Cortical mapping of gait in humans: a near-infrared spectroscopic topography study

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Evidence for Differential Effects of 2 Forms of Exercise on Prefrontal Plasticity During Walking in Parkinson's Disease

BACKGROUND

In a randomized control trial conducted in patients with Parkinson's disease, a treadmill training program combined with virtual reality that targeted motor and cognitive aspects of safe ambulation led to fewer falls, compared with treadmill training alone.

OBJECTIVE

To investigate if the 2 types of training differentially affected prefrontal activation and if this might explain differences in fall rates after the intervention.

METHODS

Sixty-four patients with Parkinson's disease were randomized into the treadmill training arm (n = 34, mean age 73.1 ± 1.1 years, 64% men, disease duration 9.7 ± 1.0 years) or treadmill training with virtual reality arm (n = 30, mean age 70.1 ± 1.3 years, 71% men, disease duration 8.9 ± 1.1 years). Prefrontal activation during usual, dual-task, and obstacle negotiation walking was assessed before and after 6 weeks of training, using a functional near-infrared spectroscopy system.

RESULTS

Treadmill training with and without virtual reality reduced prefrontal activation during walking ( P < .001), with specific interactions related to training arm ( P = .01), lateralization ( P = .05), and walking condition ( P = .001). For example, among the subjects who trained with treadmill training alone, prefrontal activation during dual-task walking and obstacle negotiation increased after training, while in the combined training arm, activation decreased.

CONCLUSIONS

Prefrontal activation during usual and during more challenging walking conditions can be altered in response to 2 different types of training. The addition of a cognitive training component to a treadmill exercise program apparently modifies the effects of the training on the magnitude and lateralization of prefrontal activation and on falls, extending the understanding of the plasticity of the brain in PD.

Functional near-infrared spectroscopy during optic flow with and without fixation

BACKGROUND AND PURPOSE

Individuals with visual vertigo describe symptoms of dizziness, disorientation, and/or impaired balance in environments with conflicting visual and vestibular information or complex visual stimuli. Physical therapists often prescribe habituation exercises using optic flow to treat these symptoms, but there are no evidence-based guidelines for delivering optic flow and it is unclear how the brain processes such stimuli. The purposes of this study were to use functional near-infrared spectroscopy (fNIRS) to explore cerebral activation during optic flow, and determine if visual fixation had a modulating effect on brain activity.

METHODS

Fifteen healthy participants (7 males and 8 females; mean age 41 years old) stood in a virtual reality environment and viewed optic flow moving unidirectionally in the yaw plane with and without fixation. Changes in cerebral activation were recorded from the bilateral fronto-temporo-parietal and occipital lobes using fNIRS.

RESULTS

Cerebral activation was greater with visual motion than while viewing a stationary scene. Greater cerebral activation in the bilateral fronto-temporo-parietal lobes was observed when optic flow was viewed with fixation.

DISCUSSION AND CONCLUSIONS

Optic flow activates the bilateral fronto-temporo-parietal regions of the cerebral cortex. This activation is greater while viewing optic flow and a fixation target, providing preliminary evidence supporting the use of a fixation target during habituation exercises.

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.

fNIRS-based Neurorobotic Interface for gait rehabilitation

BACKGROUND

In this paper, a novel functional near-infrared spectroscopy (fNIRS)-based brain-computer interface (BCI) framework for control of prosthetic legs and rehabilitation of patients suffering from locomotive disorders is presented.

METHODS

fNIRS signals are used to initiate and stop the gait cycle, while a nonlinear proportional derivative computed torque controller (PD-CTC) with gravity compensation is used to control the torques of hip and knee joints for minimization of position error. In the present study, the brain signals of walking intention and rest tasks were acquired from the left hemisphere's primary motor cortex for nine subjects. Thereafter, for removal of motion artifacts and physiological noises, the performances of six different filters (i.e. Kalman, Wiener, Gaussian, hemodynamic response filter (hrf), Band-pass, finite impulse response) were evaluated. Then, six different features were extracted from oxygenated hemoglobin signals, and their different combinations were used for classification. Also, the classification performances of five different classifiers (i.e. k-Nearest Neighbour, quadratic discriminant analysis, linear discriminant analysis (LDA), Naïve Bayes, support vector machine (SVM)) were tested.

RESULTS

The classification accuracies obtained from SVM using the hrf were significantly higher (p < 0.01) than those of the other classifier/ filter combinations. Those accuracies were 77.5, 72.5, 68.3, 74.2, 73.3, 80.8, 65, 76.7, and 86.7% for the nine subjects, respectively.

CONCLUSION

The control commands generated using the classifiers initiated and stopped the gait cycle of the prosthetic leg, the knee and hip torques of which were controlled using the PD-CTC to minimize the position error. The proposed scheme can be effectively used for neurofeedback training and rehabilitation of lower-limb amputees and paralyzed patients.

