Towards an understanding of gait control: brain activation during the anticipation, preparation and execution of foot movements

Central imaging based on near-infrared functional imaging technology can be useful to plan management in patients with chronic lateral ankle instability

BACKGROUND

Near infrared brain functional imaging (FNIRS) has been used for the evaluation of brain functional areas, the imaging differences of central activation of cognitive-motor dual tasks between patients with chronic lateral ankle instability (CLAI) and healthy population remain unclear. This study aimed to evaluated the role of central imaging based on FNIRS technology on the plan management in patients with CLAI, to provide insights to the clinical treatment of CLAI.

METHODS

CLAI patients treated in our hospital from January 1, 2021 to June 31, 2022 were selected. Both CLAI patients and health controls were intervened with simple task and cognitive-motor dual task under sitting and walking conditions, and the changes of oxygenated hemoglobin concentration in bilateral prefrontal cortex (PFC), premotor cortex (PMC) and auxiliary motor area (SMA) were collected and compared.

RESULTS

A total of 23 participants were enrolled. There were significant differences in the fNIRS ΔHbO2 of barefoot subtractive walking PFC-R and barefoot subtractive walking SMA-R between experimental and control group (all P < 0.05). There was no significant difference in ΔHbO2 between the experimental group and the control group in other states (P > 0.05). There was no significant difference in ΔHbO2 between the experimental group and the control group in each state of the brain PMC region.

CONCLUSION

Adaptive alterations may occur within the relevant brain functional regions of individuals with CLAI. The differential activation observed between the PFC and the SMA could represent a compensatory mechanism emerging from proprioceptive afferent disruptions following an initial ankle sprain.

Differences in Cortical Activation During Dorsiflexion and Plantarflexion in Chronic Ankle Instability: A Task-fMRI Study

BACKGROUND

Chronic ankle instability is a common sports injury that often presents with increased plantarflexion and restricted dorsiflexion. The cumulative effect of peripheral injuries may induce neuroplasticity in the central nervous system. However, the relationship between dorsiflexion or plantarflexion and the central nervous system in patients with chronic ankle instability remains unknown.

QUESTIONS/PURPOSES

(1) Is there a difference in region and voxel (volume pixel) of cortical activation during plantarflexion and dorsiflexion between patients with chronic ankle instability and a control group with normal ankle function? (2) Is there a correlation between activation of sensorimotor-related brain regions and three clinical measurement scales of ankle function and disease severity in patients with chronic ankle instability?

METHODS

Between December 2020 and May 2022, we treated 400 patients who had chronic ankle instability. Ten percent (40 patients; mean ± standard deviation age 29 ± 7 years; 17 male patients) were randomly selected to participate in this study. We recruited 42 volunteers with normal ankle function (mean age 28 ± 5 years; 21 male participants) matched by age and education level. A total of 2.5% (1 of 40) of patients with bilateral chronic ankle instability and 30% (12 of 40) with left-sided chronic ankle injury did not meet our inclusion criteria and were excluded from the study. The control group underwent MRI with good image quality. Finally, 27 patients with chronic ankle instability (mean age 26 ± 5 years; 10 male patients) and 42 participants with normal ankle function were enrolled. Ankle function and disease severity were assessed using three clinical scales: the Cumberland Ankle Instability Tool, Karlsson-Peterson Ankle Function Score, and the American Orthopedic Foot and Ankle Society Score. A uniplanar and nonweightbearing ankle dorsiflexion-plantarflexion paradigm (a recognized model or pattern) was performed using a short-block design during the functional MRI scan. This experimental design included a series of on-off periods consisting of movement and a rest period. From 15° of plantarflexion to 15° of dorsiflexion, the manipulator allowed 30° of ankle rotation. The cerebral excitability patterns between patients with chronic ankle instability and controls were analyzed using t-tests. We retained voxels with p values less than 0.05 in a voxel-level family-wise error correction. Clusters with voxel numbers greater than 10 were retained. The Cohen d coefficient was used to calculate between-group effect sizes. Spearman analysis was performed to explore the correlation between activation regions and the three clinical assessment scales.

RESULTS

In the patient group, cortical activation was greater during plantarflexion than during dorsiflexion, which was different from that in the control group. The between-group comparison showed that patients with chronic ankle instability had reduced activation in the ipsilateral precuneus (cluster size = 35 voxels [95% CI -0.23 to 0.07]; p < 0.001) during dorsiflexion, whereas during plantarflexion, chronic ankle instability caused increased activation in the ipsilateral superior temporal gyrus (cluster size = 90 voxels [95% CI -0.73 to -0.13]; p < 0.001), precuneus (cluster size = 18 voxels [95% CI -0.56 to -0.19]; p < 0.001), supplementary motor area (cluster size = 57 voxels [95% CI -0.31 to 0.00]; p < 0.001), superior frontal gyrus (cluster size = 43 voxels [95% CI -0.82 to -0.29]; p < 0.001), medial part of the superior frontal gyrus (cluster size = 39 voxels [95% CI 0.41 to 0.78]; p < 0.001), and contralateral postcentral gyrus (cluster size = 100 voxels [95% CI -0.32 to 0.02]; p < 0.001). Patients with chronic ankle instability showed a large effect size compared with controls (Cohen d > 0.8). During plantarflexion, the number of activated voxels in the supplementary motor area had a modest, positive correlation with the Karlsson-Peterson Ankle Function Score (r = 0.52; p = 0.01), and the number of activated voxels in the primary motor cortex (M1) and primary sensory cortex (S1) had a weak, positive correlation with the American Orthopedic Foot and Ankle Society Score in patients with chronic ankle instability (M1: r = 0.45; p = 0.02, S1: r = 0.49; p = 0.01).

CONCLUSION

Compared with volunteers with normal ankle function, patients with chronic ankle instability had increased cortical activation during plantarflexion and decreased cortical activation during dorsiflexion. We analyzed the central neural mechanisms of chronic ankle instability in patients with sports injuries and provided a theoretical basis for the development of new central and peripheral interventions in the future.

CLINICAL RELEVANCE

Because there was a positive correlation between the neural activity in sensorimotor-related regions during plantarflexion and clinical severity, clinicians might one day be able to help patients who have chronic ankle instability with neuromuscular rehabilitation by applying electrical stimulation to specific targets (such as S1M1 and the supplementary motor area) or by increasing activation of sensorimotor neurons through ankle movement.

Use of functional magnetic resonance imaging to identify cortical loci for lower limb movements and their efficacy for individuals after stroke

BACKGROUND

Identification of cortical loci for lower limb movements for stroke rehabilitation is crucial for better rehabilitation outcomes via noninvasive brain stimulation by targeting the fine-grained cortical loci of the movements. However, identification of the cortical loci for lower limb movements using functional MRI (fMRI) is challenging due to head motion and difficulty in isolating different types of movement. Therefore, we developed a custom-made MR-compatible footplate and leg cushion to identify the cortical loci for lower limb movements and conducted multivariate analysis on the fMRI data. We evaluated the validity of the identified loci using both fMRI and behavioral data, obtained from healthy participants as well as individuals after stroke.

METHODS

We recruited 33 healthy participants who performed four different lower limb movements (ankle dorsiflexion, ankle rotation, knee extension, and toe flexion) using our custom-built equipment while fMRI data were acquired. A subgroup of these participants (Dataset 1; n = 21) was used to identify the cortical loci associated with each lower limb movement in the paracentral lobule (PCL) using multivoxel pattern analysis and representational similarity analysis. The identified cortical loci were then evaluated using the remaining healthy participants (Dataset 2; n = 11), for whom the laterality index (LI) was calculated for each lower limb movement using the cortical loci identified for the left and right lower limbs. In addition, we acquired a dataset from 15 individuals with chronic stroke for regression analysis using the LI and the Fugl-Meyer Assessment (FMA) scale.

RESULTS

The cortical loci associated with the lower limb movements were hierarchically organized in the medial wall of the PCL following the cortical homunculus. The LI was clearer using the identified cortical loci than using the PCL. The healthy participants (mean ± standard deviation: 0.12 ± 0.30; range: - 0.63 to 0.91) exhibited a higher contralateral LI than the individuals after stroke (0.07 ± 0.47; - 0.83 to 0.97). The corresponding LI scores for individuals after stroke showed a significant positive correlation with the FMA scale for paretic side movement in ankle dorsiflexion (R2 = 0.33, p = 0.025) and toe flexion (R2 = 0.37, p = 0.016).

CONCLUSIONS

The cortical loci associated with lower limb movements in the PCL identified in healthy participants were validated using independent groups of healthy participants and individuals after stroke. Our findings suggest that these cortical loci may be beneficial for the neurorehabilitation of lower limb movement in individuals after stroke, such as in developing effective rehabilitation interventions guided by the LI scores obtained for neuronal activations calculated from the identified cortical loci across the paretic and non-paretic sides of the brain.

