Patterns of prefrontal cortical activity associated with attention-demanding and motor aspects of dual-task walking as measured with functional near-infrared spectroscopy.

IntroductionWalking with a prosthesis while performing secondary tasks increases demand on cognitive resources, compromising balance and gait. This study investigated effects of a secondary task on patterns of brain activity and temporospatial gait parameters in individuals using a prosthesis with or without a microprocessor-controlled prosthetic knee(MPK) and controls.MethodsA cross-sectional study with repeated measures was performed. Twenty-nine individuals with amputations and 16 controls were recruited. Functional near-infrared spectroscopy was used to evaluate changes in oxygenated and de-oxygenated haemoglobin in the prefrontal cortex and temporospatial variables during single-and dual-task walking.ResultsDifferences in brain activity were observed within the MPK-group and controls without changes in temporospatial parameters. The Trail-Walking test was associated with highest levels of brain activity in both groups. No differences were observed between single- and dual-task walking in the non-MPK-group (p > 0.05). The Non-MPK and the MPK-group recorded higher levels of brain activity than controls during single-task walking and poorer results on temporospatial variables compared to controls.ConclusionsFor the MPK-group and controls, introduction of a secondary task led to an increase in brain activity. This was not seen in the Non-MPK-group. Significant differences in brain activity were observed in the absence of changes in temporospatial parameters.

Neural trajectories of gait are not well established. We determined two distinct, clinically relevant neural trajectories, operationalized via functional near-infrared spectroscopy (fNIRS) HbO2 measures in the prefrontal cortex (PFC), under Single-Task-Walk (STW), and Dual-Task-Walk (DTW) conditions. Course trajectory assessed neural activity associated with attention during the course of a walking task; the second trajectory assessed neural activity associated with learning over repeated walking trials. Improved neural efficiency was defined as reduced PFC HbO2 after practice. Walking was assessed under STW and DTW conditions. fNIRS was utilized to quantify HbO2 in the PFC while walking. Burst measurement included three repeated trials for each experimental condition. The course of each walking task consisted of six consecutive segments. Eighty-three nondemented participants (mean age = 78.05 ± 6.37 years; %female = 49.5) were included. Stride velocity (estimate = -0.5259 cm/s, p = <.0001) and the rate of correct letter generation (log estimate of rate ratio = -0.0377, p < .0001) declined during the course of DTW. In contrast, stride velocity (estimate = 1.4577 cm/s, p < .0001) and the rate of correct letter generation (log estimate of rate ratio = 0.0578, p < .0001) improved over repeated DTW trials. Course and trial effects were not significant in STW. HbO2 increased during the course of DTW (estimate = 0.0454 μM, p < .0001) but declined over repeated trials (estimate = -0.1786 μM, p < .0001). HbO2 declined during the course of STW (estimate = -.0542 μM, p < .0001) but did not change significantly over repeated trials. We provided evidence for distinct attention (course) and learning (repeated trials) trajectories and their corresponding PFC activity. Findings suggest that learning and improved PFC efficiency were demonstrated in one experimental session involving repeated DTW trials.