Cortical Oxyhemoglobin Elevation Persists After Moderate-Intensity Cycling Exercise: A Near-Infrared Spectroscopy Study

Near-infrared spectroscopy (NIRS) can measure cortical activity during gross motor tasks based on the cerebral hemodynamic response. Although some reports suggest that cycling exercise improves cortical oxygenation, its after-effects are unknown. We examined the after-effects of low- and moderate-intensity cycling exercise on cortical oxygenation. Ten healthy volunteers (mean age 21.3 ± 0.7 years; 4 women) underwent cycle ergometer exercise at 30% or 50% of VO₂peak for 20 min, followed by an 8-min post-exercise rest (PER). O₂Hb levels of the supplementary motor area (SMA) and sensorimotor cortex (SMC) were recorded using a near-infrared spectroscopy system. Skin blood flow (SBF) and mean arterial pressure (MAP) were continuously measured. The peak values of O₂Hb between exercise and PER were compared. The O₂Hb, SBF, and MAP increased in the exercise phase. SBF degraded over time, and MAP decreased immediately after exercise. The O₂Hb decreased immediately and increased again in the PER. There were no significant differences between exercise and PER in the SMC in the 30% VO₂peak experiment or in the SMA and SMC in the 50% VO₂peak experiment. The O₂Hb in the motor-related area was elevated during both exercise and PER especially in the 50% VO₂peak experiment.

Signal Processing in Functional Near-Infrared Spectroscopy (fNIRS): Methodological Differences Lead to Different Statistical Results

Even though research in the field of functional near-infrared spectroscopy (fNIRS) has been performed for more than 20 years, consensus on signal processing methods is still lacking. A significant knowledge gap exists between established researchers and those entering the field. One major issue regularly observed in publications from researchers new to the field is the failure to consider possible signal contamination by hemodynamic changes unrelated to neurovascular coupling (i.e., scalp blood flow and systemic blood flow). This might be due to the fact that these researchers use the signal processing methods provided by the manufacturers of their measurement device without an advanced understanding of the performed steps. The aim of the present study was to investigate how different signal processing approaches (including and excluding approaches that partially correct for the possible signal contamination) affect the results of a typical functional neuroimaging study performed with fNIRS. In particular, we evaluated one standard signal processing method provided by a commercial company and compared it to three customized approaches. We thereby investigated the influence of the chosen method on the statistical outcome of a clinical data set (task-evoked motor cortex activity). No short-channels were used in the present study and therefore two types of multi-channel corrections based on multiple long-channels were applied. The choice of the signal processing method had a considerable influence on the outcome of the study. While methods that ignored the contamination of the fNIRS signals by task-evoked physiological noise yielded several significant hemodynamic responses over the whole head, the statistical significance of these findings disappeared when accounting for part of the contamination using a multi-channel regression. We conclude that adopting signal processing methods that correct for physiological confounding effects might yield more realistic results in cases where multi-distance measurements are not possible. Furthermore, we recommend using manufacturers' standard signal processing methods only in case the user has an advanced understanding of every signal processing step performed.

Changes in Cerebral Oxyhaemoglobin Levels During and After a Single 20-Minute Bout of Moderate-Intensity Cycling

Aerobic exercise produces changes in cerebral oxyhaemoglobin (O₂Hb) concentration; however, the effects of exercise on O₂Hb during the post-exercise period remain to be established. The aim of the present study was to evaluate O₂Hb levels during and after a 20-min bout of moderate-intensity cycling exercise. After a 3-min rest period, 12 healthy volunteers (9 women, 3 men) cycled for 20 min at an intensity corresponding to 50% of their VO₂max, after which they were monitored during a 15-min post-exercise rest period. O₂Hb levels in the right (R-PFC) and left prefrontal cortices (L-PFC), right (R-PMA) and left premotor areas (L-PMA), supplementary motor area (SMA), and primary motor cortex (M1) were measured using near-infrared spectroscopy. A one-way repeated-measures analysis of variance (ANOVA) was performed to compare mean pre-exercise O₂Hb levels with O₂Hb levels during the last 5 min of exercise and the last 5 min of the post-exercise rest period. O₂Hb levels increased significantly (p < 0.01) between the pre-exercise rest period and the last 5 min of the exercise session for each region of interest (range: 0.040-0.085 mM·cm). O₂Hb levels did not return to pre-exercise values during the 15-min post-exercise rest period. O₂Hb levels during the last 5 min of the post-exercise rest period were significantly higher than pre-exercise values in the L-PFC, L-PMA, SMA, and M1 (p < 0.01). Our results indicate that cortical oxygenation persists for at least 15 min following a 20-min bout of moderate-intensity cycling, and that aerobic exercise may facilitate neuroplasticity.

