Associations between prefrontal cortex activation and H-reflex modulation during dual task gait

Adaptive gait responses to varying weight-bearing conditions: Inferences from gait dynamics and H-reflex magnitude

This study investigates the effects of varying loading conditions on excitability in neural pathways and gait dynamics. We focussed on evaluating the magnitude of the Hoffman reflex (H-reflex), a neurophysiological measure representing the capability to activate motor neurons and the timing and placement of the foot during walking. We hypothesized that weight manipulation would alter H-reflex magnitude, footfall and lower body kinematics. Twenty healthy participants were recruited and subjected to various weight-loading conditions. The H-reflex, evoked by stimulating the tibial nerve, was assessed from the dominant leg during walking. Gait was evaluated under five conditions: body weight, 20% and 40% additional body weight, and 20% and 40% reduced body weight (via a harness). Participants walked barefoot on a treadmill under each condition, and the timing of electrical stimulation was set during the stance phase shortly after the heel strike. Results show that different weight-loading conditions significantly impact the timing and placement of the foot and gait stability. Weight reduction led to a 25% decrease in double limb support time and an 11% narrowing of step width, while weight addition resulted in an increase of 9% in step width compared to body weight condition. Furthermore, swing time variability was higher for both the extreme weight conditions, while the H-reflex reduced to about 45% between the extreme conditions. Finally, the H-reflex showed significant main effects on variability of both stance and swing phases, indicating that muscle-motor excitability might serve as feedback for enhanced regulation of gait dynamics under challenging conditions.

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.

Neurophysiological and gait outcomes during a dual-task gait assessment in concussed adolescents

BACKGROUND

Gait deficits are common after concussion in adolescents. However, the neurophysiological underpinnings of these gait deficiencies are currently unknown. Thus, the goal of this study was to compare spatiotemporal gait metrics, prefrontal cortical activation, and neural efficiency between concussed adolescents several weeks from injury and uninjured adolescents during a dual-task gait assessment.

METHODS

Fifteen concussed (mean age[SD]: 17.4[0.6], 13 female, days since injury: 26.3[9.9]) and 17 uninjured adolescents (18.0[0.7], 10 female) completed a gait assessment with three conditions repeated thrice: single-task walking, single-task subtraction, and dual-task, which involved walking while completing a subtraction task simultaneously. Gait metrics were measured using an inertial sensor system. Prefrontal cortical activation was captured via functional near-infrared spectroscopy. Neural efficiency was calculated by relating gait metrics to prefrontal cortical activity. Differences between groups and conditions were examined, with corrections for multiple comparisons.

FINDINGS

There were no significant differences in gait metrics between groups. Compared to uninjured adolescents, concussed adolescents displayed significantly greater prefrontal cortical activation during the single-task subtraction (P = 0.01) and dual-task (P = 0.01) conditions with lower neural efficiency based on cadence (P = 0.02), gait cycle duration (P = 0.03), step duration (P = 0.03), and gait speed (P = 0.04) during the dual-task condition.

INTERPRETATION

Our findings suggest that several weeks after injury concussed adolescents demonstrate lower neural efficiency and display a cost to gait performance when cognitive demand is high, e.g., while multitasking, suggesting that the concussed adolescent brain is less able to compensate when attention is divided between two concurrent tasks.

Treadmill Walking Maintains Dual-task Gait Performance and Reduces Frontopolar Cortex Activation in Healthy Adults

Studies examining dual-task gait (DTG) have used varying conditions such as overground or treadmill walking, however it is not known whether brain activation patterns differ during these conditions. Therefore, this study compared oxyhaemoglobin (O2Hb) responses of the prefrontal cortex (PFC) during overground and treadmill walking. A total of 30 participants (14M/16F) were recruited in a randomized crossover study comparing overground and treadmill walking under single- and dual-task (STG and DTG) conditions. The DTG consisted of performing walking and cognitive (serial subtraction by 7's) tasks concurrently. A portable 24-channel functional near-infrared spectroscopy system was placed over the PFC, corresponding the left and right dorsolateral PFC and frontopolar cortices (DLPFC and FPC) during overground and treadmill STG and DTG. Results showed a reduction in gait speed during DTG compared to STG on overground but not treadmill walking, while cognitive performance was maintained during DTG on both overground and treadmill walking. A reduction in O2Hb was seen in the FPC during DTG compared to a cognitive task only, and on the treadmill compared to overground walking. Increased activation was seen in the left and right DLPFC during DTG but did not differ between treadmill and overground walking. Our results support the concept of improved gait efficiency during treadmill walking, indicated by the lack of change in STG and DTG performance and concomitant with a reduction in FPC activation. These findings suggest different neural strategies underpinning treadmill and overground walking, which should be considered when designing gait assessment and rehabilitation interventions.

Placebo effect on gait: a way to reduce the dual-task cost in older adults

The ability to perform two tasks simultaneously is essential for daily activities. In older adults, this ability is markedly reduced, as evidenced by the dual-task cost on gait. Preliminary evidences indicate that the dual-task cost can be influenced by different types of manipulations. Here, we explored the effectiveness of a new approach to reduce the dual-task cost, based on the placebo effect, a psychobiological phenomenon whereby a positive outcome follows the administration of an inert device thought to be effective. Thirty-five healthy older adults were asked to walk on a sensorized carpet (single-task condition) and to walk while counting backward (dual-task condition) in two sessions (pre-test and post-test). A placebo group, randomly selected, underwent sham transcranial direct current stimulation over the supraorbital areas between sessions, along with information about its positive effects on concentration and attention. A control group did not receive any intervention between sessions. The dual-task cost was significantly reduced in the placebo group at the post-test session compared to the pre-test for several gait parameters (Cohen's d > 1.43). At the post-test session, the dual-task cost was also lower in the placebo group than in the control group (d > 0.73). Cognitive (number of subtractions and number of errors) and subjective (perceived mental fatigability) variables remained stable across sessions. The reduced dual-task cost in the placebo group could indicate the ability to re-establish the allocation of attentional resources between tasks. These findings could contribute to the development of cognitive strategies that leverage positive expectations to boost motor control in older adults.

Left and Right Cortical Activity Arising from Preferred Walking Speed in Older Adults

Cortical activity and walking speed are known to decline with age and can lead to an increased risk of falls in the elderly. Despite age being a known contributor to this decline, individuals age at different rates. This study aimed to analyse left and right cortical activity changes in elderly adults regarding their walking speed. Cortical activation and gait data were obtained from 50 healthy older individuals. Participants were then grouped into a cluster based on their preferred walking speed (slow or fast). Analyses on the differences of cortical activation and gait parameters between groups were carried out. Within-subject analyses on left and right-hemispheric activation were also performed. Results showed that individuals with a slower preferred walking speed required a higher increase in cortical activity. Individuals in the fast cluster presented greater changes in cortical activation in the right hemisphere. This work demonstrates that categorizing older adults by age is not necessarily the most relevant method, and that cortical activity can be a good indicator of performance with respect to walking speed (linked to fall risk and frailty in the elderly). Future work may wish to explore how physical activity training influences cortical activation over time in the elderly.