Discrepant changes in structure-function coupling in dancers and musicians

Dance and music are well known to improve sensorimotor skills and cognitive functions. To reveal the underlying mechanism, previous studies focus on the brain plastic structural and functional effects of dance and music training. However, the discrepancy training effects on brain structure-function relationship are still blurred. Thus, proficient dancers, musicians, and controls were recruited in this study. The graph signal processing framework was employed to quantify the region-level and network-level relationship between brain function and structure. The results showed the increased coupling strength of the right ventromedial putamen in the dance and music groups. Distinctly, enhanced coupling strength of the ventral attention network, increased coupling strength of the right inferior frontal gyrus opercular area, and increased function connectivity of coupling function signal between the right and left middle frontal gyrus were only found in the dance group. Besides, the dance group indicated enhanced coupling function connectivity between the left inferior parietal lobule caudal area and the left superior parietal lobule intraparietal area compared with the music groups. The results might illustrate dance and music training's discrepant effect on the structure-function relationship of the subcortical and cortical attention networks. Furthermore, dance training seemed to have a greater impact on these networks.

Re-learning mental representation of walking after a brain lesion. Effects of a cognitive-motor training with a robotic orthosis

Introduction

Stroke-related deficits often include motor impairments and gait dysfunction, leading to a limitation of social activities and consequently affecting the quality of life of stroke survivors. Neurorehabilitation takes advantage of the contribution of different techniques in order to achieve more benefits for patients. Robotic devices help to improve the outcomes of physical rehabilitation. Moreover, motor imagery seems to play a role in neurological rehabilitation since it leads to the activation of the same brain areas as actual movements. This study investigates the use of a combined physical and cognitive protocol for gait rehabilitation in stroke patients.

Methods

Specifically, we tested the efficacy of a 5-week training program using a robotic orthosis (P.I.G.R.O.) in conjunction with motor imagery training. Twelve chronic stroke patients participated in the study. We evaluated balance and gait performance before and after the training. Six of them underwent fMRI examination before and after the training to assess the effects of the protocol on brain plasticity mechanisms in motor and imagery tasks.

Results

Our results show that the rehabilitation protocol can effectively improve gait performance and balance and reduce the risk of falls in stroke patients. Furthermore, the fMRI results suggest that rehabilitation is associated with cerebral plastic changes in motor networks.

Discussion

The present findings, if confirmed by future research, have the potential to advance the development of new, more effective rehabilitation approaches for stroke patients, improving their quality of life and reducing the burden of stroke-related disability.

Assessing the Dose-Dependent Effects of tDCS on Neurometabolites using Magnetic Resonance Spectroscopy

Concurrent transcranial direct current stimulation (tDCS) and proton Magnetic Resonance Spectroscopy ( ¹ H MRS) experiments have shown up- or downregulation of neurotransmitter concentration. However, effects have been modest applying mostly lower current doses and not all studies found significant effects. Dose of stimulation might be an important variable in eliciting a consistent response. To investigate dose effects of tDCS on neurometabolites, we placed an electrode over the left supraorbital region (with a return electrode over the right mastoid bone) and utilized an MRS voxel (3x3x3cm) that was centered over the anterior cingulate/inferior mesial prefrontal region which is in the path of the current distribution. We conducted 5 epochs of acquisition, each one with a 9:18min acquisition time, and applied tDCS in the third epoch. We observed significant dose and polarity dependent modulation of GABA and to a lesser degree of Glutamine/Glutamate (GLX) with the highest and reliable changes seen with the highest current dose, 5mA (current density 0.39 mA/cm ² ), during and after the stimulation epoch compared with pre-stimulation baselines. The strong effect on GABA concentration (achieving a mean change of 63% from baseline, more than twice as much as reported with lower doses of stimulation) establishes tDCS-dose as an important parameter in eliciting a regional brain engagement and response. Furthermore, our experimental design in examining tDCS parameters and effects using shorter epochs of acquisitions might constitute a framework to explore the tDCS parameter space further and establish measures of regional engagement by non-invasive brain-stimulation.

Verification of propagation hypothesis in patients with sporadic hand onset amyotrophic lateral sclerosis

OBJECTIVE

If lesions in sporadic amyotrophic lateral sclerosis (ALS) originate from a single focal onset site and spread contiguously by prion-like cell-to-cell propagation at a constant speed, the lesion spread time should be proportional to the anatomical distance. We verify this model in the patients.

METHODS

In 29 sporadic ALS patients with hand onset followed by spread to shoulder and leg, we retrospectively evaluated the inter/intra-regional spread time ratio: time interval of symptoms from hand-to-leg divided by that from hand-to-shoulder. We also obtained the corresponding inter-/intra-regional distance ratios of spinal cord from magnetic resonance imaging of 12 patients, and those of primary motor cortex from coordinates using neuroimaging software.

RESULTS

Inter-/intra-regional spread time ratios ranged from 0.29 to 6.00 (median 1.20). Distance ratios ranged from 1.85 to 2.86 in primary motor cortex and from 5.79 to 8.67 in spinal cord. Taken together with clinical manifestations, of 27 patients with the requisite information available, lesion spreading was consistent with the model in primary motor cortex in 4 (14.8%) patients, and in spinal cord in only 1 (3.7%) patient. However, in more patients (12 of 29 patients: 41.4%), the inter-regional spread times in a long anatomical distance of hand-to-leg were shorter than or equal to the intra-regional spread times in a short anatomical distance of hand-to-shoulder.

CONCLUSION

Contiguous cell-to-cell propagation at a constant speed might not play a major role at least in distant lesion spreading of ALS. Several mechanisms can be responsible for progression in ALS.

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.

Altered frontoparietal activity in acoustic startle priming tasks during reticulospinal tract facilitation: An fNIRS study

Background

Because it is one of the important pathways for promoting motor recovery after cortical injury, the function of the reticulospinal tract (RST) has received increasing attention in recent years. However, the central regulatory mechanism of RST facilitation and reduction of apparent response time is not well understood.

Objectives

To explore the potential role of RST facilitation in the acoustic startle priming (ASP) paradigm and observe the cortical changes induced by ASP reaching tasks.

Methods

Twenty healthy participants were included in this study. The reaching tasks were performed with their left and right hands. Participants were instructed to get ready after the warning cue and complete the reach as soon as they heard the Go cue. Half of the testing trials were set as control trials with an 80-dB Go cue. The other half of the trials had the Go cue replaced with 114-dB white noise to evoke the StartleReact effect, inducing reticulospinal tract facilitation. The response of the bilateral sternocleidomastoid muscle (SCM) and the anterior deltoid was recorded via surface electromyography. Startle trials were labeled as exhibiting a positive or negative StartleReact effect, according to whether the SCM was activated early (30-130 ms after the Go cue) or late, respectively. Functional near-infrared spectroscopy was used to synchronously record the oxyhemoglobin and deoxyhemoglobin fluctuations in bilateral motor-related cortical regions. The β values representing cortical responses were estimated via the statistical parametric mapping technique and included in the final analyses.

Results

Separate analyses of data from movements of the left or right side revealed significant activation of the right dorsolateral prefrontal cortex during RST facilitation. Moreover, left frontopolar cortex activation was greater in positive startle trials than in control or negative startle trials during left-side movements. Furthermore, decreased activity of the ipsilateral primary motor cortex in positive startle trials during ASP reaching tasks was observed.

Conclusion

The right dorsolateral prefrontal cortex and the frontoparietal network to which it belongs may be the regulatory center for the StartleReact effect and RST facilitation. In addition, the ascending reticular activating system may be involved. The decreased activity of the ipsilateral primary motor cortex suggests enhanced inhibition of the non-moving side during the ASP reaching task. These findings provide further insight into the SE and into RST facilitation.

Cerebral control of swallowing: An update on neurobehavioral evidence

This review aims to update the current knowledge on the cerebral control of swallowing. We review data from both animal and human studies spanning across the fields of neuroanatomy, neurophysiology and neuroimaging to evaluate advancements in our understanding in the brain's role in swallowing. Studies have collectively shown that swallowing is mediated by multiple distinct cortical and subcortical regions and that lesions to these regions can result in dysphagia. These regions are functionally connected in separate groups within and between the two hemispheres. While hemispheric dominance for swallowing has been reported in most human studies, the laterality is inconsistent across individuals. Moreover, there is a shift in activation location and laterality between swallowing preparation and execution, although such activation changes are less well-defined than that for limb motor control. Finally, we discussed recent neurostimulation treatments that may be beneficial for dysphagia after brain injury through promoting the reorganization of the swallowing neural network.