Electrocortical correlates of human level-ground, slope, and stair walking

This study investigated electrocortical dynamics of human walking across different unconstrained walking conditions (i.e., level ground (LW), ramp ascent (RA), and stair ascent (SA)). Non-invasive active-electrode scalp electroencephalography (EEG) signals were recorded and a systematic EEG processing method was implemented to reduce artifacts. Source localization combined with independent component analysis and k-means clustering revealed the involvement of four clusters in the brain during the walking tasks: Left and Right Occipital Lobe (LOL, ROL), Posterior Parietal Cortex (PPC), and Central Sensorimotor Cortex (SMC). Results showed that the changes of spectral power in the PPC and SMC clusters were associated with the level of motor task demands. Specifically, we observed α and β suppression at the beginning of the gait cycle in both SA and RA walking (relative to LW) in the SMC. Additionally, we observed significant β rebound (synchronization) at the initial swing phase of the gait cycle, which may be indicative of active cortical signaling involved in maintaining the current locomotor state. An increase of low γ band power in this cluster was also found in SA walking. In the PPC, the low γ band power increased with the level of task demands (from LW to RA and SA). Additionally, our results provide evidence that electrocortical amplitude modulations (relative to average gait cycle) are correlated with the level of difficulty in locomotion tasks. Specifically, the modulations in the PPC shifted to higher frequency bands when the subjects walked in RA and SA conditions. Moreover, low γ modulations in the central sensorimotor area were observed in the LW walking and shifted to lower frequency bands in RA and SA walking. These findings extend our understanding of cortical dynamics of human walking at different level of locomotion task demands and reinforces the growing body of literature supporting a shared-control paradigm between spinal and cortical networks during locomotion.

Cortical activation pattern during shoulder simple versus vibration exercises: a functional near infrared spectroscopy study

To date, the cortical effect of exercise has not been fully elucidated. Using the functional near infrared spectroscopy, we attempted to compare the cortical effect between shoulder vibration exercise and shoulder simple exercise. Eight healthy subjects were recruited for this study. Two different exercise tasks (shoulder vibration exercise using the flexible pole and shoulder simple exercise) were performed using a block paradigm. We measured the values of oxygenated hemoglobin in the four regions of interest: the primary sensory-motor cortex (SM1 total, arm somatotopy, and leg and trunk somatotopy), the premotor cortex, the supplementary motor area, and the prefrontal cortex. During shoulder vibration exercise and shoulder simple exercise, cortical activation was observed in SM1 (total, arm somatotopy, and leg and trunk somatotopy), premotor cortex, supplementary motor area, and prefrontal cortex. Higher oxygenated hemoglobin values were also observed in the areas of arm somatotopy of SM1 compared with those of other regions of interest. However, no significant difference in the arm somatotopy of SM1 was observed between the two exercises. By contrast, in the leg and trunk somatotopy of SM1, shoulder vibration exercise led to a significantly higher oxy-hemoglobin value than shoulder simple exercise. These two exercises may result in cortical activation effects for the motor areas relevant to the shoulder exercise, especially in the arm somatotopy of SM1. However, shoulder vibration exercise has an additional cortical activation effect for the leg and trunk somatotopy of SM1.

Neural correlates of obstacle negotiation in older adults: An fNIRS study

Older adults are less efficient at avoiding obstacles compared to young adults, especially under attention-demanding conditions. Using functional near-infrared-spectroscopy (fNIRS), recent studies implicated the prefrontal cortex (PFC) in cognitive control of locomotion, notably under dual-task walking conditions. The neural substrates underlying Obstacle Negotiation (ON), however, have not been established. The current study determined the role of the PFC in ON during walking in seniors. Non-demented older adults (n=90; mean age=78.1±5.5years; %female=51) underwent fNIRS acquisition to assess changes in hemodynamic activity in the PFC during normal-walk [NW] and walk-while-talk [WWT] conditions with and without obstacles. Obstacles were presented as red elliptical shapes using advanced laser technology, which resemble potholes. Linear mixed effects models were used to determine differences in oxygenated hemoglobin (HbO₂) levels among the four task conditions. The presence of slow gait, a risk factor for dementia and falls, served as a predictor hypothesized to moderate the effect of obstacles on PFC HbO₂ levels. PFC HbO₂ levels were significantly higher in WWT compared to NW (p<0.001) irrespective of ON. Slow gait moderated the effect of obstacles on HbO₂ levels across task conditions. Specifically, compared to participants with normal gait, PFC HbO₂ levels were significantly increased in ON-NW relative to NW (p=0.017) and ON-WWT relative to WWT (p<0.001) among individuals with slow gait. Consistent with Compensatory Reallocation, ON required greater PFC involvement among individuals with mobility limitations.

