 15 min of tDCS. We evaluated dual-task forward and backward walking performance before and after training. Both tDCS groups increased walking speed in the backward condition, but the DLPFC group increased the dual-task backward walking speed more than the M1 group. The M1 group showed decreased gait variability in dual-task backward walking, whereas the DLPFC group showed increased gait variability. Backward walking training combined with M1 stimulation may increase the backward walking speed by reducing gait variability. Backward walking training combined with DLPFC stimulation may prioritize walking speed over gait stability. Our results indicate that backward walking training combined with tDCS may be extended to other rehabilitation methods to improve gait performance.

Working memory load modulates anticipatory postural adjustments during step initiation.

Working memory (WM) can influence selective attention. However, the effect of WM load on postural standing tasks has been poorly understood, even though these tasks require attentional resources. The purpose of this study was to examine whether WM load would impact anticipatory postural adjustments (APAs) during step initiation. Sixteen healthy young adults performed stepping tasks alone or concurrently with a WM task in a dual-task design. The stepping tasks involved volitional stepping movements in response to visual stimuli and comprised of simple and choice reaction time tasks and the Flanker task which consisted of congruent and incongruent (INC) conditions. In the dual-task condition, subjects were required to memorize either one or six digits before each stepping trial. Incorrect weight transfer prior to foot-lift, termed APA errors, reaction time (RT), and foot-lift time were measured from the vertical force data. The results showed that APA error rate was significantly higher when memorizing six-digit than one-digit numerals in the INC condition. In addition, RT and foot-lift time were significantly longer in the INC condition compared to the other stepping conditions, while there was no significant effect of WM load on RT or foot-lift time. These findings suggest that high WM load reduces the cognitive resources needed for selective attention and decision making during step initiation.

Impact of distinct cognitive domains on gait variability in individuals with mild cognitive impairment and dementia.

BACKGROUND: Gait variability is a common feature in neurodegenerative diseases and has been linked to cognitive impairment. Despite this link, the influence of specific cognitive domains, such as memory, visual spatial skills, executive function, and verbal function on gait variability is not well-understood. OBJECTIVE: To investigate the predictive value of these specific cognitive domains on gait variability in people with mild cognitive impairment (MCI) and dementia during preferred and dual task walking. METHOD: One hundred and two participants with either MCI or dementia underwent a comprehensive cognitive assessment and completed preferred and dual-task walking trials on a pressure-sensing walkway. Gait variability was assessed using the PKMAS software. Lower extremity function was evaluated with a self-reported validated scale. RESULTS: Our findings indicate that only visual spatial abilities had a moderate predictive value on gait variability [F (1, 78) = 17.30, p < 0.01, r = 0.43], both in preferred pace walking (70% direct effect) and dual-task walking (90% direct effect) (p's < 0.05). Additionally, lower extremity functional skills had a significant indirect effect (30%) on gait variability in preferred walking contexts. CONCLUSION: For individuals diagnosed with MCI or dementia, increased gait variability may be driven by deficits in visual spatial processing. An increased understanding of the role of visual spatial processing in gait variability can aid in the assessment and management of individuals with MCI or dementia, potentially leading to targeted interventions to improve mobility and safety.

An ecological investigation of the capacity to follow simultaneous speech and preferential detection of ones' own name.

Many situations require focusing attention on one speaker, while monitoring the environment for potentially important information. Some have proposed that dividing attention among 2 speakers involves behavioral trade-offs, due to limited cognitive resources. However the severity of these trade-offs, particularly under ecologically-valid circumstances, is not well understood. We investigated the capacity to process simultaneous speech using a dual-task paradigm simulating task-demands and stimuli encountered in real-life. Participants listened to conversational narratives (Narrative Stream) and monitored a stream of announcements (Barista Stream), to detect when their order was called. We measured participants' performance, neural activity, and skin conductance as they engaged in this dual-task. Participants achieved extremely high dual-task accuracy, with no apparent behavioral trade-offs. Moreover, robust neural and physiological responses were observed for target-stimuli in the Barista Stream, alongside significant neural speech-tracking of the Narrative Stream. These results suggest that humans have substantial capacity to process simultaneous speech and do not suffer from insufficient processing resources, at least for this highly ecological task-combination and level of perceptual load. Results also confirmed the ecological validity of the advantage for detecting ones' own name at the behavioral, neural, and physiological level, highlighting the contribution of personal relevance when processing simultaneous speech.

Efficacy of a dual task protocol on neurophysiological and clinical outcomes in migraine: a randomized control trial.