The Characteristics of the Reduction of Interference Effect during Dual-Task Cognitive-Motor Training Compared to a Single Task Cognitive and Motor Training in Elderly: A Randomized Controlled Trial

Many studies have indicated a weakening in several areas of cognitive functioning associated with the normal ageing process. One of the methods supporting cognitive functions in older adults is dual-task training which is based on performing cognitive and motor exercises at the same time. The study aimed at examining the characteristics of dual-task training compared to single-task training in participants over 65 years of age. Sixty-five subjects took part in the study. They were randomly assigned to three groups: dual-task cognitive-motor training (CM), single-task cognitive training (CT), and single-task motor training (MT). The training program in all groups encompassed 4 weeks and consisted of three, 30-min meetings a week. Specialized software was designed for the study. The main indicators, such as orientation and planning time and the number of errors, were monitored during the whole training in all groups. The obtained results have shown that the dual-task training was associated with a significantly greater number of movement errors, but not with a longer task planning time compared to the single-task condition training. There was a decrease in the time needed to plan a path in the mazes by subjects training in the CM, CT, and MT groups. The results indicate that after each type of training, the number of errors and the time needed to plan the path decrease, despite the increasing difficulty of the tasks. The length of planning time was strongly correlated with the number of errors made by individuals in the CM group (r = 0.74, p = 0.04), compared to the ST group-for which the said correlation was not significant (r = 0.7, p = 0.06). The dual-task cognitive-motor training is more cognitively demanding compared to the single-task cognitive and motor training. It manifests in a greater number of errors, but it does not extend the orientation and planning time.

Experiment protocols for brain-body imaging of locomotion: A systematic review

Introduction

Human locomotion is affected by several factors, such as growth and aging, health conditions, and physical activity levels for maintaining overall health and well-being. Notably, impaired locomotion is a prevalent cause of disability, significantly impacting the quality of life of individuals. The uniqueness and high prevalence of human locomotion have led to a surge of research to develop experimental protocols for studying the brain substrates, muscle responses, and motion signatures associated with locomotion. However, from a technical perspective, reproducing locomotion experiments has been challenging due to the lack of standardized protocols and benchmarking tools, which impairs the evaluation of research quality and the validation of previous findings.

Methods

This paper addresses the challenges by conducting a systematic review of existing neuroimaging studies on human locomotion, focusing on the settings of experimental protocols, such as locomotion intensity, duration, distance, adopted brain imaging technologies, and corresponding brain activation patterns. Also, this study provides practical recommendations for future experiment protocols.

Results

The findings indicate that EEG is the preferred neuroimaging sensor for detecting brain activity patterns, compared to fMRI, fNIRS, and PET. Walking is the most studied human locomotion task, likely due to its fundamental nature and status as a reference task. In contrast, running has received little attention in research. Additionally, cycling on an ergometer at a speed of 60 rpm using fNIRS has provided some research basis. Dual-task walking tasks are typically used to observe changes in cognitive function. Moreover, research on locomotion has primarily focused on healthy individuals, as this is the scenario most closely resembling free-living activity in real-world environments.

Discussion

Finally, the paper outlines the standards and recommendations for setting up future experiment protocols based on the review findings. It discusses the impact of neurological and musculoskeletal factors, as well as the cognitive and locomotive demands, on the experiment design. It also considers the limitations imposed by the sensing techniques used, including the acceptable level of motion artifacts in brain-body imaging experiments and the effects of spatial and temporal resolutions on brain sensor performance. Additionally, various experiment protocol constraints that need to be addressed and analyzed are explained.

Multiarea Brain Activation and Gait Deterioration During a Cognitive and Motor Dual Task in Individuals With Parkinson Disease

BACKGROUND AND PURPOSE

In people with Parkinson disease (PD), gait performance deteriorating during dual-task walking has been noted in previous studies. However, the effects of different types of dual tasks on gait performance and brain activation are still unknown. The purpose of this study was to investigate cognitive and motor dual-task walking performance on multiarea brain activity in individuals with PD.

METHODS

Twenty-eight participants with PD were recruited and performed single walking (SW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT) at their self-selected speed. Gait performance including walking speed, stride length, stride time, swing cycle, temporal and spatial variability, and dual-task cost (DTC) was recorded. Brain activation of the prefrontal cortex (PFC), premotor cortex (PMC), and supplementary motor areas (SMA) were measured using functional near-infrared spectroscopy during walking.

RESULTS

Walking performance deteriorated upon performing a secondary task, especially the cognitive task. Also, a higher and more sustained activation in the PMC and SMA during WCT, as compared with the WMT and SW, in the late phase of walking was found. During WMT, however, the SMA and PMC did not show increased activation compared with during SW. Moreover, gait performance was negatively correlated with PMC and SMA activity during different walking tasks.

DISCUSSION AND CONCLUSIONS

Individuals with mild to moderate PD demonstrated gait deterioration during dual-task walking, especially during WCT. The SMA and PMC were further activated in individuals with PD when performing cognitive dual-task walking.Supplemental Digital Content is Available in the Text.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A383 ).

Effects of different exercise intensities on prefrontal activity during a dual task

The effects of physical exercise on cognitive tasks have been investigated. However, it is unclear how different exercise intensities affect the neural activity. In this study, we investigated the neural activity in the prefrontal cortex (PFC) by varying the exercise intensity while participants performed a dual task (DT). Twenty healthy young adults performed serial subtraction while driving a cycle ergometer. Exercise intensity was set to one of three levels: low, moderate, or high intensity. We did not find any significant change in PFC activity during DT under either the control (no exercise) or low-intensity conditions. In contrast, we observed a significant increase in PFC activity during DT under moderate- and high-intensity conditions. In addition, we observed complex hemodynamics after DT. PFC activity decreased from baseline after DT under the control condition, while it increased under the low-intensity condition. PFC activity remained higher than the baseline level after DT under the moderate-intensity condition but returned to baseline under the high-intensity condition. The results suggest that moderate-intensity exercise with a cognitive load effectively increases PFC activity, and low-intensity exercise may increase PFC activity when combined with a cognitive load.

Neuroergonomic assessment of developmental coordination disorder

Until recently, neural assessments of gross motor coordination could not reliably handle active tasks, particularly in realistic environments, and offered a narrow understanding of motor-cognition. By applying a comprehensive neuroergonomic approach using optical mobile neuroimaging, we probed the neural correlates of motor functioning in young people with Developmental Coordination Disorder (DCD), a motor-learning deficit affecting 5-6% of children with lifelong complications. Neural recordings using fNIRS were collected during active ambulatory behavioral task execution from 37 Typically Developed and 48 DCD Children who performed cognitive and physical tasks in both single and dual conditions. This is the first of its kind study targeting regions of prefrontal cortical dysfunction for identification of neuropathophysiology for DCD during realistic motor tasks and is one of the largest neuroimaging study (across all modalities) involving DCD. We demonstrated that DCD is a motor-cognitive disability, as gross motor /complex tasks revealed neuro-hemodynamic deficits and dysfunction within the right middle and superior frontal gyri of the prefrontal cortex through functional near infrared spectroscopy. Furthermore, by incorporating behavioral performance, decreased neural efficiency in these regions were revealed in children with DCD, specifically during motor tasks. Lastly, we provide a framework, evaluating disorder impact in ecologically valid contexts to identify when and for whom interventional approaches are most needed and open the door for precision therapies.