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

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

Neurofeedback-induced facilitation of the supplementary motor area affects postural stability

Near-infrared spectroscopy-mediated neurofeedback (NIRS-NFB) is a promising therapeutic intervention for patients with neurological diseases. Studies have shown that NIRS-NFB can facilitate task-related cortical activation and induce task-specific behavioral changes. These findings indicate that the effect of neuromodulation depends on local cortical function. However, when the target cortical region has multiple functions, our understanding of the effects is less clear. This is true in the supplementary motor area (SMA), which is involved both in postural control and upper-limb movement. To address this issue, we investigated the facilitatory effect of NIRS SMA neurofeedback on cortical activity and behavior, without any specific task. Twenty healthy individuals participated in real and sham neurofeedback. Balance and hand dexterity were assessed before and after each NIRS-NFB session. We found a significant interaction between assessment periods (pre/post) and condition (real/sham) with respect to balance as assessed by the center of the pressure path length but not for hand dexterity as assessed by the 9-hole peg test. SMA activity only increased during real neurofeedback. Our findings indicate that NIRS-NFB itself has the potential to modulate focal cortical activation, and we suggest that it be considered a therapy to facilitate the SMA for patients with postural impairment.

Neural Correlates of Single- and Dual-Task Walking in the Real World

Recent developments in mobile brain-body imaging (MoBI) technologies have enabled studies of human locomotion where subjects are able to move freely in more ecologically valid scenarios. In this study, MoBI was employed to describe the behavioral and neurophysiological aspects of three different commonly occurring walking conditions in healthy adults. The experimental conditions were self-paced walking, walking while conversing with a friend and lastly walking while texting with a smartphone. We hypothesized that gait performance would decrease with increased cognitive demands and that condition-specific neural activation would involve condition-specific brain areas. Gait kinematics and high density electroencephalography (EEG) were recorded whilst walking around a university campus. Conditions with dual tasks were accompanied by decreased gait performance. Walking while conversing was associated with an increase of theta (θ) and beta (β) neural power in electrodes located over left-frontal and right parietal regions, whereas walking while texting was associated with a decrease of β neural power in a cluster of electrodes over the frontal-premotor and sensorimotor cortices when compared to walking whilst conversing. In conclusion, the behavioral “signatures” of common real-life activities performed outside the laboratory environment were accompanied by differing frequency-specific neural “biomarkers”. The current findings encourage the study of the neural biomarkers of disrupted gait control in neurologically impaired patients.

Contralesional Hemisphere Regulation of Transcranial Magnetic Stimulation-Induced Kinetic Coupling in the Poststroke Lower Limb

BACKGROUND

The neural constraints underlying hemiparetic gait dysfunction are associated with abnormal kinetic outflow and altered muscle synergy structure. Recent evidence from our lab implicates the lesioned hemisphere in mediating the expression of abnormally coupled hip adduction and knee extension synergy, suggesting a role of cortical networks in the regulation of lower limb motor outflow poststroke. The potential contribution of contralesional hemisphere (CON-H) in regulating paretic leg kinetics is unknown. The purpose of this study is to characterize the effect of CON-H activation on aberrant across-joint kinetic coupling of the ipsilateral lower-extremity muscles poststroke.

METHODS

Amplitude-matched adductor longus motor-evoked potentials were elicited using single pulse transcranial magnetic stimulation (TMS) of the lesioned (L-H) and CON-Hs during an isometric adductor torque matching task from 11 stroke participants. For 10 control participants, TMS of the contralateral and ipsilateral hemisphere were given during the same task. TMS-induced torques were characterized at the hip and knee joints to determine the differential regulation of abnormal kinetic synergies by each motor cortices. The TMS-induced ratio of knee extension/hip adduction torques was quantified during 40 and 20% of maximum adduction torque.

FINDINGS

For both the 40 and 20% target adduction tasks, we find that contralesional stimulation significantly reduced but did not eliminate the TMS-induced ratio of knee extension/hip adduction torques for the stroke group (p = 0.0468, p = 0.0396). In contrast, the controls did not present a significantly different TMS-evoked torque following stimulation (p = 0.923) of the hemisphere ipsilateral to the test leg.

INTERPRETATION

The reduced expression of abnormal across-joint kinetic coupling suggests that the CON-H may contribute an adaptive role in lower limb control poststroke. Future study of neuromodulation paradigms that leverage adaptive CON-H activation may yield clinically relevant gains in lower limb motor function poststroke.

Unidirectional brain to muscle connectivity reveals motor cortex control of leg muscles during stereotyped walking

In lower mammals, locomotion seems to be mainly regulated by subcortical and spinal networks. On the contrary, recent evidence suggests that in humans the motor cortex is also significantly engaged during complex locomotion tasks. However, a detailed understanding of cortical contribution to locomotion is still lacking especially during stereotyped activities. Here, we show that cortical motor areas finely control leg muscle activation during treadmill stereotyped walking. Using a novel technique based on a combination of Reliable Independent Component Analysis, source localization and effective connectivity, and by combining electroencephalographic (EEG) and electromyographic (EMG) recordings in able-bodied adults we were able to examine for the first time cortical activation patterns and cortico-muscular connectivity including information flow direction. Results not only provided evidence of cortical activity associated with locomotion, but demonstrated significant causal unidirectional drive from contralateral motor cortex to muscles in the swing leg. These insights overturn the traditional view that human cortex has a limited role in the control of stereotyped locomotion, and suggest useful hypotheses concerning mechanisms underlying gait under other conditions.