Closing the loop: Novel quantitative fMRI approach for manipulation of the sensorimotor loop in tremor

Tremor is thought to be an effect of oscillatory activity within the sensorimotor network. To date, the underlying pathological brain networks are not fully understood. Disentangling tremor activity from voluntary motor output and sensorimotor feedback systems is challenging. To better understand the intrinsic sensorimotor fingerprint underlying tremor, we aimed to disentangle the sensorimotor system into driving (motor) and feedback/compensatory (sensory) neuronal involvement, and aimed to pinpoint tremor activity in essential tremor (ET) and tremor-dominant Parkinson's disease (PD) with a novel closed-loop approach. Eighteen ET patients, 14 tremor-dominant PD patients, and 18 healthy controls were included. An MR-compatible wrist manipulator was employed during functional MRI (fMRI) while muscle activity during (in)voluntary movements was concurrently recorded using electromyography (EMG). Tremor was quantified based on EMG and correlated to brain activity. Participants performed three tasks: an active wrist motor task, a passive wrist movement task, and rest (no wrist movement). The results in healthy controls proved that our experimental paradigm activated the expected motor and sensory networks separately using the active (motor) and passive (sensory) task. ET patients showed similar patterns of activation within the motor and sensory networks. PD patients had less activity during the active motor task in the cerebellum and basal ganglia compared to ET and healthy controls. EMG showed that in ET, tremor fluctuations correlated positively with activity in the inferior olive region, and that in PD tremor fluctuations correlated positively with cerebellar activity. Our novel approach with an MR-compatible wrist manipulator, allowed to investigate the involvement of the motor and sensory networks separately, and as such to better understand tremor pathophysiology. In ET sensorimotor network function did not differ from healthy controls. PD showed less motor-related activity. Focusing on tremor, our results indicate involvement of the inferior olive in ET tremor modulation, and cerebellar involvement in PD tremor modulation.

Brain white matter correlates of learning ankle tracking using a wearable device: importance of the superior longitudinal fasciculus II

Background

Wearable devices have been found effective in training ankle control in patients with neurological diseases. However, the neural mechanisms associated with using wearable devices for ankle training remain largely unexplored. This study aimed to investigate the ankle tracking performance and brain white matter changes associated with ankle tracking learning using a wearable-device system and the behavior–brain structure relationships in middle-aged and older adults.

Methods

Twenty-six middle-aged and older adults (48–75 years) participated in this study. Participants underwent 5-day ankle tracking learning with their non-dominant foot using a custom-built ankle tracking system equipped with a wearable sensor and a sensor-computer interface for real-time visual feedback and data acquisition. Repeated and random sequences of target tracking trajectories were both used for learning and testing. Ankle tracking performance, calculated as the root-mean-squared-error (RMSE) between the target and actual ankle trajectories, and brain diffusion spectrum MR images were acquired at baseline and retention tests. The general fractional anisotropy (GFA) values of eight brain white matter tracts of interest were calculated to indicate their integrity. Two-way (Sex × Time) mixed repeated measures ANOVA procedures were used to investigate Sex and Time effects on RMSE and GFA. Correlations between changes in RMSE and those in GFA were analyzed, controlling for age and sex.

Results

After learning, both male and female participants reduced the RMSE of tracking repeated and random sequences (both p < 0.001). Among the eight fiber tracts, the right superior longitudinal fasciculus II (R SLF II) was the only one which showed both increased GFA (p = 0.039) after learning and predictive power of reductions in RMSE for random sequence tracking with its changes in GFA [β = 0.514, R² change = 0.259, p = 0.008].

Conclusions

Our findings implied that interactive tracking movement learning using wearable sensors may place high demands on the attention, sensory feedback integration, and sensorimotor transformation functions of the brain. Therefore, the SLF II, which is known to perform these brain functions, showed corresponding neural plasticity after such learning, and its plasticity also predicted the behavioral gains. The SLF II appears to be a very important anatomical neural correlate involved in such learning paradigms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-022-01042-2.

Frequency-dependent modulation of neural oscillations across the gait cycle

Balance and walking are fundamental to support common daily activities. Relatively accurate characterizations of normal and impaired gait features were attained at the kinematic and muscular levels. Conversely, the neural processes underlying gait dynamics still need to be elucidated. To shed light on gait‐related modulations of neural activity, we collected high‐density electroencephalography (hdEEG) signals and ankle acceleration data in young healthy participants during treadmill walking. We used the ankle acceleration data to segment each gait cycle in four phases: initial double support, right leg swing, final double support, left leg swing. Then, we processed hdEEG signals to extract neural oscillations in alpha, beta, and gamma bands, and examined event‐related desynchronization/synchronization (ERD/ERS) across gait phases. Our results showed that ERD/ERS modulations for alpha, beta, and gamma bands were strongest in the primary sensorimotor cortex (M1), but were also found in premotor cortex, thalamus and cerebellum. We observed a modulation of neural oscillations across gait phases in M1 and cerebellum, and an interaction between frequency band and gait phase in premotor cortex and thalamus. Furthermore, an ERD/ERS lateralization effect was present in M1 for the alpha and beta bands, and in the cerebellum for the beta and gamma bands. Overall, our findings demonstrate that an electrophysiological source imaging approach based on hdEEG can be used to investigate dynamic neural processes of gait control. Future work on the development of mobile hdEEG‐based brain–body imaging platforms may enable overground walking investigations, with potential applications in the study of gait disorders.

Dance-based exergaming on postural stability and kinematics in people with chronic stroke - A preliminary study

INTRODUCTION

The study evaluated the feasibility, and compliance of a dance-based exergaming (DBExG) on postural stability (PS) and lower extremity (LE) kinematics, along with post-intervention changes in gait function and falls self-efficacy in people with chronic stroke (PwCS).

METHODS

Fifteen PwCS underwent DBExG for six weeks using Kinect "Just Dance 3." Pre- to post- changes were recorded during DBExG assessment on a fast-paced song (130 bpm) using an 8-camera motion capture system to assess PS (center of mass [CoM] excursions [EXs] in the anterior-posterior [AP] and mediolateral [ML] directions) and LE kinematics (hip, knee, and ankle joint angle EXs). Gait function was also assessed with gait parameters, such as gait speed, cadence, and gait symmetry on an electronic walkway. Falls self-efficacy was recorded with Falls Efficacy Scale (FES).

RESULTS

The AP and ML CoM EXs and paretic joint angle EXs significantly increased pre- to post- DBExG assessment (p < .05). Gait parameters, and falls self-efficacy measures significantly changed pre- to post- DBExG (p < .05).

CONCLUSIONS

Results exhibited the feasibility of the proposed DBExG for positively impacting postural stability, and kinematics, along with increasing gait function and falls self-efficacy among PwCS.

Multisensory integration in cortical regions responding to locomotion-related visual and somatomotor signals

During real-world locomotion, in order to be able to move along a path or avoid an obstacle, continuous changes in self-motion direction (i.e. heading) are needed. Control of heading changes during locomotion requires the integration of multiple signals (i.e., visual, somatomotor, vestibular). Recent fMRI studies have shown that both somatomotor areas (human PEc [hPEc], human PE [hPE], primary somatosensory cortex [S-I]) and egomotion visual regions (cingulate sulcus visual area [CSv], posterior cingulate area [pCi], posterior insular cortex [PIC]) respond to either leg movements and egomotion-compatible visual stimulations, suggesting a role in the analysis of both visual attributes of egomotion and somatomotor signals with the aim of guiding locomotion. However, whether these regions are able to integrate egomotion-related visual signals with somatomotor inputs coming from leg movements during heading changes remains an open question. Here we used a combined approach of individual functional localizers and task-evoked activity by fMRI. In thirty subjects we first localized three egomotion areas (CSv, pCi, PIC) and three somatomotor regions (S-I, hPE, hPEc). Then, we tested their responses in a multisensory integration experiment combining visual and somatomotor signals relevant to locomotion in congruent or incongruent trials. We used an fMR-adaptation paradigm to explore the sensitivity to the repeated presentation of these bimodal stimuli in the six regions of interest. Results revealed that hPE, S-I and CSv showed an adaptation effect regardless of congruency, while PIC, pCi and hPEc showed sensitivity to congruency. PIC exhibited a preference for congruent trials compared to incongruent trials. Areas pCi and hPEc exhibited an adaptation effect only for congruent and incongruent trials, respectively. PIC, pCi and hPEc sensitivity to the congruency relationship between visual (locomotion-compatible) cues and (leg-related) somatomotor inputs suggests that these regions are involved in multisensory integration processes, likely in order to guide/adjust leg movements during heading changes.

Tai Chi and Yoga for Improving Balance on One Leg: A Neuroimaging and Biomechanics Study

The one-leg stance is frequently used in balance training and rehabilitation programs for various balance disorders. There are some typical one-leg stance postures in Tai Chi (TC) and yoga, which are normally used for improving balance. However, the mechanism is poorly understood. Besides, the differences of one-leg stance postures between TC and yoga in training balance are still unknown. Therefore, the aim of the present study was to investigate cortical activation and rambling and trembling trajectories to elucidate the possible mechanism of improving one-leg stance balance, and compare the postural demands during one-leg stance postures between TC and yoga. Thirty-two healthy young individuals were recruited to perform two TC one-leg stance postures, i.e., right heel kick (RHK) and left lower body and stand on one leg (LSOL), two yoga postures, i.e., one-leg balance and Tree, and normal one-leg standing (OLS). Brain activation in the primary motor cortex, supplementary motor area (SMA), and dorsolateral prefrontal cortex (DLPFC) was measured using functional near-infrared spectroscopy. The center of pressure was simultaneously recorded using a force platform and decomposed into rambling and trembling components. One-way repeated-measures analysis of variance was used for the main effects. The relative concentration changes of oxygenated hemoglobin (ΔHbO) in SMA were significantly higher during RHK, LSOL, and Tree than that during OLS (p < 0.001). RHK (p < 0.001), LSOL (p = 0.003), and Tree (p = 0.006) all showed significantly larger root mean square rambling (RmRMS) than that during OLS in the medial–lateral direction. The right DLPFC activation was significantly greater during the RHK than that during the Tree (p = 0.023), OLB (p < 0.001), and OLS (p = 0.013) postures. In conclusion, the RHK, LSOL, and Tree could be used as training movements for people with impaired balance. Furthermore, the RHK in TC may provide more cognitive training in postural control than Tree and OLB in yoga. Knowledge from this study could be used and implemented in training one-leg stance balance.