Age-related changes in the interference between cognitive task components and concurrent sensorimotor coordination

Continuous sensorimotor coordinations (CSCs) such as driving, walking, using control interfaces or maintaining the body's balance are often performed alongside concurrent cognitive tasks involving attention and executive function. A range of these task combinations show interference, particularly in older adults, but the timing, direction and reciprocity of interference is not yet understood at the level of the tasks' information-processing operations. This paper compares the chronometry of dual task interference between a visual oddball task and a continuous visuomanual tracking task performed by young and older adults. The oddball task's constituent operations were identified using electrophysiological correlates, and deviations in the tracking task reflected perturbations to state monitoring and adjustment characteristics of CSC tasks. Despite instructions to give equal priority to both tasks, older participants maintained a high level of resourcing of the oddball task when dual tasking whereas young participants reduced resourcing to accommodate the demands of the tracking task. Older participants had a longer period of tracking inaccuracy during the executive function component of the oddball task, and unlike in young participants, this decrement was also observed when the stimulus was not a target and the executive function of updating the target tally was not required. These detailed chronometric results clarify that age-related amplification of CSC-cognitive interference are largely due to greater inflexibility in task prioritization. Prioritization of the cognitive task over the CSC in this type of dual tasking may have safety implications in everyday task settings.

Association of executive function capacity with gait motor imagery ability and PFC activity: An fNIRS study

Individual differences exist in gait motor imagery ability. However, little is known about the underlying neural mechanisms. We previously conducted a study using functional near-infrared spectroscopy (fNIRS), which showed that participants who overestimated mental walking times to a greater degree exhibited greater activation in the right prefrontal cortex (PFC). The PFC is implicated in executive functions (EFs), including working memory (WM). Thus, this study investigated whether individual differences in EF capacity are associated with gait motor imagery ability and PFC activity. Thirty volunteers participated (mean age: 21.7 ± 1.8 years) in the study. Their EF capacity was assessed by the Trail Making Test - Part B (TMT-B). We measured the accuracy of gait motor imagery and PFC activity during mental walking using fNIRS, while changing task difficulty by varying the path width. The results showed that the overestimation of mental walking time over actual walking time and right PFC activity increased with an increase in the TMT-B times. These results suggest that the EF capacity, including WM, is strongly associated with gait motor imagery ability and right PFC activity. The brain network that includes the right PFC may play an important role in the maintenance and manipulation of gait motor imagery.

Changes in Cortical Activity during Preferred and Fast Speed Walking under Single- and Dual-Tasks in the Young-Old and Old-Old Elderly

In the elderly, walking while simultaneously engaging in other activities becomes more difficult. This study aimed to examine the changes in cortical activity during walking with aging. We try to reveal the effects of an additional task and increased walking speed on cortical activation in the young-old and the old-old elderly. Twenty-seven young-old (70.2 ± 3.0 years) and 23 old-old (78.0 ± 2.3 years) participated in this study. Each subject completed four walking tasks on the treadmill, a 2 × 2 design; two single-task (ST) walking conditions with self-selected walking speed (SSWS) and fast walking speed (FWS), and two dual-task (DT) walking conditions with SSWS and FWS. Functional near-infrared spectroscopy was applied for measurement of cerebral oxyhemoglobin (oxyHb) concentration during walking. Cortical activities were increased during DT conditions compared with ST conditions but decreased during the FWS compared with the SSWS on the primary leg motor cortex, supplementary motor area, and dorsolateral prefrontal cortex in both the young-old and the old-old. These oxyHb concentration changes were significantly less prominent in the old-old than in the young-old. This study demonstrated that changes in cortical activity during dual-task walking are lower in the old-old than in the young-old, reflecting the reduced adaptive plasticity with severe aging.

Prefrontal Cortical Activity During Preferred and Fast Walking in Young and Older Adults: An fNIRS Study

Age-related changes may affect the performance during fast walking speed. Although, several studies have been focused on the contribution of the prefrontal cortex (PFC) during challenging walking tasks, the neural mechanism underling fast walking speed in older people remain poorly understood. Therefore, the aim of this study was to investigate the influence of aging on PFC activity during overground walking at preferred and fast speeds. Twenty-five older adults (67.37 ± 5.31 years) and 24 young adults (22.70 ± 1.30 years) walked overground in two conditions: preferred speed and fast walking speed. Five trials were performed for each condition. A wireless functional near-infrared spectroscopy (fNIRS) system measured PFC activity. Gait parameters were evaluated using the GAITRite system. Overall, older adults presented higher PFC activity than young adults in both conditions. Speed-related change in PFC activity was observed for older adults, but not for young adults. Older adults significantly increased activity in the left PFC from the preferred to fast walking condition whereas young adults had similar levels of PFC activity across conditions. Our findings suggest that older adults need to recruit additional prefrontal cognitive resources to control walking, indicating a compensatory mechanism. In addition, left PFC seems to be involved in the modulation of gait speed in older adults.

Influence of Different Dual-Task Conditions During Straight or Curved Walking on Gait Performance of Physically Active Older Women With Cognitive Decline

Real-world walking requires shifting attention from different cognitive demands to adapt gait. This study aims to evaluate the effect of dual tasking on spatiotemporal gait parameters of older adults. Participants were asked to perform a primary complex single-walking task, consisting of a fast-paced linear and a curved gait. Primary task was performed separately and simultaneously with different motor and cognitive secondary tasks. Spatiotemporal gait parameters, walk ratio, and walk stability ratio were measured. Apart from stride length, which stood relatively unchanged, gait speed and cadence were strongly affected by cognitive dual tasking. Cadence seems to be the most impacted by dual tasking during curved gait as it combines challenges of both primary and secondary tasks. Also, during curved phase, walking ratio was significantly lower and stability ratio was greater demonstrating that participants adopted a cautious gait where maintenance of stability took preference over efficiency.

Brain Activation Changes While Walking in Adults with and without Neurological Disease: Systematic Review and Meta-Analysis of Functional Near-Infrared Spectroscopy Studies

(1) Functional near-infrared spectroscopy (fNIRS) provides a useful tool for monitoring brain activation changes while walking in adults with neurological disorders. When combined with dual task walking paradigms, fNIRS allows for changes in brain activation to be monitored when individuals concurrently attend to multiple tasks. However, differences in dual task paradigms, baseline, and coverage of cortical areas, presents uncertainty in the interpretation of the overarching findings. (2) Methods: By conducting a systematic review of 35 studies and meta-analysis of 75 effect sizes from 17 studies on adults with or without neurological disorders, we show that the performance of obstacle walking, serial subtraction and letter generation tasks while walking result in significant increases in brain activation in the prefrontal cortex relative to standing or walking baselines. (3) Results: Overall, we find that letter generation tasks have the largest brain activation effect sizes relative to walking, and that significant differences between dual task and single task gait are seen in persons with multiple sclerosis and stroke. (4) Conclusions: Older adults with neurological disease generally showed increased brain activation suggesting use of more attentional resources during dual task walking, which could lead to increased fall risk and mobility impairments. PROSPERO ID: 235228.