The main aim of this study was to investigate the efficacy of a dual task protocol in people with episodic migraine with respect to both active exercises only and cognitive task only treatments, concerning some neurophysiological and clinical outcomes. A randomized control trial was adopted in people with episodic migraine without aura. Some neurophysiological and clinical outcomes were collected (t0): resting motor threshold (rMT), short intracortical inhibition (SICI) and facilitation (ICF), pressure pain threshold (PPT), trail making test (TMT), frontal assessment battery (FAB), headache-related disability (MIDAS) and headache parameters. Then, participants were randomized into three groups: active exercise only (n = 10), cognitive task only (n = 10) and dual task protocol (n = 10). After 3 months of each treatment and after 1-month follow-up the same neurophysiological and clinical outcomes were revaluated. A significant time x group effect was only found for the trapezius muscle (p = 0.012, pη2 = 0.210), suggesting that PPT increased significantly only in active exercise and dual task protocol groups. A significant time effect was found for rMT (p < 0.001, pη2 = 0.473), MIDAS (p < 0.001, pη2 = 0.426), TMT (p < 0.001, pη2 = 0.338) and FAB (p < 0.001, pη2 = 0.462). A repeated measures ANOVA for SICI at 3 ms highlighted a statistically significant time effect for the dual task group (p < 0.001, pη2 = 0.629), but not for the active exercises group (p = 0.565, pη2 = 0.061), and for the cognitive training (p = 0.357, pη2 = 0.108). The dual task protocol seems to have a more evident effect on both habituation and sensitization outcomes than the two monotherapies taken alone in people with migraine.

Relationship between Walking and Driving, and Cognitive Functioning Common to Both Modes of Mobility, in Healthy Older Adults.

INTRODUCTION: Driving and walking, the two main modes of mobility, require numerous common skills in the motor, sensory, and cognitive domains that deteriorate with age. The objective of this study was to investigate the relationship between walking and driving in healthy older drivers and to determine whether certain cognitive processes are involved in both modes of mobility. METHOD: Seventy-six older drivers from the Safe Move cohort were assessed in the following three domains: (1) cognition, using parts A and B of the Trail Making Test (TMT), the digit symbol substitution test (DSST), the Stroop test, and the Digit span; (2) gait, using a dual-task (DT) paradigm with a counting task; and (3) driving, assessed via a 40-50 min on-road test. Analyses were also performed on 2 subgroups: young-old (70-74 years old; n = 43) and old-old (≥75 years; n = 33). RESULTS: Four significant correlations were found across the whole sample between gait performance under DT conditions and driving scores. One correlation was also found in old-old adults. None were found in young-old adults. Furthermore, several cognitive measures were significantly correlated to both modes of mobility: TMT-A and B completion time in the whole sample, and DSST performance in the whole sample and old-old adults. DISCUSSION/CONCLUSION: Walking in complex conditions and on-road driving performance are closely related in healthy older drivers. Visuospatial attention, processing speed, and executive function are crucial and common cognitive processes to both modes of mobility in this population. Impairment in these cognitive functions should thus alert health professionals as it can quickly lead to mobility disorders, loss of autonomy and social isolation. Developing specific preventive programs and mobility support systems for healthy older adults is also crucial.

Effect of Explicit Prioritization on Dual Tasks During Standing and Walking in People With Neurologic and Neurocognitive Disorders: A Systematic Review and Meta-analysis.

OBJECTIVES: To examine the effectiveness of explicit task (ie, equal, motor or cognitive) prioritization during dual tasking (DT) in adults with neurologic and neurocognitive disorders (stroke, Parkinson disease [PD], multiple sclerosis, dementia, Alzheimer disease, and mild cognitive impairment). DATA SOURCE: A systematic search in 4 databases (PubMed, Web of Science, Embase, and Cochrane Central) yielded 1138 unique studies published up to 2023. STUDY SELECTION: Forty-one experimental studies were selected that assessed the effect of explicit prioritization instructions on both motor and cognitive performance during dual-tasks related to standing and walking in selected populations. Primary outcome measures were walking speed and response accuracy. Availability of data allowed us to perform a meta-analysis on 27 of the 41 articles by using inverse variance with a random effects model. DATA EXTRACTION: The data including design, subject characteristics, motor and cognitive tasks, prioritization, motor and cognitive outcomes, instructions, and key findings were extracted. Two assessors rated the selected studies for risk of bias and quality using the Quality Assessment Tools of the National Institutes of Health. DATA SYNTHESIS: This study examined 1535 adults who were asked to perform motor-cognitive DT in standing or walking, including 381 adults with stroke, 526 with PD, 617 with multiple sclerosis, 10 with dementia, 9 with Alzheimer disease, and 8 with mild cognitive impairment. During all prioritization instructions, participants slowed down during DT (standardized mean difference (SMD)equal=0.43; SMDmotor=0.78; SMDcognitive=0.69, P<.03) while maintaining similar response accuracy (SMDequal=0.12; SMDmotor=0.23; SMDcognitive=-.01, P>.05). However, considerable between-group heterogeneity was observed resulting in different motor and cognitive responses between pathologies. CONCLUSION: Motor prioritization was achieved in adults with PD and stroke, unlike adults with neurocognitive disorders who were negatively affected by any type DT prioritizing. The reported within-group heterogeneity revealed that effects of explicit task prioritization are dependent on motor and cognitive task complexity, and the type of instructions. Recommendations are provided to ensure accurate use of instructions during DT paradigms.