Dual-task walking is a good paradigm to measure the walking ability of stroke patients in daily life. It allows for a better observation of brain activation under dual-task walking to assess the impact of the different tasks on the patient when combining with functional near-infrared spectroscopy (fNIRS). This review aims to summarize the cortical change of the prefrontal cortex (PFC) detected in single-task and dual-task walking in stroke patients. Six databases (Medline, Embase, PubMed, Web of Science, CINAHL, and Cochrane Library) were systematically searched for relevant studies, from inception to August 2022. Studies that measured the brain activation of single-task and dual-task walking in stroke patients were included. The main outcome of the study was PFC activity measured using fNIRS. In addition, a subgroup analysis was also performed for study characteristics based on HbO to analyze the different effects of disease duration and the type of dual task. Ten articles were included in the final review, and nine articles were included in the quantitative meta-analysis. The primary analysis showed more significant PFC activation in stroke patients performing dual-task walking than single-task walking (SMD = 0.340, P = 0.02, I 2 = 7.853%, 95% CI = 0.054-0.626). The secondary analysis showed a significant difference in PFC activation when performing dual-task walking and single-task walking in chronic patients (SMD = 0.369, P = 0.038, I 2 = 13.692%, 95% CI = 0.020-0.717), but not in subacute patients (SMD = 0.203, P = 0.419, I 2 = 0%, 95% CI = -0.289-0.696). In addition, performing walking combining serial subtraction (SMD = 0.516, P < 0.001, I 2 = 0%, 95% CI = 0.239-0.794), obstacle crossing (SMD = 0.564, P = 0.002, I 2 = 0%, 95% CI = 0.205-0.903), or a verbal task (SMD = 0.654, P = 0.009, I 2 = 0%, 95% CI = 0.164-1.137) had more PFC activation than single-task walking, while performing the n-back task did not show significant differentiation (SMD = 0.203, P = 0.419, I 2 = 0%, 95% CI = -0.289-0.696). Different dual-task paradigms produce different levels of dual-task interference in stroke patients with different disease durations, and it is important to choose the matching dual-task type in relation to the walking ability and cognitive ability of the patient, in order to better improve the assessment and training effects. https://www.crd.york.ac.uk/prospero/, identifier: CRD42022356699.

To determine whether brain activity over the prefrontal cortex measured in real time during walking predicts falls in high-functioning older adults. We examined166 older persons (mean age 75 years, 51% women) enrolled in a prospective aging study. High-functioning status defined as the absence of dementia or disability with normal gait diagnosed by study clinicians. The magnitude of task-related changes in oxygenated hemoglobin levels over the prefrontal cortex was measured with functional near-infrared spectroscopy during motor (walking at normal pace) and cognitive (reciting alternate letters of the alphabet) single tasks and a dual-task condition (walking while reciting alternate letters of the alphabet). Incident falls were prospectively assessed over a 50-month study period. Over a mean follow-up of 33.9 ± 11.9 months, 116 falls occurred. Higher levels of prefrontal cortical activation during the dual-task walking condition predicted falls (hazard ratio adjusted for age, sex, education, medical illnesses and general mental status 1.32, 95% confidence interval 1.03-1.70). Neither behavioral outcomes (velocity or letter rate) on the dual task nor brain activation patterns on the single tasks (normal walk or talk alone) predicted falls in this high-functioning sample. The results remained robust after accounting for multiple confounders and for cognitive status, slow gait, previous falls, and frailty. Prefrontal brain activity levels while performing a cognitively demanding walking condition predicted falls in high-functioning seniors. These findings implicate neurobiological processes early in the pathogenesis of falls.

Neural inefficiency is inferred when higher brain activations are associated with similar or worse performance. Improved neural efficiency is achieved when task-related brain activations are reduced after practice. No information is available on the effect of fear-of-falling (FOF) on brain activation during walking. We hypothesized that the presence of FOF would be associated with neural inefficiency and with a delay in improving neural efficiency during dual-task walking. Task conditions included single-task walk (STW), Alpha (cognitive interference), and dual-task walk (DTW). Functional near-infrared spectroscopy (fNIRS)-derived HbO2 in the prefrontal cortex (PFC) was used to quantify task-related changes in brain activation. Practice included three repeated counterbalanced trials for each task. Participants with FOF (n = 19; mean age = 79.84 ± 6.01years; %female = 68.42) and without FOF (n = 56; mean age = 76.73 ± 6.39years; %female = 44.64) were included. The presence of FOF was associated with slower stride velocity (estimate = - 12.354; p= 0.0154) and with greater increases in PFC HbO2 from STW to DTW (estimate = 0.303, p = 0.0009) and from Alpha to DTW (estimate = 0.387, p < 0.0001). Compared to controls, participants reporting FOF demonstrated an attenuated decline in PFC HbO2 from the first to the second DTW trials (estimate = 0.264; p = 0.0173). In contrast, compared to controls, participants with FOF demonstrated greater decline in Alpha PFC HbO2 from trial 1 to trial 2 (estimate = - 0.419, p < 0.0001) and from trial 1 to 3 (estimate = - 0.281, p = 0.0006). The change in PFC HbO2 over repeated STW trials was not significant and was not moderated by FOF status. The presence of FOF was associated with higher and inefficient PFC activation during DTW in older adults.