ONE SENTENCE SUMMARY

Motor cortex proactively drives contralateral swing leg muscles during treadmill walking, counter to the traditional view of stereotyped human locomotion.

Mental steps: Differential activation of internal pacemakers in motor imagery and in mental imitation of gait

Gait imagery and gait observation can boost the recovery of locomotion dysfunctions; yet, a neurologically justified rationale for their clinical application is lacking as much as a direct comparison of their neural correlates. Using functional magnetic resonance imaging, we measured the neural correlates of explicit motor imagery of gait during observation of in-motion videos shot in a park with a steady cam (Virtual Walking task). In a 2 × 2 factorial design, we assessed the modulatory effect of gait observation and of foot movement execution on the neural correlates of the Virtual Walking task: in half of the trials, the participants were asked to mentally imitate a human model shown while walking along the same route (mental imitation condition); moreover, for half of all the trials, the participants also performed rhythmic ankle dorsiflexion as a proxy for stepping movements. We found that, beyond the areas associated with the execution of lower limb movements (the paracentral lobule, the supplementary motor area, and the cerebellum), gait imagery also recruited dorsal premotor and posterior parietal areas known to contribute to the adaptation of walking patterns to environmental cues. When compared with mental imitation, motor imagery recruited a more extensive network, including a brainstem area compatible with the human mesencephalic locomotor region (MLR). Reduced activation of the MLR in mental imitation indicates that this more visually guided task poses less demand on subcortical structures crucial for internally generated gait patterns. This finding may explain why patients with subcortical degeneration benefit from rehabilitation protocols based on gait observation. Hum Brain Mapp 38:5195-5216, 2017. © 2017 Wiley Periodicals, Inc.

Mental workload and neural efficiency quantified in the prefrontal cortex using fNIRS

An improved understanding of how the brain allocates mental resources as a function of task difficulty is critical for enhancing human performance. Functional near infrared spectroscopy (fNIRS) is a field-deployable optical brain monitoring technology that provides a direct measure of cerebral blood flow in response to cognitive activity. We found that fNIRS was sensitive to variations in task difficulty in both real-life (flight simulator) and laboratory settings (tests measuring executive functions), showing increased concentration of oxygenated hemoglobin (HbO2) and decreased concentration of deoxygenated hemoglobin (HHb) in the prefrontal cortex as the tasks became more complex. Intensity of prefrontal activation (HbO2 concentration) was not clearly correlated to task performance. Rather, activation intensity shed insight on the level of mental effort, i.e., how hard an individual was working to accomplish a task. When combined with performance, fNIRS provided an estimate of the participants' neural efficiency, and this efficiency was consistent across levels of difficulty of the same task. Overall, our data support the suitability of fNIRS to assess the mental effort related to human operations and represents a promising tool for the measurement of neural efficiency in other contexts such as training programs or the clinical setting.

Site Specificity of Changes in Cortical Oxyhaemoglobin Concentration Induced by Water Immersion

Our previous studies have shown that water immersion (WI) changes sensorimotor processing and cortical excitability in the sensorimotor regions of the brain. The present study examined the site specificity of the brain activation during WI using functional near infrared spectroscopy (fNIRS). Cortical oxyhaemoglobin (O₂Hb) levels in the anterior and posterior parts of the supplementary motor area (pre-SMA and SMA), primary motor cortex (M1), primary somatosensory cortex (S1), and posterior parietal cortex (PPC) were recorded using fNIRS (OMM-3000; Shimadzu Co.) before, during, and after WI in nine healthy participants. The cortical O₂Hb levels in SMA, M1, S1, and PPC significantly increased during the WI and increased gradually along with the filling of the WI tank. These changes were not seen in the pre-SMA. The results show that WI-induced increases in cortical O₂Hb levels are at least somewhat site specific: there was little brain activation in response to somatosensory input in the pre-SMA, but robust activation in other areas.

Frontal brain activation changes due to dual-tasking under partial body weight support conditions in older adults with multiple sclerosis

Background

Gait impairments present while dual-tasking in older adults with multiple sclerosis (MS) have been associated with an increased risk of falls. Prior studies have examined prefrontal cortex (PFC) activity using functional near infrared spectroscopy (fNIRS) while dual-tasking in older adults with and without cognitive impairment. While the benefits of partial body weight support (PBWS) on gait have been clearly outlined in the literature, the potential use of PBWS to improve the ability to dual task in older adults with and without MS has not been examined. The aim of this study was to examine the effects of PBWS on the PFC activation while dual-tasking in older adults with and without MS.