Measuring the Cognitive Workload During Dual-Task Walking in Young Adults: A Combination of Neurophysiological and Subjective Measures

Background: Walking while performing a secondary task (dual-task (DT) walking) increases cognitive workload in young adults. To date, few studies have used neurophysiological measures in combination to subjective measures to assess cognitive workload during a walking task. This combined approach can provide more insights into the amount of cognitive resources in relation with the perceived mental effort involving in a walking task.

Research Question: The objective was to examine cognitive workload in young adults during walking conditions varying in complexity.

Methods: Twenty-five young adults (mean = 24.4 ± 5.4) performed four conditions: (1) usual walking, (2) simple DT walking, (3) complex DT walking and (4) standing while subtracting. During the walking task, mean speed, cadence, stride time, stride length, and their respective coefficient of variation (CV) were recorded. Cognitive workload will be measured through changes in oxy- and deoxy-hemoglobin (ΔHbO₂ and ΔHbR) during walking in the dorsolateral prefrontal cortex (DLPFC) and perceived mental demand score from NASA-TLX questionnaire.

Results: In young adults, ΔHbO₂ in the DLPFC increased from usual walking to both DT walking conditions and standing while subtracting condition. ΔHbO₂ did not differ between the simple and complex DT and between the complex DT and standing while subtracting condition. Perceived mental demand gradually increased with walking task complexity. As expected, all mean values of gait parameters were altered according to task complexity. CV of speed, cadence and stride time were significantly higher during DT walking conditions than during usual walking whereas CV of stride length was only higher during complex DT walking than during usual walking.

Significance: Young adults had greater cognitive workload in the two DT walking conditions compared to usual walking. However, only the mental demand score from NASA-TLX questionnaire discriminated simple from complex DT walking. Subjective measure provides complementary information to objective one on changes in cognitive workload during challenging walking tasks in young adults. These results may be useful to improve our understanding of cognitive workload during walking.

A consensus guide to using functional near-infrared spectroscopy in posture and gait research

BACKGROUND

Functional near-infrared spectroscopy (fNIRS) is increasingly used in the field of posture and gait to investigate patterns of cortical brain activation while people move freely. fNIRS methods, analysis and reporting of data vary greatly across studies which in turn can limit the replication of research, interpretation of findings and comparison across works.

RESEARCH QUESTION AND METHODS

Considering these issues, we propose a set of practical recommendations for the conduct and reporting of fNIRS studies in posture and gait, acknowledging specific challenges related to clinical groups with posture and gait disorders.

RESULTS

Our paper is organized around three main sections: 1) hardware set up and study protocols, 2) artefact removal and data processing and, 3) outcome measures, validity and reliability; it is supplemented with a detailed checklist.

SIGNIFICANCE

This paper was written by a core group of members of the International Society for Posture and Gait Research and posture and gait researchers, all experienced in fNIRS research, with the intent of assisting the research community to lead innovative and impactful fNIRS studies in the field of posture and gait, whilst ensuring standardization of research.

Altered prefrontal cortex responses in older adults with subjective memory complaints and dementia during dual-task gait: An fNIRS study

People with cognitive impairments show deficits during physical performances such as gait, in particular during cognitively challenging conditions (i.e. dual-task gait [DTG]). However, it is unclear if people at risk of dementia, such as those with subjective memory complaints (SMC), also display gait and central deficits associated with DTG. In this study, we investigated the effects of single- and dual-task gait (STG and DTG), on left prefrontal cortex (PFC) activation in elderly people with subjective memory complaints (SMC) and Dementia. A total of 58 older adults (aged 65-94 years; 26 Healthy; 23 SMC; 9 Dementia) were recruited. Gait spatiotemporal characteristics (i.e. stride velocity and length) were assessed using an instrumented walkway during STG and DTG. Single-channel functional near-infrared spectroscopy over the left PFC was used to measure changes in oxyhaemoglobin (O₂ Hb) during gait. Stride velocity and length during STG (all p < .05) and DTG (all p < .000) were significantly impaired in people with Dementia compared to Healthy and SMC individuals. No differences were observed between Healthy and SMC. For STG, a greater increase in O₂ Hb (p < .05) was observed in those with Dementia compared to the Healthy and SMC, while no differences were observed between Healthy and SMC. A significant increase and decline in O₂ Hb was observed during DTG in the SMC and Dementia groups, respectively, compared to Healthy. Our findings indicate an altered pattern of cerebral haemodynamic response of the left PFC in DTG in people with SMC and Dementia, which may suggest that central changes precede functional impairments in people with SMC.

Cognitive Performance, Quality and Quantity of Movement Reflect Psychological Symptoms in Adolescents

The presentation of unhealthy psychological symptoms are rising sharply in adolescents. Detrimental lifestyle behaviours are proposed as both possible causes and consequences. This study set out to compare selected measures of quality and quantity of movement between adolescents with and without unhealthy psychological symptoms. Using a cross sectional design, 96 participants completed the study from a whole year group of 166, age (13.36 ± 0.48) male 50.6% from a secondary school in Oxfordshire, England as a part of a larger study (EPIC) between January and April 2018. Measures were taken of quality and quantity of movement: reaction/movement time, gait pattern & physical activity, alongside psychological symptoms. Differences in movement behaviour in relation to psychological symptom and emotional problem presentation were determined using ANOVA. In the event of a significant result for the main factor of each parameter, a Bonferroni -corrected post hoc test was conducted to show the difference between categories in each group. Results for both unhealthy psychological symptoms and emotional problems were grouped into four categories ('Close to average', 'slightly raised', 'high' and 'very high'). Early adolescents with very high unhealthy psychological symptoms had 16.79% slower reaction times (p = 0.003, η_p² = 0.170), 13.43% smaller walk ratio (p = 0.007, η_p² = 0.152), 7.13% faster cadence (p = 0.005, η_p² = 0.149), 6.95% less step time (p = 0.007, η_p² = 0.153) and 1.4% less vigorous physical activity (p = 0.04, η_p² = 0.102) than children with close to average psychological symptoms. Early adolescents with very high emotional problems had 12.25% slower reaction times (p = 0.05, η_p² = 0.081), 10.61% smaller walk ratio (p = 0.02, η_p² = 0.108), 6.03% faster cadence (p = 0.01, ηp² = 0.134), 6.07% shorter step time (p = 0.007, ηp² = 0.141) and 1.78% less vigorous physical activity (p = 0.009, ηp² = 0.136) than children with close to average emotional problems. Different movement quality and quantity of was present in adolescents with unhealthy psychological symptoms and emotional problems. We propose movement may be used to both monitor symptoms, and as a novel therapeutic behavioural approach. Further studies are required to confirm our findings.

Prefrontal cortical activation measured by fNIRS during walking: effects of age, disease and secondary task

Background

Cognitive processes are required during walking to appropriately respond to environmental and task demands. There are now many studies that have used functional Near-Infrared Spectroscopy (fNIRS) to record brain activation to investigate neural bases of cognitive contributions in gait. The aim of this systematic review was to summarize the published research regarding Prefrontal cortical (PFC) activation patterns during simple and complex walking tasks in young adults, older adults and clinical groups with balance disorders using fNIRS. Our secondary aim was to evaluate each included study based on methodological reporting criteria important for good data quality.