BackgroundWalking with a concurrent cognitive task (dual-task walking) can pose a challenge to some populations due to aging or neurodegenerative disease. These tasks require cognitive resources involving the prefrontal cortex and can be studied using functional near-infrared spectroscopy (fNIRS). An important step in understanding fNIRS measures during such walking tasks is validating that measures reflect the demands of the tasks and not confounding sources or movement artifacts. AimThis study aimed to investigate the validity of fNIRS measures of prefrontal cortex activity as an indicator of executive demand during usual walking (single-task) and dual-task walking against clinical and objective measures of motor behavior in young adults, older adults, and people with Parkinson’s disease (PD), by evaluating several validation hypotheses. MethodsIn total, 133 participants were recruited from younger adults (18–50 years, n = 42), older adults (≥60 years, n = 49) and people with PD (≥60 years, n = 42). Activity in the prefrontal cortex during walking with and without an auditory Stroop task was measured with fNIRS. A combined hemoglobin measure (correlation-based signal improvement, CBSI) was calculated for use in a region of interest analysis in the dorsolateral prefrontal cortex (dlPFC). Pre-registered hypotheses regarding convergent validity, discriminant validity and known group validity were tested. An exploratory analysis of different hemoglobin measures was also performed. ResultsIncreases in dlPFC activity were found from single- to dual-task walking in the younger adults group and from rest to single-task walking in the older adults and PD groups. In line with hypotheses, a positive relationship was found between between dlPFC activity during dual-task walking and dual-task cost in the younger adults group, as well as a positive relationship to step time variability during single-task walking and a negative relationship to walking speed during single-task walking in the PD group. However, several clinical and gait measures lacked a relationship with dlPFC activity. ConclusionThe fNIRS results point towards the CBSI measure of dlPFC activity being a valid measure of executive demand during both single and dual-task walking. Some relationships between clinical and gait measures and brain activity during walking need further investigation.

Dual-task costs of gait (variability) parameters are frequently used to probe the grade of automaticity of walking. However, recent studies reported contradicting dual-task costs for different gait variability measures within the same cohorts. The effects of a dual-task on the gait pattern are, thus, not fully understood. The aim of the current study was to analyze the different gait variability components ('Tolerance', 'Noise', and 'Covariation') during dual-task walking compared to single-task walking. In an experimental study, 21 young and healthy adults (11 males, 10 females, age: 24 ± 3years) were included. The participants completed three experimental conditions: (a) single-task walking, (b) dual-task walking (serial-seven subtractions), and (c) cognitive single task in sitting position. To analyze different gait variability components, we applied a method which distinguishes the three components: 'Tolerance', 'Noise', and 'Covariation' (TNC). To test for differences, we used the statistical parametric mapping method. Compared to single-task walking, the results depict lower gait variability of the result parameters during the dual-task condition at 0-15% (p = 0.010) and 94-100% (p = 0.040) of the stance phase and 0-63% (p < 0.001) during the swing phase. The decreased result parameter variability was due to less (sensorimotor) 'Noise' (stance: 2-100%, p < 0.001; swing: 2-59%, p < 0.001) during the dual-task walking condition. In further studies, the sources of the reduced unstructured (sensorimotor) noise in the dual-task condition should be analyzed to better understand the effect of a cognitive dual task on the gait pattern.