Methods

Ten individuals with MS (mean 56.2 ± 5.1 yrs., 8 females) and 12 healthy older adults (HOA) (mean 63.1 ± 4.4 yrs., 9 females) participated in this study. PFC activation (i.e., oxygenated hemoglobin-HbO₂) was measured using fNIRS. Assessments were done under two treadmill walking conditions: no body weight support (NBWS) and PBWS. Under each condition, participants were asked to walk at a comfortable speed (W) or walk and talk (WT). Linear mixed models were used to test for differences between cohorts, conditions, and tasks.

Results

HbO₂ levels differed significantly between task (p < .001), cohort (p < .001), and BWS (p = .02). HbO₂ levels increased under higher cognitive demands (i.e., W vs WT), in individuals with MS, and under different conditions (i.e., NBWS vs PBWS). Post-hoc analysis demonstrated a significant difference between cohorts during the WT and NBWS condition (p = .05). When examining the relative change in HbO₂ levels during each task, a significant interaction between task, BWS, and cohort across time was observed (p < 0.01). While HOA increased PFC activation across time, MS exhibited a maintenance of PFC activation patterns during the WT under PBWS condition.

Conclusions

This study establishes the potential impact of PBWS on PFC activation patterns under dual-tasking conditions and sheds light on the ability for PBWS to be used as a therapeutic tool in individuals with neurological conditions to decrease cognitive demands while dual-tasking and thus decrease the risk of falls.

Motor learning in a complex balance task and associated neuroplasticity: a comparison between endurance athletes and nonathletes

Studies suggested that motor expertise is associated with functional and structural brain alterations, which positively affect sensorimotor performance and learning capabilities. The purpose of the present study was to unravel differences in motor skill learning and associated functional neuroplasticity between endurance athletes (EA) and nonathletes (NA). For this purpose, participants had to perform a multimodal balance task (MBT) training on 2 sessions, which were separated by 1 wk. Before and after MBT training, a static balance task (SBT) had to be performed. MBT-induced functional neuroplasticity and neuromuscular alterations were assessed by means of functional near-infrared spectroscopy (fNIRS) and electromyography (EMG) during SBT performance. We hypothesized that EA would showed superior initial SBT performance and stronger MBT-induced improvements in SBT learning rates compared with NA. On a cortical level, we hypothesized that MBT training would lead to differential learning-dependent functional changes in motor-related brain regions [such as primary motor cortex (M1)] during SBT performance. In fact, EA showed superior initial SBT performance, whereas learning rates did not differ between groups. On a cortical level, fNIRS recordings (time × group interaction) revealed a stronger MBT-induced decrease in left M1 and inferior parietal lobe (IPL) for deoxygenated hemoglobin in EA. Even more interesting, learning rates were correlated with fNIRS changes in right M1/IPL. On the basis of these findings, we provide novel evidence for superior MBT training-induced functional neuroplasticity in highly trained athletes. Future studies should investigate these effects in different sports disciplines to strengthen previous work on experience-dependent neuroplasticity.NEW & NOTEWORTHY Motor expertise is associated with functional/structural brain plasticity. How such neuroplastic reorganization translates into altered motor learning processes remains elusive. We investigated endurance athletes (EA) and nonathletes (NA) in a multimodal balance task (MBT). EA showed superior static balance performance (SBT), whereas MBT-induced SBT improvements did not differ between groups. Functional near-infrared spectroscopy recordings revealed a differential MBT training-induced decrease of deoxygenated hemoglobin in left primary motor cortex and inferior parietal lobe between groups.

Effects of exercise on brain activity during walking in older adults: a randomized controlled trial

BACKGROUND

Physical activity may preserve neuronal plasticity, increase synapse formation, and cause the release of hormonal factors that promote neurogenesis and neuronal function. Previous studies have reported enhanced neurocognitive function following exercise training. However, the specific cortical regions activated during exercise training remain largely undefined. In this study, we quantitatively and objectively evaluated the effects of exercise on brain activity during walking in healthy older adults.

METHODS

A total of 24 elderly women (75-83 years old) were randomly allocated to either an intervention group or a control group. Those in the intervention group attended 3 months of biweekly 90-min sessions focused on aerobic exercise, strength training, and physical therapy. We monitored changes in regional cerebral glucose metabolism during walking in both groups using positron emission tomography (PET) and [¹⁸F]fluorodeoxyglucose (FDG).

RESULTS

All subjects completed the 3-month experiment and the adherence to the exercise program was 100%. Compared with the control group, the intervention group showed a significantly greater step length in the right foot after 3 months of physical activity. The FDG-PET assessment revealed a significant post-intervention increase in regional glucose metabolism in the left posterior entorhinal cortex, left superior temporal gyrus, and right superior temporopolar area in the intervention group. Interestingly, the control group showed a relative increase in regional glucose metabolism in the left premotor and supplemental motor areas, left and right somatosensory association cortex, and right primary visual cortex after the 3-month period. We found no significant differences in FDG uptake between the intervention and control groups before vs. after the intervention.