EEG Synchronization-Parameters in Patients With Subcortical Arteriosclerotic Encephalopathy and Gait Disorder

PURPOSE

Subcortical arteriosclerotic encephalopathy (SAE) is characterized by extensive white matter lesions in the MRI. Clinical symptoms are cognitive impairment, ranging from mild deficits to vascular dementia, impaired executive functioning, and gait disorders. In the EEG of SAE patients with vascular dementia, the lower frequencies are increased. However, it is unclear whether EEG changes also exist in SAE patients with gait disorders but without vascular dementia.

METHODS

The authors analyzed the EEGs of 50 nondemented patients with SAE and gait disorders and 50 healthy controls applying pointwise transinformation as a measure of synchronization.

RESULTS

Hundred seconds of waking EEG that appeared unaltered in visual analysis were sufficient to prove changes in synchronization. The authors found a decrease in the mean level of synchronization, combined with an elongation of synchronization time in all examined brain areas. These effects correlated slightly with the extent of subcortical lesions.

CONCLUSIONS

Changes in EEG synchronization in patients with SAE and gait disorders seem to occur independently of cognitive function. The causal relationship of the changes in EEG synchronization and gait disorders remains to be clarified. The results of this study might point to a decrease in coupling efficiency in these patients, with the increase in synchronization duration as a possible compensatory mechanism. Because a time-efficient signal transmission particularly during gait execution is crucial, reduced efficiency might contribute to an impairment of postural stabilization. The study results might indicate a neuronal network for planning and execution of motor activity and particularly gait, extending from the frontal over the central to the parietal cortex.

Effects of augmented somatosensory input using vibratory insoles to improve walking in individuals with chronic post-stroke hemiparesis

BACKGROUND

Stroke survivors suffer from hemiparesis and somatosensory impairments, which adversely impact walking performance, placing them at higher risks for trips and falls. Post-stroke, somatosensory deficits are commonly observed as impaired interpretation of afferent input and increased threshold. Diminishing or augmenting somatosensory inputs via various techniques have been demonstrated to be able to modify static and dynamic balance, postural and locomotor control in non-neurologically impaired as well as neurologically impaired individuals.

RESEARCH QUESTION

We sought to investigate whether enhancing somatosensory input using vibratory insoles, can improve post-stroke gait. We hypothesized that with augmentation of somatosensory input at the soles via vibratory insoles would improve post-stroke gait via increased propulsive forces, decreased braking forces and increased ankle angle movements in the paretic legs of individuals with chronic post-stroke hemiparesis.

METHODS

Fifteen individuals with chronic post-stroke hemiparesis and 15 age-similar non-neurologically impaired controls participated in this cross-sectional study. Enhanced somatosensory stimulation was delivered using a pair of tactor-embedded insoles, providing suprathreshold vibratory stimulation to the bottom of the feet. Participants walked over an instrumented treadmill with self-selected speeds, under 5 conditions: no insole in shoe (NT), insoles in shoe with no vibration (BOFF), vibration under both feet (BON), vibration under one foot only (ION, CON). Kinetics and kinematics during walking were recorded and analyzed offline.

RESULTS

Suprathreshold vibratory stimulations did not alter gait kinetics under any stimulation conditions. We observed increased paretic ankle dorsiflexions in the paretic legs, when vibratory stimuli were applied unilaterally.

SIGNIFICANCE

Vibratory stimulations applied at suprathreshold intensity to the bottom of the feet to augment somatosensory feedback can potentially be used as a low-cost solution to address the inadequate toe clearance during walking in people post-stroke, which is an important goal in post-stroke rehabilitation.

Cognition mediates the relation between structural network efficiency and gait in small vessel disease

Cerebral small vessel disease (SVD), including white matter hyperintensities (WMH), microbleeds, lacunes, was related to gait disturbances, while the underlying mechanism is unclear. Here, we investigated the relation between structural network efficiency, cognition and gait performance in 272 elderly subjects with SVD. All participants underwent 1.5 T MRI, gait and neuropsychological assessment. Conventional MRI markers for SVD, i.e. WMH volume, number of lacunes and microbleeds, were assessed. Diffusion tensor imaging-based tractography was used to reconstruct the brain network for each individual, followed by graph-theoretical analyses to compute the well-established network measure, global efficiency. We found that lower global efficiency was associated with worse gait performance, including slower gait speed and shorter stride length, independent of conventional MRI markers for SVD. This association was partly mediated via cognitive function. We identified subnetworks of white matter connections associated with gait and cognition, characterized by dominant involvement of frontal tracts. Our findings suggest that network disruption is associated with gait disturbances through cognitive dysfunction in elderly with SVD. Gait is a highly cognitive process and the crucial role of cognition should be considered when investigating gait disturbances in the elderly with SVD.

Machine learning classifies predictive kinematic features in a mouse model of neurodegeneration

Motor deficits are observed in Alzheimer's disease (AD) prior to the appearance of cognitive symptoms. To investigate the role of amyloid proteins in gait disturbances, we characterized locomotion in APP-overexpressing transgenic J20 mice. We used three-dimensional motion capture to characterize quadrupedal locomotion on a treadmill in J20 and wild-type mice. Sixteen J20 mice and fifteen wild-type mice were studied at two ages (4- and 13-month). A random forest (RF) classification algorithm discriminated between the genotypes within each age group using a leave-one-out cross-validation. The balanced accuracy of the RF classification was 92.3 ± 5.2% and 93.3 ± 4.5% as well as False Negative Rate (FNR) of 0.0 ± 0.0% and 0.0 ± 0.0% for the 4-month and 13-month groups, respectively. Feature ranking algorithms identified kinematic features that when considered simultaneously, achieved high genotype classification accuracy. The identified features demonstrated an age-specific kinematic profile of the impact of APP-overexpression. Trunk tilt and unstable hip movement patterns were important in classifying the 4-month J20 mice, whereas patterns of shoulder and iliac crest movement were critical for classifying 13-month J20 mice. Examining multiple kinematic features of gait simultaneously could also be developed to classify motor disorders in humans.

Monitoring the motor cortex hemodynamic response function in freely moving walking subjects: a time-domain fNIRS pilot study

Significance: This study is a preliminary step toward the identification of a noninvasive and reliable tool for monitoring the presence and progress of gaiting dysfunctions. Aim: We present the results of a pilot study for monitoring the motor cortex hemodynamic response function (HRF) in freely walking subjects, with time-domain functional near-infrared spectroscopy (TD fNIRS). Approach: A compact and wearable single-channel TD fNIRS oximeter was employed. The lower limb motor cortex area of three healthy subjects was monitored while performing two different freely moving gaiting tasks: forward and backward walking. Results: The time course of oxygenated and deoxygenated hemoglobin was measured during the different walking tasks. Brain motor cortex hemodynamic activations have been analyzed throughout an adaptive HRF fitting procedure, showing a greater involvement of motor area in the backward walking task. By comparison with the HRF obtained in a finger-tapping task performed in a still condition, we excluded any effect of motion artifacts in the gaiting tasks. Conclusions: For the first time to our knowledge, the hemodynamic motor cortex response was measured by TD fNIRS during natural, freely walking exercises. The cortical response during forward and backward walking shows differences, possibly related to the diverse involvement of the motor cortex in the two types of gaiting.

Design and overview of the Origins of Alzheimer's Disease Across the Life course (ORACLE) study

Brain development and deterioration across the lifespan are integral to the etiology of late-life neurodegenerative disease. Factors that influence the health of the adult brain remain to be elucidated and include risk factors, protective factors, and factors related to cognitive and brain reserve. To address this knowledge gap we designed a life-course study on brain health, which received funding through the EU ERC Programme under the name Origins of Alzheimer’s Disease Across the Life course (ORACLE) Study. The ORACLE Study is embedded within Generation R, a prospective population-based cohort study of children and their parents, and links this with the Rotterdam Study, a population-based study in middle-aged and elderly persons. The studies are based in Rotterdam, the Netherlands. Generation R focuses on child health from fetal life until adolescence with repeated in-person examinations, but has also included data collection on the children’s parents. The ORACLE Study aims to extend the parental data collection in nearly 2000 parents with extensive measures on brain health, including neuroimaging, cognitive testing and motor testing. Additionally, questionnaires on migraine, depressive symptoms, sleep, and neurological family history were completed. These data allow for the investigation of longitudinal influences on adult brain health as well as intergenerational designs involving children and parents. As a secondary focus, the sampling is enriched by mothers (n = 356) that suffered from hypertensive disorders during pregnancy in order to study brain health in this high-risk population. This article provides an overview of the rationale and the design of the ORACLE Study.