Over-recruitment of the prefrontal cortex (PFC) during complex walking conditions may reflect altered motor and cognitive performance in people with knee osteoarthritis (OA). Our objectives were (1) to assess PFC activation, and motor and cognitive performance, during single- and dual-task walking in people with knee OA and (2) to examine the association of PFC activation with the performance. Forty-eight people with symptomatic knee OA completed three tasks, (1) single-task walking (STW) (2) subtraction by 7 from a 3-digit number (S7), and (3) dual-task walking (DTW), a combination of STW and S7. Oxygenated hemoglobin concentration changes (ΔHbO2) in bilateral prefrontal cortex (PFC) were assessed using functional Near-Infrared Spectroscopy. Motor performance outcomes included gait speed, step duration variability, and stride length variability. Cognitive performance was assessed as the correct response rate during S7. We used repeated measures ANCOVA to compare the outcomes by tasks. Correlation and multiple linear regression analyses were used to determine the association between PFC activation and performance outcomes. PFC activation was higher during STW and DTW compared to S7 but not significantly different between STW and DTW. People with knee OA walked slower (d = 0.63) and had higher variability in step duration (d = 0.45) and stride length (d = 0.37) during DTW compared to STW. Greater activation in right ventrolateral PFC (R2 = 0.15) and left dorsomedial PFC (R2 = 0.12) were associated with lower step duration variability. When walking is challenged with a cognitive task, people with knee OA show deterioration of gait performance and no change in PFC activation.

To explore cognitive load in people with transfemoral amputations fitted with socket or bone-anchored prostheses by describing activity in the left and right dorsolateral prefrontal cortices during single- and dual-task walking. Cross-sectional pilot study. 8 socket prosthesis users and 8 bone-anchored prosthesis users. All were fitted with microprocessor-controlled prosthetic knees. Participants answered self-report questionnaires and performed gait tests during 1 single-task walking condition and 2 dual-task walking conditions. While walking, activity in the dorsolateral prefrontal cortex was measured using functional near-infrared spectroscopy. Cognitive load was investigated for each participant by exploring the relative concentration of oxygenated haemoglobin in the left and right dorsolateral prefrontal cortex. Symmetry of brain activity was investigated by calculating a laterality index. Self-report measures and basic gait variables did not show differences between the groups. No obvious between-group differences were observed in the relative concentration of oxygenated haemoglobin for any walking condition. There was a tendency towards more right-side brain activity for participants using a socket prosthesis during dual-task conditions. This pilot study did not identify substantial differences in cognitive load or lateralization between socket prosthesis users and bone-anchored prosthesis users.