Effects of dual-task resistance exercise on cognition, mood, depression, functional fitness, and activities of daily living in older adults with cognitive impairment: a single-blinded, randomized controlled trial.

BACKGROUND: Regular exercise is emphasized for the improvement of functional capacity and independence of older adults. This study aimed to compare the effects of a dual-task resistance exercise program and resistance exercise on cognition, mood, depression, physical function, and activities of daily living (ADL) in older adults with cognitive impairment. METHODS: A total of 44 older adults participated in the study. Participants were randomly allocated to an experimental group (n = 22) performing a dual-task resistance exercise program for cognitive function improvement and a control group (n = 22) performing a resistance exercise program. Both groups performed the exercise for 40 min per session, three times a week, for 6 weeks (18 sessions). Cognition, mood, depression, functional fitness, and ADL were quantified before and after the intervention using the Mini-Mental State Examination (MMSE), profile of mood states (POMS), geriatric depression scale (GDS), senior fitness test (SFT), and Korean version of ADL, respectively. RESULTS: There was a significant time and group interaction on the MMSE (p = 0.044). There were no significant time and group interactions in the POMS, GDS, SFT, or ADL. Cognitive function (p < 0.001), mood (p < 0.001), depression (p < 0.001), functional fitness (p < 0.001), and ADL (p < 0.001) significantly improved after dual-task resistance exercise, and cognitive function (p < 0.001), mood (p < 0.001), depression (p < 0.001), functional fitness (p < 0.001), and ADL (p < 0.001) significantly improved after resistance exercise. CONCLUSIONS: Dual-task resistance exercise is more effective than resistance exercise in improving cognitive function in older adults with cognitive impairment. Both dual-task resistance exercise and resistance exercise improves mood, depression, functional fitness, and ADL after the intervention. We propose using dual-task resistance exercises for cognitive and physical health management in the older adults with cognitive impairment. TRIAL REGISTRATION: This study was registered with the Clinical Research Information Service (WHO International Clinical Trials Registry Platform) (Registration ID, KCT0005389; Registration date, 09/09/2020).

The effect of dual-task training on cognitive ability, physical function, and dual-task performance in people with dementia or mild cognitive impairment: A systematic review and meta-analysis.

OBJECTIVE: To summarize the effect of dual-task training on cognitive, physical function, and dual-task performance in people with mild cognitive impairment or dementia. DATA SOURCES: Embase, PEDro, PsycINFO, PubMed, CINAHL, The Cochrane Library, and a forward search conducted via Web of Science have been searched from inception to July 2023. REVIEW METHODS: Good-quality randomized controlled trials compared dual-task training with no/placebo intervention or single-task training among people with a primary diagnosis of mild cognitive impairment or dementia were included. The PEDro scale was used to evaluate the methodological quality of individual studies. The Grading of Recommendations, Assessment, Development and Evaluations system was adopted to appraise the quality of evidence for each outcome. RESULTS: Eighteen trials (1325 participants) were included, and 17 provided data for meta-analysis. Comparing with no intervention, dual-task training led to significant improvements on attention (mean difference (MD) = -20.66, 95%CI [-39.42, -1.90]), functional mobility (MD = -2.73; 95%CI [-3.98, -1.49]). Compared with single-task training, dual-task training had greater effects on overall cognitive function (standardized mean difference (SMD) = 0.29, 95%CI [0.09, 0.49]), balance (SMD = 0.78, 95%CI [0.40, 1.15]) and functional mobility (MD = -1.17; 95%CI [-1.77, -0.58]). Its effect on dual-task performance remains inconclusive due to the inconsistent results reported. CONCLUSION: Low- to moderate-quality evidence supports that dual-task training has beneficial effects on cognitive function and physical function in individuals with dementia or mild cognitive impairment. The optimal training protocol of dual-task training on cognitive and physical functions, and dual-task performance remains uncertain. Well-designed, randomized studies with large enough sample sizes are warranted.