Methods

We conducted searches in June 2018 using four databases: Embase, PubMed, Scopus and PsycINFO. The strategy search used was: (((((near infrared spectroscopy) OR functional near infrared spectroscopy) OR nirs) OR fnirs) AND (((gait) OR walking) OR locomotion) AND (((((young) OR adult) OR older) OR elderly) NOT children)) AND (((Brain) OR cortex) OR cortical) for our search. The papers included met the specific review criteria: (i) used fNIRS to measure PFC activation patterns; (ii) included walking tasks (simple and complex) and; (iii) assessed young people, older people and/or clinical groups with balance disorders.

Results

Thirty five (describing 75 brain activation comparisons) of the 308 studies retrieved through our search met the inclusion criteria. Based on 6 methodological reporting considerations, 20 were of high quality, 10 were of medium quality and 5 were of low quality. Eleven/20 comparisons in young people, 23/37 comparisons in older people and 15/18 comparisons in clinical groups reported increased PFC activation with increased walking task complexity. The majority of comparisons that used verbal fluency, counting backwards or secondary motor tasks reported increases in PFC activation (83%, 64% and 58% of these studies, respectively). In contrast, no studies found secondary visual tasks increased PFC activation.

Conclusion

Increased PFC activation was most common in studies that involved walks comprising secondary verbal fluency and arithmetic tasks. Clinical groups generally showed increased PFC activation irrespective of type of secondary task performed during walking which suggests these groups require more attentional resources for safe walking. Systematic review registration number: PROSPERO 2017 - CRD42017059501.

Neural Substrates of Cognitive Motor Interference During Walking; Peripheral and Central Mechanisms

Current gait control models suggest that independent locomotion depends on central and peripheral mechanisms. However, less information is available on the integration of these mechanisms for adaptive walking. In this cross-sectional study, we investigated gait control mechanisms in people with Parkinson’s disease (PD) and healthy older (HO) adults: at self-selected walking speed (SSWS) and at fast walking speed (FWS). We measured effect of additional cognitive task (DT) and increased speed on prefrontal (PFC) and motor cortex (M1) activation, and Soleus H-reflex gain. Under DT-conditions we observed increased activation in PFC and M1. Whilst H-reflex gain decreased with additional cognitive load for both groups and speeds, H-reflex gain was lower in PD compared to HO while walking under ST condition at SSWS. Attentional load in PFC excites M1, which in turn increases inhibition on H-reflex activity during walking and reduces activity and sensitivity of peripheral reflex during the stance phase of gait. Importantly this effect on sensitivity was greater in HO. We have previously observed that the PFC copes with increased attentional load in young adults with no impact on peripheral reflexes and we suggest that gait instability in PD may in part be due to altered sensorimotor functioning reducing the sensitivity of peripheral reflexes.

Dual influences of early life stress induced by limited bedding on walking adaptability and Bdnf/TrkB and Drd1/Drd2 gene expression in different mouse brain regions

Introduction Evidence suggests early life stress impairs development, quality of life and increases vulnerability to disease. One important aspect of the stress experience is its impact on cognitive-motor performance, which includes the ability to adapt walking according to the environmental conditions. This study aimed to investigate how early-life stress affects walking adaptability of mice, while investigating BDNF/TrkB and Drd1/Drd2 expression in different brain regions. Methods Briefly, we exposed male C56BL/6 to the limited bedding protocol (LB) from post-natal day (PND) 2 to PND9 and then tested animals in the ladder walking task at PND60. RT-qPCR was used to investigate gene expression in the mPFC, hippocampus, motor cortex and cerebellum 2 h after the task Results LB induced a wide range of variability and therefore two distinct subgroups of animals within the LB group were established: a) superior performance (LB-SP); and b) inferior performance (LB-IP), compared to controls. Additionally, Drd1 gene expression was increased in the mPFC of LB-IP animals and in the cerebellum of LB-SP animals, while Drd2 expression was reduced in the hippocampus of the LB-IP group. BDNF exon IV gene expression in the mPFC and motor cortex was increased in both the LB-IP and LB-SP subgroups. TrkB gene expression in the hippocampus was reduced in the LB-IP group. A strong negative correlation was found between walking adaptability performance and BDNF exon IV gene expression in the motor cortex. Conversely, a positive correlation was found between walking adaptability performance and TrkB expression in the mPFC and a negative correlation in the hippocampus. Both Drd1 and Drd2 gene expression were negatively correlated with the ability to adapt walking. Conclusions Overall, our findings suggest exposure to early life stress leads to distinct walking adaptability phenotypes, which may be related to Drd1, Drd2, Bdnf exon IV and TrkB gene expression in brain regions that influence walking adaptability.

Analysis of Spatial and Temporal Step Parameters During Crutch-Assisted Gait as a Dual-Task: A Pilot Study

The main objective was to analyze the changes in the spatial and temporal step parameters during a dual-task: walking with a forearm crutch to partially unload the body weight of the subject. The secondary objective was to determine the influence of the use of the crutch with the dominant or nondominant hand in the essential gait parameters. Seven healthy subjects performed gait without crutches (GWC) and unilateral assisted gait (UAG) with the crutch carried out by dominant hand (dominant crutch (DC)) and nondominant hand (nondominant crutch (NDC)). Gait was recorded using a Vicon System; the GCH System 2.0 and the GCH Control Software 1.0 controlled the loads. The variables were step length, step period, velocity, step width, and step angle. The Wilcoxon signed-rank test compared GWC and UAG while also analyzing the parameters measured for both legs with DC and NDC in general and in each subject. Wilcoxon test only found significant differences in 1 of the 15 general comparisons between both legs. In the analysis by subject, step length, step period, and velocity showed significant differences between GWC and UAG. These parameters obtained less differences in DC. The effect of a forearm crutch on UAG caused a reduction in step length and velocity, and an increase in step period. However, it did not entail changes in step angle and step width. UAG was more effective when the DC carried the crutch. The unloading of 10% body weight produced an assisted gait which closely matched GWC.

Differentiation in Theta and Beta Electrocortical Activity between Visual and Physical Perturbations to Walking and Standing Balance

Human balance is a complex process in healthy adults, requiring precisely timed coordination among sensory information, cognitive processing, and motor control. It has been difficult to quantify brain dynamics during human balance control due to limitations in brain-imaging modalities. The goal of this study was to determine whether by using high-density electroencephalography (EEG) and independent component analysis, we can identify common cortical responses to visual and physical balance perturbations during walking and standing. We studied the responses of 30 healthy young adults to sensorimotor perturbations that challenged their balance. Subjects performed four 10 min trials of beam walking and tandem stance while either being mediolaterally pulled at the waist or viewing brief 20° field-of-view rotations in virtual reality. We recorded high-density EEG, motion capture, lower leg electromyography (EMG), and neck EMG. We hypothesized that both physical pull and visual rotation perturbations would elicit time-frequency fluctuations in theta (4-8 Hz) and beta (13-30 Hz) bands, with increased occipito-parietal activity during visual rotations compared with pull perturbations. Our results confirmed this hypothesis. For both perturbations, we found early theta synchronization and late alpha-beta (8-30 Hz) desynchronization following perturbation onset. This pattern was strongest in occipito-parietal areas during visual perturbations and strongest in sensorimotor areas during pull perturbations. These results suggest a similar time-frequency electrocortical pattern when humans respond to sensorimotor conflict, but with substantive differences in the brain areas involved for visual versus physical perturbations. Our findings may have important implications for assessing and training balance in individuals with and without motor disabilities.