Objective:Functional near-infrared spectroscopy (fNIRS) is a non-invasive functional neuroimaging method that takes advantage of the optical properties of hemoglobin to provide an indirect measure of brain activation via task-related relative changes in oxygenated hemoglobin (HbO). Its advantage over fMRI is that fNIRS is portable and can be used while walking and talking. In this study, we used fNIRS to measure brain activity in prefrontal and motor region of interests (ROIs) during single- and dual-task walking, with the goal of identifying neural correlates.Participants and Methods:Nineteen healthy young adults [mean age=25.4 (SD=4.6) years; 14 female] engaged in five tasks: standing single-task cognition (serial-3 subtraction); single-task walking at a self-selected comfortable speed on a 24.5m oval-shaped course (overground walking) and on a treadmill; and dual-task cognition+walking on the same overground course and treadmill (8 trials/condition: 20 seconds standing rest, 30 seconds task). Performance on the cognitive task was quantified as the number of correct subtractions, number of incorrect subtractions, number of self-corrected errors, and percent accuracy over the 8 trials. Walking speed (m/sec) was recorded for all walking conditions. fNIRS data were collected on a system consisting of 16 sources, 15 detectors, and 8 short-separation detectors in the following ROIs: right and left lateral frontal (RLF, LLF), right and left medial frontal (RMF, LMF), right and left medial superior frontal (RMSF, LMSF), and right and left motor (RM, LM). Lateral and medial refer to ROIs’ relative positions on lateral prefrontal cortex. fNIRS data were analyzed in Homer3 using a spline motion correction and the iterative weighted least squares method in the general linear model. Correlations between the cognitive/speed variables and ROI HbO data were applied using a Bonferroni adjustment for multiple comparisons.Results:Subjects with missing cognitive data were excluded from analyses, resulting in sample sizes of 18 for the single-task cognition, dual-task overground walking, and dual-task treadmill walking conditions. During dual-task overground walking, there was a significant positive correlation between walking speed and relative change in HbO in RMSF [r(18)=.51, p&lt;.05] and RM [r(18)=.53, p&lt;.05)]. There was a significant negative correlation between total number of correct subtractions and relative change in HbO in LMSF ([r(18)=-.75, p&lt;.05] and LM [r(18)=-.52, p&lt;.05] during dual-task overground walking. No other significant correlations were identified.Conclusions:These results indicate that there is lateralization of the cognitive and motor components of overground dual-task walking. The right hemisphere appears to be more active the faster people walk during the dual-task. By contrast, the left hemisphere appears to be less active when people are working faster on the cognitive task (i.e., serial-3 subtraction). The latter results suggest that automaticity of the cognitive task (i.e., more total correct subtractions) is related to decreased brain activity in the left hemisphere. Future research will investigate whether there is a change in cognitive automaticity over trials and if there are changes in lateralization patterns in neurodegenerative disorders that are known to differentially affect the hemispheres (e.g., Parkinson’s disease).

On Altered Patterns of Brain Activation in At-Risk Adolescents and Young Adults

Objective:Pain is a mechanism for attention disruption due, in part, to a shared reliance on the prefrontal cortex (PFC). Amongst older adults, the experience of pain is both prevalent and functionally impactful. Dual-task walking (DTW) paradigms are a useful means of assessing the impact of pain on attentional control and known to be sensitive to changes in the cortical hemodynamic response within the PFC. To date, however, few studies have utilized such paradigms to examine the impact of self-reported pain on attentional control via assessment of cognitive, gait and neuroimaging outcomes. Examining these associations would facilitate a better understanding of the ways in which pain may negatively impact neural efficiency, thereby increasing risk of adverse functional outcomes, in healthy aging.Participants and Methods:Study participants (N= 408; mean age = 76 ± 6.5ys; % female =55.4) were grouped into pain (n= 266) and no pain (n= 142) groups based upon their responses on the MOS-PSS and MOS-PES. These questionnaires were also used to assess self-reported levels of pain severity and interference amongst individuals with reported pain. Functional near-infrared spectroscopy was used to measure intraindividual variability (IIV) of the cortical hemodynamic response within the PFC during a DTW paradigm which consisted of Single-Task-Walk (STW), Cognitive Interference (Alpha), and Dual-Task-Walk (DTW) conditions. Participants walked along an electronic walkway and quantitative gait data were extracted in order to assess IIV in stride length during STW and DTW conditions. The rate of correct letter generation was used as a measure of cognitive accuracy during Alpha and DTW conditions. Linear mixed effects models (LMEMs) were used to examine the effects of perceived pain on neural and behavioral responses as well as on the change in these outcomes form single- to dual-task conditions. Stratified LMEMs were used to examine whether these associations differed by gender.Results:LMEMs revealed that perceived pain presence was associated with reduced IIV in PFC oxygenation (estimate = -0.032, p = 0.037) and reduced IIV in stride length in the DTW condition (estimate = -1.180, p = 0.006). High pain severity was associated with a greater increase in stride length IIV from STW to DTW (estimate = -1.301, p = 0.039). Stratified LMEMs revealed that the association between pain and neural IIV was significant in only males (estimate = -0.049, p = 0.037), while the association between pain and gait IIV was significant in only females (estimate = -1.712, p = .008).Conclusions:Study results suggest that self-reported pain over one month is associated with differential patterns of neural and behavioral responding amongst healthy, community-dwelling older adults. Furthermore, it appears that males are more susceptible to the neural effects of pain, while females are more susceptible to the behavioral effects under attention-demanding conditions. In this population, these patterns may reflect a tendency towards inefficient neural and behavioral modifications in response to perceived pain. These findings highlight the need for clinical use of routine pain assessments and, when appropriate, the implementation of timely and effective pain treatments in aging.