Adding a sustained attention task to a physically demanding cycling exercise exacerbates neuromuscular fatigue and impairs cognitive performance in both normoxia and hypoxia.

PURPOSE: Both cognitive motor dual-tasks (CMDT) protocols and hypoxic environments have been associated with significant impairments in cognitive and physical performance. We aimed to determine the effects of hypoxia on cognitive performance and neuromuscular fatigue during a highly physically demanding CMDT. METHODS: Fifteen young adults completed a first session involving a cognitive task (CTLCOG) followed by cycling exercise (CTLEX) in normoxia. After that, they randomly participated in CMDT sessions in normoxia (DTNOR) and hypoxia (DTHYP). The physical exercise consisted of 20 min cycling at a "hard" perceived effort, and the cognitive task consisted of 15 min sustained attention to response time task (SART). Concurrent psycho-physiological measurements included: quadriceps neuromuscular fatigue (peripheral/central components from femoral nerve electrostimulation), prefrontal cortex (PFC) oxygenation by near-infrared spectroscopy, and perception of effort. RESULTS: SART performance significantly decreased in DTNOR (-15.7 ± 15.6%, P < 0.01) and DTHYP (-26.2 ± 16.0%, P < 0.01) compared to CTLCOG (-1.0 ± 17.7%, P = 0.61). Peripheral fatigue similarly increased across conditions, whereas the ability of the central nervous system to activate the working muscles was impaired similarly in DTNOR (-6.1 ± 5.9%, P < 0.001) and DTHYP (-5.4 ± 7.3%, P < 0.001) compared to CTLEX (-1.1 ± 0.2%, P = 0.52). Exercise-induced perception of effort was higher in DTHYP vs. DTNOR and in DTNOR vs. CTLEX. This was correlated with cognitive impairments in both normoxia and hypoxia. PFC deoxygenation was more pronounced in DTHYP compared to DTNOR and CTLEX. CONCLUSION: In conclusion, performing a sustained attention task together with physically challenging cycling exercise promotes central neuromuscular fatigue and impairs cognitive accuracy; the latter is particularly noticeable when the CMDT is performed in hypoxia.

The effects of acute normobaric hypoxia on standing balance while dual-tasking with and without visual input.

PURPOSE: To investigate the influence of acute normobaric hypoxia on standing balance under single and dual-task conditions, both with and without visual input. METHODS: 20 participants (7 female, 20-31 years old) stood on a force plate for 16, 90-s trials across four balance conditions: single-task (quiet stance) or dual-task (auditory Stroop test), with eyes open or closed. Trials were divided into four oxygen conditions where the fraction of inspired oxygen (FIO2) was manipulated (normoxia: 0.21 and normobaric hypoxia: 0.16, 0.145 and 0.13 FIO2) to simulate altitudes of 1100, 3,400, 4300, and 5200 m. Participants breathed each FIO2 for ~ 3 min before testing, which lasted an additional 7-8 min per oxygen condition. Cardiorespiratory measures included heart rate, peripheral blood oxygen saturation, and pressure of end tidal (PET) CO2 and O2. Center of pressure measures included total path length, 95% ellipse area, and anteroposterior and mediolateral velocity. Auditory Stroop test performance was measured as response accuracy and latency. RESULTS: Significant decreases in oxygen saturation and PETO2, and increased heart rate were observed between normoxia and normobaric hypoxia (P < 0.0001). Total path length was higher at 0.13 compared to 0.21 FIO2 for the eyes closed no Stoop test condition (P = 0.0197). No other significant differences were observed. CONCLUSION: These findings suggest that acute normobaric hypoxia has a minimal impact on standing balance and does not influence auditory Stroop test or dual-task performance. Further investigation with longer exposure is required to understand the impact and time course of normobaric hypoxia on standing balance.

Impact of process interference on memory encoding and retrieval processes in dual-task situations.