Tapping the Full Potential? Jumping Performance of Volleyball Athletes in Game-Like Situations

Background: One key issue in elite interactive team sports is the simultaneous execution of motor actions (e.g., dribbling a ball) and perceptual-cognitive tasks (e.g., visually scanning the environment for action choices). In volleyball, one typical situation is to prepare and execute maximal block jumps after multiple-options decision-making and concurrent visual tracking of the ongoing game dynamics to find an optimal blocking location. Based on resource-related dual- and multi-tasking theories simultaneous execution of visual-cognitive and motor tasks may interfere with each other. Therefore, the aim of this study was to investigate whether volleyball-specific perceptual-cognitive demands (i.e., divided attention, decision making) affect blocking performance (i.e., jumping performance and length of the first step after the ready-block-position) compared to relatively isolated jumping performance.

Methods: Twenty-two elite volleyball players (1st – 3rd German league) performed block jumps in front of a net construction in a single-task condition (ST) and in two perceptual (-cognitive) dual-task conditions including a dual-task low (DT_L; presenting a picture of an opponent attack on a screen) and a dual-task high condition (DT_H; presenting videos of an offensive volleyball set play with a two-alternative choice).

Results: The results of repeated-measures ANOVAs showed a significant effect of conditions on jumping performance [F(2,42) = 33.64, p < 0.001, η_p² = 0.62] and on the length of the first step after the ready-block-position [F(2,42) = 7.90, p = 0.001, η_p² = 0.27). Post hoc comparisons showed that jumping performance in DT_H (p < 0.001) and DT_L (p < 0.001) was significantly lower than in ST. Also, length of the first step after the ready-block-position in DT_H (p = 0.005) and DT_L (p = 0.028) was significantly shorter than in ST.

Conclusion: Our findings suggest that blocking performance (i.e., jumping height, length of the first step) decreases in elite volleyball players when a perceptual (-cognitive) load is added. Based on the theory of Wickens (2002), this suggests a resource overlap between visual-processing demands for motor performance and for tracking the dynamics of the game. Interference with the consequence of dual-task related performance costs can therefore also be found in elite athletes in their specific motor expert domain.

Asymmetric interference between cognitive task components and concurrent sensorimotor coordination

Everyday cognitive tasks are frequently performed under dual-task conditions alongside continuous sensorimotor coordinations (CSCs) such as driving, walking, or balancing. Observed interference in these dual-task settings is commonly attributed to demands on executive function or attentional resources, but the time course and reciprocity of interference are not well understood at the level of information-processing components. Here we used electrophysiology to study the detailed chronometry of dual-task interference between a visual oddball task and a continuous visuomanual tracking task. The oddball task's electrophysiological components were linked to underlying cognitive processes, and the tracking task served as a proxy for the continuous cycle of state monitoring and adjustment inherent to CSCs. Dual-tasking interfered with the oddball task's accuracy and attentional processes (attenuated P2 and P3b magnitude and parietal alpha-band event-related desynchronization), but errors in tracking due to dual-tasking accrued at a later timescale and only in trials in which the target stimulus appeared and its tally had to be incremented. Interference between cognitive tasks and CSCs can be asymmetric in terms of timing as well as affected information-processing components. NEW & NOTEWORTHY Interference between cognitive tasks and continuous sensorimotor coordination (CSC) has been widely reported, but this is the first demonstration that the cognitive operation that is impaired by concurrent CSC may not be the one that impairs the CSC. Also demonstrated is that interference between such tasks can be temporally asymmetric. The asynchronicity of this interference has significant implications for understanding and mitigating loss of mobility in old age, and for rehabilitation for neurological impairments.

Treadmill walking reduces pre-frontal activation in patients with Parkinson's disease

BACKGROUND

Among patients with Parkinson's disease (PD), gait is typically disturbed and less automatic. These gait changes are associated with impaired rhythmicity and increased prefrontal activation, presumably in an attempt to compensate for reduced automaticity.

RESEARCH QUESTION

We investigated whether during treadmill walking, when the pace is determined and fixed, prefrontal activation in patients with PD is lower, as compared to over-ground walking.

METHODS

Twenty patients with PD (age: 69.8 ± 6.5 yrs.; MoCA: 26.9 ± 2.4; disease duration: 7.9 ± 4.2 yrs) walked at a self-selected walking speed over-ground and on a treadmill. A wireless functional near infrared spectroscopy (fNIRS) system measured prefrontal lobe activation, i.e., oxygenated hemoglobin (Hb02) in the pre-frontal area. Gait was evaluated using 3D-accelerometers attached to the lower back and ankles (Opal™, APDM). Dynamic gait stability was assessed using the maximum Lyapunov exponent to investigate automaticity of the walking pattern.

RESULTS

Hb02 was lower during treadmill walking than during over-ground walking (p = 0.001). Gait stability was greater on the treadmill, compared to over-ground walking, in both the anteroposterior and medio-lateral axes (p < 0.001).

SIGNIFICANCE

These findings support the notion that when gait is externally paced, prefrontal lobe activation is reduced in patients with PD, perhaps reflecting a reduced need for compensatory cognitive mechanisms.

Prefrontal over-activation during walking in people with mobility deficits: Interpretation and functional implications

BACKGROUND

Control of walking by the central nervous system includes contributions from executive control mechanisms, such as attention and motor planning resources. Executive control of walking can be estimated objectively by recording prefrontal cortical activity using functional near infrared spectroscopy (fNIRS).

OBJECTIVE

The primary objective of this study was to investigate group differences in prefrontal/executive control of walking among young adults, older adults, and adults post-stroke. Also assessed was the extent to which walking-related prefrontal activity fits existing cognitive frameworks of prefrontal over-activation.

METHODS

Participants included 24 adults post-stroke with moderate to severe walking deficits, 15 older adults with mild gait deficits, and 9 young healthy adults. Executive control of walking was quantified as oxygenated hemoglobin concentration in the prefrontal cortex measured by fNIRS. Three walking tasks were assessed: typical walking, walking over obstacles, and walking while performing a verbal fluency task. Walking performance was assessed by walking speed.

RESULTS

There was a significant effect of group for prefrontal activity (p < 0.001) during typical and obstacles walking tasks, with young adults exhibiting the lowest level of prefrontal activity, followed by older adults, and then adults post-stroke. In young adults the prefrontal activity during typical walking was much lower than for the verbal fluency dual-task, suggesting substantial remaining prefrontal resources during typical walking. However, in older and post-stroke adults these remaining resources were significantly less (p < 0.01). Cumulatively, these results are consistent with prefrontal over-activation in the older and stroke groups, which was accompanied by a steeper drop in walking speed as task complexity increased to include obstacles (p < 0.05).