Altered Cortical Reorganization and Brain Functional Connectivity in Phantom Limb Pain: A Functional MRI Study

OBJECTIVES

Functional neuroimaging studies have shown that amputees have altered cortical reorganization and functional connectivity (FC). This study aimed to investigate whether patients with phantom limb pain (PLP) and PLP-free lower limb amputees exhibit changes in corresponding primary cortical motor area/somatosensory cortex (M1/S1) cortical reorganization and supplementary motor area (SMA) network FC. The association between functional magnetic resonance imaging (fMRI) changes and clinical parameters is also explored.

METHODS

A total of 10 PLP patients were matched with 10 PLP-free amputees and 10 healthy controls (HCs). Before undergoing fMRI, all participants completed questionnaires evaluating pain, anxiety, depression, and health-related quality of life. Task-related activation and regions of interest (ROI)-wise connectivity analysis were applied to differentiate the brain regions of amputees from those of HCs. Linear correlation analysis was used to evaluate the correlation between altered FC and clinical manifestations.

RESULTS

As compared with HCs, PLP patients showed increased cortical activation in M1/S1 when moving the intact foot, imagining phantom big toe movement, or having the corresponding thumb stimulated. The increased FC in the SMA network included the SMA-caudate nucleus, SMA-bilateral insula, and SMA-anterior cingulate cortex. Furthermore, results of the linear correlation analysis demonstrated that this increased FC was positively correlated with VAS scores, negatively correlated with Medical Outcomes Study 36-item Short-Form (SF-36) scores, and not correlated with anxiety or depression scores.

CONCLUSIONS

Phantom limb pain in lower limb amputees is associated with M1/S1 cortical reorganization and altered SMA network FC in different areas of the brain, which could help to support our understanding of the central mechanism of PLP.

Evaluating a novel MR-compatible foot pedal device for unipedal and bipedal motion: Test-retest reliability of evoked brain activity

The purpose of this study was to develop and evaluate a new, open‐source MR‐compatible device capable of assessing unipedal and bipedal lower extremity movement with minimal head motion and high test–retest reliability. To evaluate the prototype, 20 healthy adults participated in two magnetic resonance imaging (MRI) visits, separated by 2–6 months, in which they performed a visually guided dorsiflexion/plantar flexion task with their left foot, right foot, and alternating feet. Dependent measures included: evoked blood oxygen level‐dependent (BOLD) signal in the motor network, head movement associated with dorsiflexion/plantar flexion, the test–retest reliability of these measurements. Left and right unipedal movement led to a significant increase in BOLD signal compared to rest in the medial portion of the right and left primary motor cortex (respectively), and the ipsilateral cerebellum (FWE corrected, p < .001). Average head motion was 0.10 ± 0.02 mm. The test–retest reliability was high for the functional MRI data (intraclass correlation coefficients [ICCs]: >0.75) and the angular displacement of the ankle joint (ICC: 0.842). This bipedal device can robustly isolate activity in the motor network during alternating plantarflexion and dorsiflexion with minimal head movement, while providing high test–retest reliability. Ultimately, these data and open‐source building instructions will provide a new, economical tool for investigators interested in evaluating brain function resulting from lower extremity movement.

Spectral Power in Marmoset Frontal Motor Cortex during Natural Locomotor Behavior

During primate arboreal locomotion, substrate orientation modifies body axis orientation and biomechanical contribution of fore- and hindlimbs. To characterize the role of cortical oscillations in integrating these locomotor demands, we recorded electrocorticographic activity from left dorsal premotor, primary motor, and supplementary motor cortices of three common marmosets moving across a branch-like small-diameter pole, fixed horizontally or vertically. Animals displayed behavioral adjustments to the task, namely, the horizontal condition mainly induced quadrupedal walk with pronated/neutral forelimb postures, whereas the vertical condition induced walk and bound gaits with supinated/neutral postures. Examination of cortical activity suggests that β (16–35 Hz) and γ (75–100 Hz) oscillations could reflect different processes in locomotor adjustments. During task, modulation of γ ERS by substrate orientation (horizontal/vertical) and epoch (preparation/execution) suggests close tuning to movement dynamics and biomechanical demands. β ERD was essentially modulated by gait (walk/bound), which could illustrate contribution to movement sequence and coordination. At rest, modulation of β power by substrate orientation underlines its role in sensorimotor processes for postural maintenance.

Brain connectivity and behavioral changes in a spaceflight analog environment with elevated CO2

Astronauts are exposed to microgravity and elevated CO₂ levels onboard the International Space Station. Little is known about how microgravity and elevated CO₂ combine to affect the brain and sensorimotor performance during and after spaceflight. Here we examined changes in resting-state functional connectivity (FC) and sensorimotor behavior associated with a spaceflight analog environment. Participants underwent 30 days of strict 6^o head-down tilt bed rest with elevated ambient CO₂ (HDBR+CO₂). Resting-state functional magnetic resonance imaging and sensorimotor assessments were collected 13 and 7 days prior to bed rest, on days 7 and 29 of bed rest, and 0, 5, 12, and 13 days following bed rest. We assessed the time course of FC changes from before, during, to after HDBR+CO₂. We then compared the observed connectivity changes with those of a HDBR control group that underwent HDBR in standard ambient air. Moreover, we assessed associations between post-HDBR+CO₂ FC changes and alterations in sensorimotor performance. HDBR+CO₂ was associated with significant changes in functional connectivity between vestibular, visual, somatosensory and motor brain areas. Several of these sensory and motor regions showed post-HDBR+CO₂ FC changes that were significantly associated with alterations in sensorimotor performance. We propose that these FC changes reflect multisensory reweighting associated with adaptation to the HDBR+CO₂ microgravity analog environment. This knowledge will further improve HDBR as a model of microgravity exposure and contribute to our knowledge of brain and performance changes during and after spaceflight.

Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness

Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

Passive, yet not inactive: robotic exoskeleton walking increases cortical activation dependent on task

Background

Experimental designs using surrogate gait-like movements, such as in functional magnetic resonance imaging (MRI), cannot fully capture the cortical activation associated with overground gait. Overground gait in a robotic exoskeleton may be an ideal tool to generate controlled sensorimotor stimulation of gait conditions like ‘active’ (i.e. user moves with the device) and ‘passive’ (i.e. user is moved by the device) gait. To truly understand these neural mechanisms, functional near-infrared spectroscopy (fNIRS) would yield greater ecological validity. Thus, the aim of this experiment was to use fNIRS to delineate brain activation differences between ‘Active’ and ‘Passive’ overground gait in a robotic exoskeleton.

Methods

Fourteen healthy adults performed 10 walking trials in a robotic exoskeleton for Passive and Active conditions, with fNIRS over bilateral frontal and parietal lobes, and electromyography (EMG) over bilateral thigh muscles. Digitization of optode locations and individual T1 MRI scans were used to demarcate the brain regions fNIRS recorded from.

Results

Increased oxyhemoglobin in the right frontal cortex was found for Passive compared with Active conditions. For deoxyhemoglobin, increased activation during Passive was found in the left frontal cortex and bilateral parietal cortices compared with Active; one channel in the left parietal cortex decreased during Active when compared with Passive. Normalized EMG mean amplitude was higher in the Active compared with Passive conditions for all four muscles (p ≤ 0.044), confirming participants produced the conditions asked of them.

Conclusions

The parietal cortex is active during passive robotic exoskeleton gait, a novel finding as research to date has not recorded posterior to the primary somatosensory cortex. Increased activation of the parietal cortex may be related to the planning of limb coordination while maintaining postural control. Future neurorehabilitation research could use fNIRS to examine whether exoskeletal gait training can increase gait-related brain activation with individuals unable to walk independently.

Modulation of Brain Functional Connectivity and Efficiency During an Endurance Cycling Task: A Source-Level EEG and Graph Theory Approach

Various methods have been employed to investigate different aspects of brain activity modulation related to the performance of a cycling task. In our study, we examined how functional connectivity and brain network efficiency varied during an endurance cycling task. For this purpose, we reconstructed EEG signals at source level: we computed current densities in 28 anatomical regions of interest (ROIs) through the eLORETA algorithm, and then we calculated the lagged coherence of the 28 current density signals to define the adjacency matrix. To quantify changes of functional network efficiency during an exhaustive cycling task, we computed three graph theoretical indices: local efficiency (LE), global efficiency (GE), and density (D) in two different frequency bands, Alpha and Beta bands, that indicate alertness processes and motor binding/fatigue, respectively. LE is a measure of functional segregation that quantifies the ability of a network to exchange information locally. GE is a measure of functional integration that quantifies the ability of a network to exchange information globally. D is a global measure of connectivity that describes the extent of connectivity in a network. This analysis was conducted for six different task intervals: pre-cycling; initial, intermediate, and final stages of cycling; and active recovery and passive recovery. Fourteen participants performed an incremental cycling task with simultaneous EEG recording and rated perceived exertion monitoring to detect the participants’ exhaustion. LE remained constant during the endurance cycling task in both bands. Therefore, we speculate that fatigue processes did not affect the segregated neural processing. We observed an increase of GE in the Alpha band only during cycling, which could be due to greater alertness processes and preparedness to stimuli during exercise. Conversely, although D did not change significantly over time in the Alpha band, its general reduction in the Beta bands during cycling could be interpreted within the framework of the neural efficiency hypothesis, which posits a reduced neural activity for expert/automated performances. We argue that the use of graph theoretical indices represents a clear methodological advancement in studying endurance performance.