Dual-tasks at the memory encoding stage have been shown to decrease recall performance and impair concurrent task performance. In contrast, studies on the effect of dual-tasks at the memory retrieval stage observed mixed results. Which cognitive mechanisms are underlying this dual-task interference is still an unresolved question. In the present study, we investigated the influence of a concurrent reaction-time task on the performance in a long-term memory task in two experiments. In Experiment 1, participants performed an auditory-verbal free recall memory task and a visual-manual spatial Stroop task in a single or dual-task condition, either at the encoding or retrieval stage of the memory task. In Experiment 2, we examined the influence of processing conflicts in a concurrent RT task on memory encoding. Both experiments showed detrimental effects on recall accuracy and concurrent RT task performance in dual-task conditions at the encoding stage. Dual-task conditions at the retrieval stage led to a slowdown in recall latency and impaired concurrent RT task performance, but recall accuracy was maintained. In addition, we observed larger Stroop congruency effects in the dual-task conditions, indicating an increased processing conflict. However, in Experiment 2, we analyzed the effect of the processing conflict in a time-locked manner and could not find a significant influence on success of memory encoding. These findings suggest that processes in both tasks share the same limited capacity and are slowed down due to parallel processing, but we could not find evidence that this is further influenced by task-specific processing conflicts.

Prefrontal cortex activation while walking did not change but gait speed improved after a randomized physical therapy intervention.

BACKGROUND: Higher prefrontal cortex (PFC) activation while walking may indicate reduced gait automaticity. AIM: We examine whether PFC activation during walking improves after training in older adults at risk for mobility disability. METHODS: Forty-two adults aged ≥ 65 participated in a randomized clinical trial (NCT026637780) of a 12-week timing and coordination physical therapy intervention to improve walking (n = 20 intervention, n = 22 active control). PFC activation was measured by functional near-infrared spectroscopy (fNIRS) during four walking tasks over 15 m, each repeated 4 times: even surface walking, uneven surface walking, even dual-task, uneven dual-task; dual-task was reciting every other letter of the alphabet while walking. Gait speed and rate of correct letter generation were recorded. Linear mixed models tested between arm differences in change of fNIRS, gait speed, and letter generation from baseline to follow-up (12-week, 24-week, and 36-week). RESULTS: Intervention arms were similar in mean age (74.3 vs. 77.0) and baseline gait speed (0.96 vs. 0.93 m/s). Of 24 comparisons of between arm differences in the fNIRS signals, only two were significant which were not supported by differences at other follow-up times or on other tasks. Gait speed, particularly during dual-task conditions, and correct letter generation did improve post-intervention but improvements did not differ by arm. DISCUSSION AND CONCLUSIONS: After training, PFC activation during walking generally did not improve and did not differ by intervention arm. Improvements in gait speed without increased PFC activation may point toward more efficient neural control of walking.

Validity and reliability of a ruler drop test to measure dual-task reaction time, choice reaction time and discrimination reaction time.

BACKGROUND: The aim of this study was to determine the absolute and relative reliability of the Ruler Drop Test (RDT) for assessing dual-task, choice, and discrimination reaction time. In addition, the construct validity of the RDT is examined in comparison to the Deary-Liewald reaction time (DLRT). METHODS: Tests were administered by the same evaluator, one week apart. Intraclass Correlation Coefficient (ICC3.1) was used to measure relative reliability, and the standard error of measurement (SEM) and minimal detectable change (MDC95) were used to measure absolute reliability. Spearman correlation test was used to measure construct validity. RESULTS: The results showed that the relative reliability was good for the choice ruler drop (ICC = 0.81), moderate for the dual-task ruler drop test (ICC = 0.70) and discrimination ruler drop test (ICC = 0.72), and good for simple ruler drop test. However, the simple ruler drop test had poor reliability (ICC = 0.57). The RDT shows construct validity compared to the DLRT. CONCLUSION: We conclude that the RDT is a suitable instrument for measuring dual-task, choice and discrimination reaction time. Future studies should explore the reliability of these measures in other populations.

Effects of a dual-task activity on gait parameters of people with and without intellectual disabilities.

BACKGROUND: The main objective of this study was to evaluate gait parameters in people with intellectual disability (ID) and without intellectual disability (WID) in two different walking conditions [single task vs. dual task (DT)]. A secondary aim was to evaluate the dual-task cost (DTC) that the DT causes in each group. METHODS: A total of 119 participants joined in this study: 56 ID (30 men) and 63 WID (30 men). The OptoGait system was used to assess gait. In addition, Witty photocells were added to assess gait under the DT condition. RESULTS: Single support time was lower for participants with ID (P < 0.01), while double support time was higher (P < 0.05). All coefficients of variation for gait parameters were higher in participants with ID. Additionally, changes in gait were observed in both groups during the DT condition compared with the single-task condition. These changes were larger for participants with ID in step length, double support time and gait speed (P < 0.001), resulting in a higher DTC in these variables in the ID group (P < 0.01). CONCLUSIONS: Both groups reduced gait performance in the DT condition. However, greater gait variability occurred in the ID group. In addition, DTC was higher for the ID group in all variables analysed. Therefore, people with ID show worse gait performance during a DT than people WID.