CONCLUSIONS

There is a heightened use of prefrontal/executive control resources in older adults and post-stroke adults during walking. The level of prefrontal resource utilization, particularly during complex walking tasks like obstacle crossing, may approach the ceiling of available resources for people who have walking deficits. Prior cognitive research has revealed that prefrontal over-activation combined with limited prefrontal resources can lead to poor cognitive performance. The present study suggests a similar situation influences walking performance. Future research should further investigate the extent to which prefrontal over-activation during walking is linked to adverse mobility outcomes.

Effects of trying 'not to move' instruction on cortical load and concurrent cognitive performance

Motor and cognitive tasks often interfere when performed concurrently. The amount of interference typically scales with difficulty of the tasks involved. Thus, supposedly 'easy' motor tasks with restricted movement amplitude, like sitting on a chair, should show little or no interference with cognitive tasks at all. We measured the processing load induced by different postural tasks and their effect on cognitive performance under cognitive-motor dual-task conditions. Sixteen subjects performed postural motor tasks in three different positions: 'Lying in a sun lounger', 'Sitting on a bike saddle', and 'Upright on feet'. In each position, three different movement instructions were given; 'Stay stock-still', 'Relax', 'Move easily'. Each combination of position and instruction was performed as single task but also in a dual-task condition with a concurrent calculation task. Brain activity in the right prefrontal cortex was monitored using functional near-infrared spectroscopy. The instruction to 'Stay stock-still' produced higher cortical loads in single-task conditions for all positions compared to all other instructions. The calculation task induced additional brain activity in the same prefrontal area as the motor task. Calculation performance tended to be reduced in the 'Lying'-'Stay stock-still' condition. We discuss the relevance of these findings for learning scenarios in school.

Functional near-infrared spectroscopy in movement science: a systematic review on cortical activity in postural and walking tasks

Safe locomotion is a crucial aspect of human daily living that requires well-functioning motor control processes. The human neuromotor control of daily activities such as walking relies on the complex interaction of subcortical and cortical areas. Technical developments in neuroimaging systems allow the quantification of cortical activation during the execution of motor tasks. Functional near-infrared spectroscopy (fNIRS) seems to be a promising tool to monitor motor control processes in cortical areas in freely moving subjects. However, so far, there is no established standardized protocol regarding the application and data processing of fNIRS signals that limits the comparability among studies. Hence, this systematic review aimed to summarize the current knowledge about application and data processing in fNIRS studies dealing with walking or postural tasks. Fifty-six articles of an initial yield of 1420 publications were reviewed and information about methodology, data processing, and findings were extracted. Based on our results, we outline the recommendations with respect to the design and data processing of fNIRS studies. Future perspectives of measuring fNIRS signals in movement science are discussed.

Walking on uneven terrain in healthy adults and the implications for people after stroke

BACKGROUND

One third of individuals after stroke report an inability to walk in the community. Community mobility requires walking adaptability - the ability to adjust one's stepping pattern to meet environmental demands and task goals. Walking on uneven terrain (e.g. grass, gravel) has unique requirements and is a critical component of walking adaptability that has not been investigated in the post-stroke population.

OBJECTIVE

To summarize current knowledge of biomechanical and neuromuscular modifications during uneven terrain negotiation in healthy individuals and discuss implications of post-stroke impairments.

METHODS

Review of eleven studies, identified through a search of relevant literature on PubMed and CINAHL.

RESULTS

On uneven terrain, healthy adults demonstrate numerous gait modifications including a lowered center of mass, increased muscle co-contraction during stance and exaggerated or increased toe clearance during swing. After stroke, changes in muscle activity and limb coordination will likely result in difficulty or inability performing these modifications that healthy adults use to maintain stability and safety when walking on uneven terrain.

CONCLUSIONS

Studies of biomechanical and neuromuscular control of walking on uneven terrain are needed to quantify mobility limitations in adults post-stroke. Such investigations will contribute to the understanding of mobility impairments after stroke and the design of critically important intervention strategies.

Increasing cognitive load attenuates right arm swing in healthy human walking

Human arm swing looks and feels highly automated, yet it is increasingly apparent that higher centres, including the cortex, are involved in many aspects of locomotor control. The addition of a cognitive task increases arm swing asymmetry during walking, but the characteristics and mechanism of this asymmetry are unclear. We hypothesized that this effect is lateralized and a Stroop word-colour naming task-primarily involving left hemisphere structures-would reduce right arm swing only. We recorded gait in 83 healthy subjects aged 18-80 walking normally on a treadmill and while performing a congruent and incongruent Stroop task. The primary measure of arm swing asymmetry-an index based on both three-dimensional wrist trajectories in which positive values indicate proportionally smaller movements on the right-increased significantly under dual-task conditions in those aged 40-59 and further still in the over-60s, driven by reduced right arm flexion. Right arm swing attenuation appears to be the norm in humans performing a locomotor-cognitive dual-task, confirming a prominent role of the brain in locomotor behaviour. Women under 60 are surprisingly resistant to this effect, revealing unexpected gender differences atop the hierarchical chain of locomotor control.

Measuring prefrontal cortical activity during dual task walking in patients with Parkinson's disease: feasibility of using a new portable fNIRS device

BACKGROUND

Many patients with Parkinson's disease (PD) have difficulties in performing a second task during walking (i.e., dual task walking). Functional near-infrared spectroscopy (fNIRS) is a promising approach to study the presumed contribution of dysfunction within the prefrontal cortex (PFC) to such difficulties. In this pilot study, we examined the feasibility of using a new portable and wireless fNIRS device to measure PFC activity during different dual task walking protocols in PD. Specifically, we tested whether PD patients were able to perform the protocol and whether we were able to measure the typical fNIRS signal of neuronal activity.

METHODS

We included 14 PD patients (age 71.2 ± 5.4 years, Hoehn and Yahr stage II/III). The protocol consisted of five repetitions of three conditions: walking while (i) counting forwards, (ii) serially subtracting, and (iii) reciting digit spans. Ability to complete this protocol, perceived exertion, burden of the fNIRS devices, and concentrations of oxygenated (O2Hb) and deoxygenated (HHb) hemoglobin from the left and right PFC were measured.

RESULTS

Two participants were unable to complete the protocol due to fatigue and mobility safety concerns. The remaining 12 participants experienced no burden from the two fNIRS devices and completed the protocol with ease. Bilateral PFC O2Hb concentrations increased during walking while serially subtracting (left PFC 0.46 μmol/L, 95 % confidence interval (CI) 0.12-0.81, right PFC 0.49 μmol/L, 95 % CI 0.14-0.84) and reciting digit spans (left PFC 0.36 μmol/L, 95 % CI 0.03-0.70, right PFC 0.44 μmol/L, 95 % CI 0.09-0.78) when compared to rest. HHb concentrations did not differ between the walking tasks and rest.

CONCLUSIONS

These findings suggest that a new wireless fNIRS device is a feasible measure of PFC activity in PD during dual task walking. Future studies should reduce the level of noise and inter-individual variability to enable measuring differences in PFC activity between different dual walking conditions and across health states.