Rediscovering Richard Held: Activity and Passivity in Perceptual Learning

Understanding the role of self-generated movements in perceptual learning is central to action-based theories of perception. Pioneering work on sensory adaptation by Richard M. Held during the 1950s and 1960s can still shed light on this question. In a variety of rich experiments Held and his team demonstrated the need for self-generated movements in sensory adaptation and perceptual learning. This body of work received different critical interpretations, was then forgotten for some time, and saw a surge of revived interest within embodied cognitive science. Through a brief review of Held’s work and reactions to it, we seek to contribute to discussions on the role of activity and passivity in perceptual learning. We classify different positions according to whether this role is considered to be contextual (facilitatory, but not necessary), enabling (causally necessary), or constitutive (an inextricable part of the learning process itself). We also offer a critique of the notions of activity and passivity and how they are operationalized in experimental studies. The active-passive distinction is not a binary but involves a series of dimensions and relative degrees that can make it difficult to interpret and replicate experimental results. We introduce three of these dimensions drawing on work on the sense of agency: action initiation, control, and monitoring. These refinements in terms of causal relations and dimensions of activity-passivity should help illuminate open questions concerning the role of activity in perception and perceptual learning and clarify the convergences and differences between enaction and ecological psychology.

Comparison of gait variability and symmetry in trained individuals with transtibial and transfemoral limb loss

PURPOSE

Gait variability is a determinant of qualified locomotion and is useful for monitoring the effects of therapeutic interventions. The aim of this study was to compare gait variability and symmetry in trained individuals with transtibial (TT) amputation and transfemoral (TF) amputation.

METHODS

The design of this study was planned as observational. Eleven individuals with TF amputation, 14 individuals with TT amputation, and 14 healthy individuals (HI) were evaluated with a motorized treadmill. The mean step length, the step length variability, an ambulation index, and the time on each foot (stance phase symmetry) of participants were recorded.

RESULTS

There were differences between the three groups in the residual/non-preferred limb (RNp) step length ( p = 0.031), the intact/preferred (IP) limb step length variability ( p = 0.001), the RNp step length variability ( p < 0.001), the time on each foot ( p < 0.001), and the ambulation index score ( p < 0.001). There was a similarity between the groups (TF, TT, HI) in IP limb step lengths ( p = 0.127) and duration of prosthesis usage since amputation in individuals with lower limb loss ( p = 0.224).

CONCLUSIONS

This study provided basic data about gait variability and symmetry in individuals with traumatic lower limb loss. The results of the study showed that the variability of gait increased with the level of loss, and individuals with TT amputation showed partially equivalent performance with the healthy group. Similarities in gait characteristics may have resulted from effective prosthetic usage or effective gait rehabilitation.

Motor, cognitive and mobility deficits in 1000 geriatric patients: protocol of a quantitative observational study before and after routine clinical geriatric treatment - the ComOn-study

BACKGROUND

Motor and cognitive deficits and consequently mobility problems are common in geriatric patients. The currently available methods for diagnosis and for the evaluation of treatment in this vulnerable cohort are limited. The aims of the ComOn (COgnitive and Motor interactions in the Older populatioN) study are (i) to define quantitative markers with clinical relevance for motor and cognitive deficits, (ii) to investigate the interaction between both motor and cognitive deficits and (iii) to assess health status as well as treatment outcome of 1000 geriatric inpatients in hospitals of Kiel (Germany), Brescia (Italy), Porto (Portugal), Curitiba (Brazil) and Bochum (Germany).

METHODS

This is a prospective, explorative observational multi-center study. In addition to the comprehensive geriatric assessment, quantitative measures of reduced mobility and motor and cognitive deficits are performed before and after a two week's inpatient stay. Components of the assessment are mobile technology-based assessments of gait, balance and transfer performance, neuropsychological tests, frailty, sarcopenia, autonomic dysfunction and sensation, and questionnaires to assess behavioral deficits, activities of daily living, quality of life, fear of falling and dysphagia. Structural MRI and an unsupervised 24/7 home assessment of mobility are performed in a subgroup of participants. The study will also investigate the minimal clinically relevant change of the investigated parameters.

DISCUSSION

This study will help form a better understanding of symptoms and their complex interactions and treatment effects in a large geriatric cohort.

How aging affects the premotor control of lower limb movements in simulated gait

Gait control becomes more demanding in healthy older adults, yet what cognitive or motor process leads to this age-related change is unknown. The present study aimed to investigate whether it might depend on specific decay in the quality of gait motor representation and/or a more general reduction in the efficiency of lower limb motor control. Younger and older healthy participants performed in fMRI a virtual walking paradigm that combines motor imagery (MI) of walking and standing on the spot with the presence (Dynamic Motor Imagery condition, DMI) or absence (pure MI condition) of overtly executed ankle dorsiflexion. Gait imagery was aided by the concomitant observation of moving videos simulating a stroll in the park from a first-person perspective. Behaviorally, older participants showed no sign of evident depletion in the quality of gait motor representations, and absence of between-group differences in the neural correlates of MI. However, while younger participants showed increased frontoparietal activity during DMI, older participants displayed stronger activation of premotor areas when controlling the pure execution of ankle dorsiflexion, regardless of the imagery task. These data suggest that reduced automaticity of lower limb motor control in healthy older subjects leads to the recruitment of additional premotor resources even in the absence of basic gait functional disabilities.

A Between-Subject fNIRS-BCI Study on Detecting Self-Regulated Intention During Walking

OBJECTIVE

Most BCI (brain-computer interface) studies have focused on detecting motion intention from a resting state. However, the dynamic regulation of two motion states, which usually happens in real life, is rarely studied. Besides, popular within-subject methods also require an extensive and time-consuming learning stage when testing on a new subject. This paper proposed a method to discriminate dynamic gait- adjustment intention with strong adaptability for different subjects.

METHODS

Cerebral hemoglobin signals obtained from 30 subjects were studied to decode gait-adjustment intention. Cerebral hemoglobin information was recorded by using fNIRS (functional near infrared spectroscopy) technology. Mathematical morphology filtering was applied to remove zero drift and EWM (Entropy Weight Method) was used to calculate the average hemoglobin values over Regions of Interest (ROIs). The gradient boosting decision tree (GBDT) was utilized to detect the onset of self-regulated intention. A 2-layer-GA-SVM (Genetic Algorithm-Support Vector Machine) model based on stacking algorithm was further proposed to identify the four types of self-regulated intention (speed increase, speed reduction, step increase, and step reduction).

RESULTS

It was found that GBDT had a good performance to detect the onset intention with an average AUC (Area Under Curve) of 0.894. The 2-layer-GA-SVM model boosted the average ACC (accuracy) of four types of intention from 70.6% to 84.4% ( p = 0.005 ) from the single GA-SVM model. Furthermore, the proposed method passed pseudo-online test with the average results as following: AUC = 0.883, TPR (True Positive Rate) = 97.5%, FPR (False Positive Rate) = 0.11%, and LAY (Detection Latency) = -0.52 ± 2.57 seconds for the recognition of gait-adjustment intention; ACC = 80% for the recognition of adjusted gait.

CONCLUSION

The results indicate that it is feasible to decode dynamic gait-adjustment intentions from a motion state for different subjects based on fNIRS technology. It has a potential to realize the practical application of fNIRS-based brain-computer interface technology in controlling walking-assistive devices.

Brain activity associated with Dual-task performance of Ankle motor control during cognitive challenge

INTRODUCTION

Skilled Ankle motor control is frequently required while performing secondary cognitively demanding tasks such as socializing and avoiding obstacles while walking, termed "Dual tasking." It is likely that Dual-task performance increases demand on the brain, as both motor and cognitive systems require neural resources. The purpose of this study was to use functional MRI to understand which brain regions are involved in resolving Dual-task interference created by requiring high levels of Ankle motor control during a cognitive task.

METHODS

Using functional MRI, brain activity was measured in sixteen young adults during performance of visually cued Ankle plantar flexion to a target (Ankle task), a cognitive task (Flanker task), and both tasks simultaneously (Dual task).

RESULTS

Dual-task performance did not impact the Ankle task (p = 0.78), but did affect behavior on the Flanker task. Response times for both the congruent and incongruent conditions during the Flanker task were significantly longer (p < 0.001, p = 0.050, respectively), and accuracy for the congruent condition decreased during Dual tasking (p < 0.001). Activity in 3 brain regions was associated with Dual-task Flanker performance. Percent signal change from baseline in Brodmann area (BA) 5, BA6, and the left caudate correlated with performance on the Flanker task during the Dual-task condition (R²  = 0.261, p = 0.04; R² = -0.258, p = 0.04; R²  = 0.303, p = 0.03, respectively).