Cognitive impairment may present early in people with Parkinson's disease (PwPD), with deficits in executive function potentially impacting gait performance. Previous studies have investigated the association between dual-task walking and executive function in PwPD; however, the results were inconsistent, and the correlation between dual-task walking and subdomains of executive function has not been explored. This study aims to examine the correlation between dual-task walking and subdomains of executive function in PD and assess the predictive power of different subdomains of executive function on dual-task walking performance. This cross-sectional study included 30 PwPD. Gait was assessed under single-task walking, cognitive dual-task walking, and motor dual-task walking conditions. Executive function was evaluated using the Trail Making Test (TMT), Stroop Color and Word Test (SCWT), and Digit Span Test (DST). Correlation analyses (Pearson or Spearman, as appropriate) and linear regression analyses were used to examine the contribution of executive function subdomains to gait variables that showed significant correlations. Walking speeds under both dual-task conditions were moderately correlated with performance on the TMT Part A and the SCWT. In contrast, stride length during dual-task walking showed broader associations, demonstrating significant correlations with multiple executive function measures. Stepwise linear regression analysis revealed that the SCWT was the only significant predictor of walking speed under both dual-task conditions. For stride length during cognitive dual-task walking, the SCWT remained a significant predictor, while in the motor dual-task condition, both the SCWT and the Forward DST contributed significantly. Specifically, two regression models were significant for stride length during motor dual-task walking: Model 1 included only the SCWT, while Model 2 incorporated both the SCWT and Forward DST. Among dual-task cost outcomes, only the cost of stride length during cognitive dual-task walking was significantly correlated with TMT Part A; however, this association did not remain significant in subsequent regression analyses. This study indicates that, among various executive function assessments, the SCWT shows the strongest correlation with dual-task gait performance in PwPD. This suggests that inhibitory control plays a key role in regulating dual-task walking in individuals with PD.

Effect of a socıal defeat experıence on prefrontal actıvıty ın schızophrenıa

Evidence provides support for using functional near-infrared spectroscopy (fNIRS) to quantify brain activations, notably in the pre-frontal cortex (PFC), under different walking conditions. Dual-tasks that involve walking impose additional demands on attention resources relative to the single tasks, and Studies using fNIRS revealed increased HbO2 in the PFC in Dual-Task-Walk (DTW) compared to Single-Task-Walk (STW) conditions in several populations. Burst measurement within session, which involves repeated administration of the same task, affords evaluation of short-term practice effects on changes in walking performance and the efficiency of its underlying neural activation. Here, we examined the effects of task (STW vs. DTW) and burst measurement (three counter-balanced repeated trials of each task condition) on walking performance and fNIRS-derived HbO2 in the PFC in older adults with multiple sclerosis (n=80, %female=65%, mean age=64ys) and controls (n=79, %female=65, mean age=69ys). Participants were enrolled in an ongoing cohort study designed to determine cognitive and brain predictors of locomotion in older adults with MS. Results from linear mixed effects models (LMEMs) revealed: 1) higher fNIRS-derived HbO2 in DTW compared to STW (p&amp;lt;.01). 2) fNIRS-derived HbO2 levels declined over repeated trials, notably in DTW (p&amp;lt;.01). 3) gait velocity was slower in DTW compared to STW (p&amp;lt;.01). 4) gait velocity improved over repeated trials (p&amp;lt;.01). The combination of decline in fNIRS-derived HbO2 levels and faster walking over repeated trials under DTW suggests more efficient usage of brain resources to support attention-demanding locomotion in aging and neurological disease.