Prefrontal Cortex Activation While Walking Under Dual-Task Conditions in Stroke: A Multimodal Imaging Study

Background Walking while performing another task (eg, talking) is challenging for many stroke survivors, yet its neural basis are not fully understood. Objective To investigate prefrontal cortex activation and its relationship to gait measures while walking under single-task (ST) and dual-task (DT) conditions (ie, walking while simultaneously performing a cognitive task) in stroke survivors. Methods We acquired near-infrared spectroscopy (NIRS) data from the prefrontal cortex during treadmill walking in ST and DT conditions in chronic stroke survivors and healthy controls. We also acquired functional magnetic resonance imaging (fMRI) and NIRS during simulated walking under these conditions. Results NIRS revealed increased oxygenated hemoglobin concentration in DT-walking compared with ST-walking for both groups. For simulated walking, NIRS showed a significant effect of group and group × task, being greater on both occasions, in stroke survivors. A greater increase in brain activation observed from ST to DT walking/ simulated walking was related to a greater change in motor performance in stroke survivors. fMRI revealed increased activity during DT relative to ST conditions in stroke patients in areas including the inferior temporal gyri, superior frontal gyri and cingulate gyri bilaterally, and the right precentral gyrus. The DT-related increase in fMRI activity correlated with DT-related change in behavior in stroke participants in the bilateral inferior temporal gyrus, left cingulate gyrus, and left frontal pole. Conclusion Our results provide novel evidence that enhanced brain activity changes relate to dual task motor decrements.

Exergame and Balance Training Modulate Prefrontal Brain Activity during Walking and Enhance Executive Function in Older Adults

Different types of exercise training have the potential to induce structural and functional brain plasticity in the elderly. Thereby, functional brain adaptations were observed during cognitive tasks in functional magnetic resonance imaging studies that correlated with improved cognitive performance. This study aimed to investigate if exercise training induces functional brain plasticity during challenging treadmill walking and elicits associated changes in cognitive executive functions. Forty-two elderly participants were recruited and randomly assigned to either interactive cognitive-motor video game dancing (DANCE) or balance and stretching training (BALANCE). The 8-week intervention included three sessions of 30 min per week and was completed by 33 participants (mean age 74.9 ± 6.9 years). Prefrontal cortex (PFC) activity during preferred and fast walking speed on a treadmill was assessed applying functional near infrared spectroscopy pre- and post-intervention. Additionally, executive functions comprising shifting, inhibition, and working memory were assessed. The results showed that both interventions significantly reduced left and right hemispheric PFC oxygenation during the acceleration of walking (p < 0.05 or trend, r = 0.25-0.36), while DANCE showed a larger reduction at the end of the 30-s walking task compared to BALANCE in the left PFC [F (1, 31) = 3.54, p = 0.035, r = 0.32]. These exercise training induced modulations in PFC oxygenation correlated with improved executive functions (p < 0.05 or trend, r = 0.31-0.50). The observed reductions in PFC activity may release cognitive resources to focus attention on other processes while walking, which could be relevant to improve mobility and falls prevention in the elderly. This study provides a deeper understanding of the associations between exercise training, brain function during walking, and cognition in older adults.

Maintaining Gait Performance by Cortical Activation during Dual-Task Interference: A Functional Near-Infrared Spectroscopy Study

In daily life, mobility requires walking while performing a cognitive or upper-extremity motor task. Although previous studies have evaluated the effects of dual tasks on gait performance, few studies have evaluated cortical activation and its association with gait disturbance during dual tasks. In this study, we simultaneously assessed gait performance and cerebral oxygenation in the bilateral prefrontal cortices (PFC), premotor cortices (PMC), and supplemental motor areas (SMA), using functional near-infrared spectroscopy, in 17 young adults performing dual tasks. Each participant was evaluated while performing normal-pace walking (NW), walking while performing a cognitive task (WCT), and walking while performing a motor task (WMT). Our results indicated that the left PFC exhibited the strongest and most sustained activation during WCT, and that NW and WMT were associated with minor increases in oxygenation levels during their initial phases. We observed increased activation in channels in the SMA and PMC during WCT and WMT. Gait data indicated that WCT and WMT both caused reductions in walking speed, but these reductions resulted from differing alterations in gait properties. WCT was associated with significant changes in cadence, stride time, and stride length, whereas WMT was associated with reductions in stride length only. During dual-task activities, increased activation of the PMC and SMA correlated with declines in gait performance, indicating a control mechanism for maintaining gait performance during dual tasks. Thus, the regulatory effects of cortical activation on gait behavior enable a second task to be performed while walking.

Automaticity of walking: functional significance, mechanisms, measurement and rehabilitation strategies

Automaticity is a hallmark feature of walking in adults who are healthy and well-functioning. In the context of walking, “automaticity” refers to the ability of the nervous system to successfully control typical steady state walking with minimal use of attention-demanding executive control resources. Converging lines of evidence indicate that walking deficits and disorders are characterized in part by a shift in the locomotor control strategy from healthy automaticity to compensatory executive control. This is potentially detrimental to walking performance, as an executive control strategy is not optimized for locomotor control. Furthermore, it places excessive demands on a limited pool of executive reserves. The result is compromised ability to perform basic and complex walking tasks and heightened risk for adverse mobility outcomes including falls. Strategies for rehabilitation of automaticity are not well defined, which is due to both a lack of systematic research into the causes of impaired automaticity and to a lack of robust neurophysiological assessments by which to gauge automaticity. These gaps in knowledge are concerning given the serious functional implications of compromised automaticity. Therefore, the objective of this article is to advance the science of automaticity of walking by consolidating evidence and identifying gaps in knowledge regarding: (a) functional significance of automaticity; (b) neurophysiology of automaticity; (c) measurement of automaticity; (d) mechanistic factors that compromise automaticity; and (e) strategies for rehabilitation of automaticity.

Dual-task and electrophysiological markers of executive cognitive processing in older adult gait and fall-risk

The role of cognition is becoming increasingly central to our understanding of the complexity of walking gait. In particular, higher-level executive functions are suggested to play a key role in gait and fall-risk, but the specific underlying neurocognitive processes remain unclear. Here, we report two experiments which investigated the cognitive and neural processes underlying older adult gait and falls. Experiment 1 employed a dual-task (DT) paradigm in young and older adults, to assess the relative effects of higher-level executive function tasks (n-Back, Serial Subtraction and visuo-spatial Clock task) in comparison to non-executive distracter tasks (motor response task and alphabet recitation) on gait. All DTs elicited changes in gait for both young and older adults, relative to baseline walking. Significantly greater DT costs were observed for the executive tasks in the older adult group. Experiment 2 compared normal walking gait, seated cognitive performances and concurrent event-related brain potentials (ERPs) in healthy young and older adults, to older adult fallers. No significant differences in cognitive performances were found between fallers and non-fallers. However, an initial late-positivity, considered a potential early P3a, was evident on the Stroop task for older non-fallers, which was notably absent in older fallers. We argue that executive control functions play a prominent role in walking and gait, but the use of neurocognitive processes as a predictor of fall-risk needs further investigation.