CONCLUSIONS

Performance of Ankle motor control may be prioritized over a cognitive task during Dual-task performance. Our work advances Dual-task research by elucidating patterns of whole brain activity for Dual tasks that require Ankle motor control during a cognitive task.

Alterations of Functional Brain Connectivity After Long-Duration Spaceflight as Revealed by fMRI

The present study reports alterations of task-based functional brain connectivity in a group of 11 cosmonauts after a long-duration spaceflight, compared to a healthy control group not involved in the space program. To elicit the postural and locomotor sensorimotor mechanisms that are usually most significantly impaired when space travelers return to Earth, a plantar stimulation paradigm was used in a block design fMRI study. The motor control system activated by the plantar stimulation involved the pre-central and post-central gyri, SMA, SII/operculum, and, to a lesser degree, the insular cortex and cerebellum. While no post-flight alterations were observed in terms of activation, the network-based statistics approach revealed task-specific functional connectivity modifications within a broader set of regions involving the activation sites along with other parts of the sensorimotor neural network and the visual, proprioceptive, and vestibular systems. The most notable findings included a post-flight increase in the stimulation-specific connectivity of the right posterior supramarginal gyrus with the rest of the brain; a strengthening of connections between the left and right insulae; decreased connectivity of the vestibular nuclei, right inferior parietal cortex (BA40) and cerebellum with areas associated with motor, visual, vestibular, and proprioception functions; and decreased coupling of the cerebellum with the visual cortex and the right inferior parietal cortex. The severity of space motion sickness symptoms was found to correlate with a post- to pre-flight difference in connectivity between the right supramarginal gyrus and the left anterior insula. Due to the complex nature and rapid dynamics of adaptation to gravity alterations, the post-flight findings might be attributed to both the long-term microgravity exposure and to the readaptation to Earth's gravity that took place between the landing and post-flight MRI session. Nevertheless, the results have implications for the multisensory reweighting and gravitational motor system theories, generating hypotheses to be tested in future research.

Internally Guided Lower Limb Movement Recruits Compensatory Cerebellar Activity in People With Parkinson's Disease

Background: Externally guided (EG) and internally guided (IG) movements are postulated to recruit two parallel neural circuits, in which motor cortical neurons interact with either the cerebellum or striatum via distinct thalamic nuclei. Research suggests EG movements rely more heavily on the cerebello-thalamo-cortical circuit, whereas IG movements rely more on the striato-pallido-thalamo-cortical circuit (1). Because Parkinson's (PD) involves striatal dysfunction, individuals with PD have difficulty generating IG movements (2).

Objectives: Determine whether individuals with PD would employ a compensatory mechanism favoring the cerebellum over the striatum during IG lower limb movements.

Methods: 22 older adults with mild-moderate PD, who had abstained at least 12 h from anti-PD medications, and 19 age-matched controls performed EG and IG rhythmic foot-tapping during functional magnetic resonance imaging. Participants with PD tapped with their right (more affected) foot. External guidance was paced by a researcher tapping participants' ipsilateral 3rd metacarpal in a pattern with 0.5 to 1 s intervals, while internal guidance was based on pre-scan training in the same pattern. BOLD activation was compared between tasks (EG vs. IG) and groups (PD vs. control).

Results: Both groups recruited the putamen and cerebellar regions. The PD group demonstrated less activation in the striatum and motor cortex than controls. A task (EG vs. IG) by group (PD vs. control) interaction was observed in the cerebellum with increased activation for the IG condition in the PD group.

Conclusions: These findings support the hypothesized compensatory shift in which the dysfunctional striatum is assisted by the less affected cerebellum to accomplish IG lower limb movement in individuals with mild-moderate PD. These findings are of relevance for temporal gait dysfunction and freezing of gait problems frequently noted in many people with PD and may have implications for future therapeutic application.

Increased Insular Connectivity and Enhanced Empathic Ability Associated with Dance/Music Training

Dance and music are expressive art forms. Previous behavioural studies have reported that dancers/musicians show a better sensorimotor ability and emotional representation of others. However, the neural mechanism behind this phenomenon is not completely understood. Recently, intensive researches have identified that the insula is highly enrolled in the empathic process. Thus, to expand the knowledge of insular function associated with empathy under the dance/music training background, we mapped the insular network and its associated brain regions in 21 dancers, 20 musicians, and 24 healthy controls using resting-state functional connectivity (FC) analysis. Whole brain voxel-based analysis was performed using seeds from the posterior insula (PI), the ventral anterior insula (vAI), and the dorsal anterior insula (dAI). The training effects of dance and music on insular subnetworks were then evaluated using one-way analysis of variance ANOVA. Increased insular FC with those seeds was found in dancers/musicians, including PI and anterior cingulated cortex (ACC), vAI and middle temporal gyrus (MTG) and middle cingulated cortex (MCC), and dAI and ACC and MTG. In addition, significant associations were found between discrepant insular FC patterns and empathy scores in dancers and musicians. These results indicated that dance/music training might enhance insular subnetwork function, which would facilitate integration of intero/exteroceptive information and result in better affective sensitivity. Those changes might finally facilitate the subjects' empathic ability.

EEG time-frequency analysis provides arguments for arm swing support in human gait control

BACKGROUND

Human gait benefits from arm swing, which requires four-limb co-ordination. The Supplementary Motor Area (SMA) is involved in multi-limb coordination. With its location anterior to the leg motor cortex and the pattern of its connections, this suggests a distinct role in gait control.

RESEARCH QUESTION

Is the SMA functionally implicated in gait-related arm swing?

METHODS

Ambulant electroencephalography (EEG) was employed during walking with and without arm swing in twenty healthy subjects (mean age: 64.9yrs, SD 7.2). Power changes across the EEG frequency spectrum were assessed by Event Related Spectral Perturbation (ERSP) analysis over both the putative SMA at electrode position Fz and additional sensorimotor regions.

RESULTS

During walking with arm swing, midline electrodes Fz and Cz showed a step-related pattern of Event Related Desynchronization (ERD) followed by Event Related Synchronization (ERS). Walking without arm swing was associated with significant ERD-ERS power reduction in the high-beta/low-gamma band over Fz and a power increase over Cz. Electrodes C3 and C4 revealed a pattern of ERD during contralateral- and ERS during ipsilateral leg swing. This ERD power decreased in gait without arm swing (low-frequency band). The ERSP pattern during walking with arm swing was similar at CP1 and CP2: ERD was seen during double support and the initial swing phase of the right leg, while a strong ERS emerged during the second half of the left leg's swing. Walking without arm swing showed a significant power reduction of this ERD-ERS pattern over CP2, while over CP1, ERS during left leg's swing turned into ERD.

CONCLUSION

The relation between arm swing in walking and a step-related ERD-ERS pattern in the high-beta/low-gamma band over the putative SMA, points at an SMA contribution to integrated cyclic anti-phase movements of upper- and lower limbs. This supports a cortical underpinning of arm swing support in gait control.

Egomotion-related visual areas respond to active leg movements

Monkey neurophysiology and human neuroimaging studies have demonstrated that passive viewing of optic flow stimuli activates a cortical network of temporal, parietal, insular, and cingulate visual motion regions. Here, we tested whether the human visual motion areas involved in processing optic flow signals simulating self-motion are also activated by active lower limb movements, and hence are likely involved in guiding human locomotion. To this aim, we used a combined approach of task-evoked activity and resting-state functional connectivity by fMRI. We localized a set of six egomotion-responsive visual areas (V6+, V3A, intraparietal motion/ventral intraparietal [IPSmot/VIP], cingulate sulcus visual area [CSv], posterior cingulate sulcus area [pCi], posterior insular cortex [PIC]) by using optic flow. We tested their response to a motor task implying long-range active leg movements. Results revealed that, among these visually defined areas, CSv, pCi, and PIC responded to leg movements (visuomotor areas), while V6+, V3A, and IPSmot/VIP did not (visual areas). Functional connectivity analysis showed that visuomotor areas are connected to the cingulate motor areas, the supplementary motor area, and notably to the medial portion of the somatosensory cortex, which represents legs and feet. We suggest that CSv, pCi, and PIC perform the visual analysis of egomotion-like signals to provide sensory information to the motor system with the aim of guiding locomotion.

FDG PET Findings according to Wandering Patterns of Patients with Drug-naïve Alzheimer's Disease

Background and Purpose

To explore anatomic substrate of specific wandering patterns in patients with Alzheimer's disease (AD) by performing positron emission tomography with ¹⁸F fluorodeoxyglucose positron emission tomography (FDG PET).

Methods

Drug-naïve AD patients with wandering (n=80) and without wandering (n=262) were recruited. First, the specific pattern of wandering type was operationally classified according to specific wandering score and clinical assessment. Second, brain FDG PET was performed and fluorodeoxyglucose (FDG) uptake differences of specific brain regions according to wandering patterns were compared to those of non-wanderers.