CONCLUSION

Exercise training increased activity in specific brain regions, such as the precuneus and entorhinal cortices, which play an important role in episodic and spatial memory. Further investigation is required to confirm whether alterations in glucose metabolism within these regions during walking directly promote physical and cognitive performance.

TRIAL REGISTRATION

UMIN-CTR ( UMIN000021829 ). Retrospectively registered 10 April 2016.

Hemodynamic Response Alterations in Sensorimotor Areas as a Function of Barbell Load Levels during Squatting: An fNIRS Study

Functional near-infrared spectroscopy (fNIRS) serves as a promising tool to examine hemodynamic response alterations in a sports-scientific context. The present study aimed to investigate how brain activity within the human motor system changes its processing in dependency of different barbell load conditions while executing a barbell squat (BS). Additionally, we used different fNIRS probe configurations to identify and subsequently eliminate potential exercise induced systemic confounders such as increases in extracerebral blood flow. Ten healthy, male participants were enrolled in a crossover design. Participants performed a BS task with random barbell load levels (0% 1RM (1 repetition maximum), 20% 1RM and 40% 1RM for a BS) during fNIRS recordings. Initially, we observed global hemodynamic response alterations within and outside the human motor system. However, short distance channel regression of fNIRS data revealed a focalized hemodynamic response alteration within bilateral superior parietal lobe (SPL) for oxygenated hemoglobin (HbO₂) and not for deoxygenated hemoglobin (HHb) when comparing different load levels. These findings indicate that the previously observed load/force-brain relationship for simple and isolated movements is also present in complex multi-joint movements such as the BS. Altogether, our results show the feasibility of fNIRS to investigate brain processing in a sports-related context. We suggest for future studies to incorporate short distance channel regression of fNIRS data to reduce the likelihood of false-positive hemodynamic response alterations during complex whole movements.

The Optimal Speed for Cortical Activation of Passive Wrist Movements Performed by a Rehabilitation Robot: A Functional NIRS Study

Objectives: To advance development of rehabilitation robots, the conditions to induce appropriate brain activation during rehabilitation performed by robots should be optimized, based on the concept of brain plasticity. In this study, we examined differences in cortical activation according to the speed of passive wrist movements performed by a rehabilitation robot. Methods: Twenty three normal subjects participated in this study. Passive movements of the right wrist were performed by the wrist rehabilitation robot at three different speeds: 0.25 Hz; slow, 0.5 Hz; moderate and 0.75 Hz; fast. We used functional near-infrared spectroscopy to measure the brain activity accompanying the passive movements performed by a robot. The relative changes in oxy-hemoglobin (HbO) were measured in two regions of interest (ROI): the primary sensory-motor cortex (SM1) and premotor area (PMA). Results: In the left SM1 the HbO value was significantly higher at 0.5 Hz, compared with movements performed at 0.25 Hz and 0.75 Hz (p < 0.05), while no significant differences were observed in the left PMA (p > 0.05). In the group analysis, the left SM1 was activated during passive movements at three speeds (uncorrected p < 0.05) and the greatest activation in the SM1 was observed at 0.5 Hz. Conclusions: In conclusion, the contralateral SM1 showed the greatest activation by a moderate speed (0.5 Hz) rather than slow (0.25 Hz) and fast (0.75 Hz) speed. Our results suggest an ideal speed for execution of the wrist rehabilitation robot. Therefore, our results might provide useful data for more effective and empirically-based robot rehabilitation therapy.

Influence of functional task-oriented mental practice on the gait of transtibial amputees: a randomized, clinical trial

Background

Mental practice (MP) through motor imagery is a cognitive training strategy used to improve locomotor skills during rehabilitation programs. Recent works have used MP tasks to investigate the neurophysiology of human gait; however, its effect on functional performance has not been evaluated. In the present study, the influence of gait-oriented MP tasks on the rehabilitation process of gait in transtibial amputees was investigated by assessing the vertical (V), anterior-posterior (AP), and medio-lateral (ML) ground reaction forces (GRFs) and the time duration of the support phase of the prosthetic limb.

Methods

Unilateral transtibial amputees, who were capable of performing motor imagination tasks (MIQ-RS score ≥4), were randomly divided into two groups: Group A (n = 10), who performed functional gait-oriented MP combined with gait training, and Group B (n = 5), who performed non-motor task MP. The MP intervention was performed in the first-person perspective for 40 min, 3 times/week, for 4 weeks. The GRF outcome measures were recorded by a force platform to evaluate gait performance during 4 distinct stages: at baseline (BL), 1 month before the MP session; Pre-MP, 1–3 days before the MP session; Post-MP, 1–3 days after the MP session; and follow-up (FU), 1 month after MP session. The gait variables were compared inter- and intra-group by applying the Mann-Whitney and Friedman tests (alpha = 0.05).