Results

In patients with pacing pattern, FDG PET showed significant lower FDG uptake in both middle cingulum and left putamen cluster compared to non-wanderers. The right precuneus and supplementary motor area in patients with random pattern and left calcarine sulcus, right calcarine sulcus, right middle cingulum, and right post central gyrus in patients with lapping pattern had significantly lower FDG uptake compared to non-wanderers.

Conclusions

This study showed that wandering in patients with AD had three distinct patterns. These specific patterns showed significant lower FDG uptake in specific brain areas compared to non-wanderers.

Design of a low-cost MRI compatible plantarflexion force measurement device

Investigating the neural correlates of ankles' joint rotation is critical to better understand the underlying deficit in balance or posture control in the clinical population. This work describes the design and characteristics of a low-cost MRI compatible isometric plantarflexion force measurement device. The device is fully adjustable to the particular height and shoe size of participants. Each individual force sensor has an operational linear range up to 80-100kg amounting to a force range up to 180kg when combining the two sensors, which is well above the maximal force for the majority of the population. Preliminary neuroimaging tests suggest that performing submaximal ankle plantar flexions on the device induce minimal motion artifacts on fMRI signal that are within an acceptable range.

Brain Functional Connectivity Plasticity Within and Beyond the Sensorimotor Network in Lower-Limb Amputees

Cerebral neuroplasticity after amputation has been elucidated by functional neuroimaging. However, little is known concerning how brain network-level functional reorganization of the sensorimotor system evolves following lower-limb amputation. We studied 32 unilateral lower-limb amputees (LLAs) and 32 matched healthy controls (HCs) using resting-state functional magnetic resonance imaging (rs-fMRI). A regions of interest (ROI)-wise connectivity analysis was performed with ROIs in eight brain regions in the sensorimotor network to investigate intra-network changes, and seed-based whole-brain functional connectivity (FC) with a seed in the contralateral primary sensorimotor cortex (S1M1) was used to study the FC reorganization between the sensorimotor region (S1M1) and other parts of the brain in the LLAs. The ROI-wise connectivity analysis showed that the LLAs had decreased FC, mainly between the subcortical nuclei and the contralateral S1M1 (p < 0.05, FDR corrected). Seed-based whole-brain FC analysis revealed that brain regions with decreased FC with the contralateral S1M1 extended beyond the sensorimotor network to the prefrontal and visual cortices (p < 0.05, FDR corrected). Moreover, correlation analysis showed that decreased FC between the subcortical and the cortical regions in the sensorimotor network progressively increased in relation to the time since amputation. These findings indicated a cascade of cortical reorganization at a more extensive network level following lower-limb amputation, and also showed promise for the development of a possible neurobiological marker of changes in FC related to motor function recovery in LLAs.

Neural correlates of lower limbs proprioception: An fMRI study of foot position matching

Little is known about the neural correlates of lower limbs position sense, despite the impact that proprioceptive deficits have on everyday life activities, such as posture and gait control. We used fMRI to investigate in 30 healthy right-handed and right-footed subjects the regional distribution of brain activity during position matching tasks performed with the right dominant and the left nondominant foot. Along with the brain activation, we assessed the performance during both ipsilateral and contralateral matching tasks. Subjects had lower errors when matching was performed by the left nondominant foot. The fMRI analysis suggested that the significant regions responsible for position sense are in the right parietal and frontal cortex, providing a first characterization of the neural correlates of foot position matching.

Effects of tDCS on Real-Time BCI Detection of Pedaling Motor Imagery

The purpose of this work is to strengthen the cortical excitability over the primary motor cortex (M1) and the cerebro-cerebellar pathway by means of a new transcranial direct current stimulation (tDCS) configuration to detect lower limb motor imagery (MI) in real time using two different cognitive neural states: relax and pedaling MI. The anode is located over the primary motor cortex in Cz, and the cathode over the right cerebro-cerebellum. The real-time brain-computer interface (BCI) designed is based on finding, for each electrode selected, the power at the particular frequency where the most difference between the two mental tasks is observed. Electroencephalographic (EEG) electrodes are placed over the brain's premotor area (PM), M1, supplementary motor area (SMA) and primary somatosensory cortex (S1). A single-blind study is carried out, where fourteen healthy subjects are separated into two groups: sham and active tDCS. Each subject is experimented on for five consecutive days. On all days, the results achieved by the active tDCS group were over 60% in real-time detection accuracy, with a five-day average of 62.6%. The sham group eventually reached those levels of accuracy, but it needed three days of training to do so.

Assessment of user voluntary engagement during neurorehabilitation using functional near-infrared spectroscopy: a preliminary study

BACKGROUND

Functional near infrared spectroscopy (fNIRS) finds extended applications in a variety of neuroscience fields. We investigated the potential of fNIRS to monitor voluntary engagement of users during neurorehabilitation, especially during combinatory exercise (CE) that simultaneously uses both, passive and active exercises. Although the CE approach can enhance neurorehabilitation outcome, compared to the conventional passive or active exercise strategies, the active engagement of patients in active motor movements during CE is not known.

METHODS

We determined hemodynamic responses induced by passive exercise and CE to evaluate the active involvement of users during CEs using fNIRS. In this preliminary study, hemodynamic responses of eight healthy subjects during three different tasks (passive exercise alone, passive exercise with motor imagery, and passive exercise with active motor execution) were recorded. On obtaining statistically significant differences, we classified the hemodynamic responses induced by passive exercise and CEs to determine the identification accuracy of the voluntary engagement of users using fNIRS.

RESULTS

Stronger and broader activation around the sensorimotor cortex was observed during CEs, compared to that during passive exercise. Moreover, pattern classification results revealed more than 80% accuracy.

CONCLUSIONS

Our preliminary study demonstrated that fNIRS can be potentially used to assess the engagement of users of the combinatory neurorehabilitation strategy.

Comparison of Gait Parameters for Predicting Cognitive Decline: The Mayo Clinic Study of Aging

BACKGROUND

Previous studies reported that slower gait speed might predict cognitive impairment and dementing illnesses, supporting the role of gait speed as a possible subclinical marker of cognitive impairment. However, the predictive value of other gait parameters for cognitive decline is unclear.

OBJECTIVE

To investigate and compare the association with, and prediction of, specific gait parameters for cognition in a population-based sample.

METHODS

The analysis included 3,426 cognitively normal participants enrolled in the Mayo Clinic Study of Aging. At baseline and every 15 months (mean follow-up = 1.93 years), participants had a study coordinator evaluation, neurological examination, and a neuropsychological assessment using nine tests that covered four domains. Gait parameters were assessed with the GAITRite® instrument. General linear mixed effects models were used to compute the annualized rate of change in cognitive domain z-scores, controlling for age, sex, education, depression, comorbidities, body mass index, APOE ɛ4 allele, and visit number, and excluding individuals with a history of stroke, alcoholism, Parkinson's disease, subdural hematoma, and normal pressure hydrocephalus.

RESULTS

Spatial (stride length), temporal (ambulatory time, gait speed, step count, cadence, double support time), and spatiotemporal (cadence) gait parameters, and greater intraindividual variability in stride length, swing time, and stance time were associated with a significant decline in global cognition and in specific domains including memory, executive function, visuospatial, and language.

CONCLUSIONS

Spatial, temporal, and spatiotemporal measures of gait and greater variability of gait parameters were associated with and predictive of both global- and domain-specific cognitive decline.

Optimization of fMRI methods to determine laterality of cortical activation during ankle movements of children with unilateral cerebral palsy

Measurement of laterality of motor cortical activations may provide valuable information about lower limb control in children with unilateral cerebral palsy (UCP). Evidence from upper limb research suggests that increased contralateral activity may accompany functional gains. However, lower limb areas of activation and associated changes have been underexplored due to challenges with imaging motor cortical leg representations. In this study, methods for a task-based functional magnetic resonance imaging (fMRI) ankle dorsiflexion paradigm were refined with three pilot groups of participants: (i) adults (n = 5); (ii) typically developing (TD) children (n = 5) and; (iii) children with UCP (n = 4). Parameters of experimental design, task resistance, reproducibility, and pre-scan procedures were tested/refined using a staged development approach with additions or changes introduced if image quality did not meet pre-defined standards. When image quality was acceptable for two consecutive participants, the next participant group was recruited to test/refine the next parameter. The final paradigm involved an event-related design of a single dorsiflexion movement against individualized resistance, with two runs per leg. It included a pre-scan session to increase child comfort and determine task resistance. This paradigm produced valid data for laterality index (LI) calculations to determine the ratio of activity in each hemisphere. Ventricle and lesion masks were used in non-linear image registration, and individual thresholds were used for extent-based LI calculations. LI of dominant ankle movements were contralateral (LI ≥ +0.2) for TD children (mean LI = +0.89, std = 0.27) and children with UCP (mean LI = +0.86, std = 0.26). For the affected ankle of children with UCP, LI values indicated ipsilateral and/or contralateral activation (mean LI = +0.02, std = 0.71, range -0.92 to +1.00). This fMRI paradigm will support investigations of cortical activation and mechanisms of skill improvement following lower limb interventions.