Results

All volunteers exhibited a homogenous gait pattern prior to MP intervention, with no gait improvement during the BL and Pre-MP stages. Only Group A showed significant improvements in gait performance after the intervention, with enhanced impact absorption, as indicated by decreased first V and AP peaks; propulsion capacity, indicated by increasing second V and AP peaks; and balance control of the prosthetic limb, indicated by decreasing ML peaks and increasing duration of support. This gait pattern persisted until the FU stage.

Conclusions

MP combined with gait training allowed transtibial amputees to reestablish independent locomotion. Since the effects of MP were preserved after 1 month, the improvement is considered related to the specificity of the MP tasks. Therefore, MP may improve the clinical aspect of gait rehabilitation when included in a training program.

Cognitive Resources Necessary for Motor Control in Older Adults Are Reduced by Walking and Coordination Training

We examined if physical exercise interventions were effective to reduce cognitive brain resources recruited while performing motor control tasks in older adults. Forty-three older adults (63-79 years of age) participated in either a walking (n = 17) or a motor coordination (n = 15) intervention (1 year, 3 times per week) or were assigned to a control group (n = 11) doing relaxation and stretching exercises. Pre and post the intervention period, we applied functional MRI to assess brain activation during imagery of forward and backward walking and during counting backwards from 100 as control task. In both experimental groups, activation in the right dorsolateral prefrontal cortex (DLPFC) during imagery of forward walking decreased from pre- to post-test (Effect size: -1.55 and -1.16 for coordination and walking training, respectively; Cohen's d). Regression analysis revealed a significant positive association between initial motor status and activation change in the right DLPFC (R2 = 0.243, F(3,39) = 4.18, p = 0.012). Participants with lowest motor status at pretest profited most from the interventions. Data suggest that physical training in older adults is effective to free up cognitive resources otherwise needed for the control of locomotion. Training benefits may become particularly apparent in so-called dual-task situations where subjects must perform motor and cognitive tasks concurrently.

Neuroimaging of Human Balance Control: A Systematic Review

This review examined 83 articles using neuroimaging modalities to investigate the neural correlates underlying static and dynamic human balance control, with aims to support future mobile neuroimaging research in the balance control domain. Furthermore, this review analyzed the mobility of the neuroimaging hardware and research paradigms as well as the analytical methodology to identify and remove movement artifact in the acquired brain signal. We found that the majority of static balance control tasks utilized mechanical perturbations to invoke feet-in-place responses (27 out of 38 studies), while cognitive dual-task conditions were commonly used to challenge balance in dynamic balance control tasks (20 out of 32 studies). While frequency analysis and event related potential characteristics supported enhanced brain activation during static balance control, that in dynamic balance control studies was supported by spatial and frequency analysis. Twenty-three of the 50 studies utilizing EEG utilized independent component analysis to remove movement artifacts from the acquired brain signals. Lastly, only eight studies used truly mobile neuroimaging hardware systems. This review provides evidence to support an increase in brain activation in balance control tasks, regardless of mechanical, cognitive, or sensory challenges. Furthermore, the current body of literature demonstrates the use of advanced signal processing methodologies to analyze brain activity during movement. However, the static nature of neuroimaging hardware and conventional balance control paradigms prevent full mobility and limit our knowledge of neural mechanisms underlying balance control.

Dynamic Increase in Corticomuscular Coherence during Bilateral, Cyclical Ankle Movements

In humans, the midline primary motor cortex is active during walking. However, the exact role of such cortical participation is unknown. To delineate the role of the primary motor cortex in walking, we examined whether the primary motor cortex would activate leg muscles during movements that retained specific requirements of walking (i.e., locomotive actions). We recorded electroencephalographic and electromyographic signals from 15 healthy, young men while they sat and performed bilateral, cyclical ankle movements. During dorsiflexion, near-20-Hz coherence increased cyclically between the midline primary motor cortex and the co-contracting antagonistic pair (i.e., tibialis anterior and medial gastrocnemius muscles) in both legs. Thus, we have shown that dynamic increase in corticomuscular coherence, which has been observed during walking, also occurs during simple bilateral cyclical movements of the feet. A possible mechanism for such coherence is corticomuscular communication, in which the primary motor cortex participates in the control of movement. Furthermore, because our experimental task isolated certain locomotive actions, the observed coherence suggests that the human primary motor cortex may participate in these actions (i.e., maintaining a specified movement frequency, bilaterally coordinating the feet, and stabilizing the posture of the feet). Additional studies are needed to identify the exact cortical and subcortical interactions that cause corticomuscular coherence and to further delineate the functional role of the primary motor cortex during bilateral cyclical movements such as walking.

Dynamic cortical participation during bilateral, cyclical ankle movements: effects of aging

The precise role of the human primary motor cortex in walking is unknown. Our previous study showed that the primary motor cortex may contribute to specific requirements of walking (i.e., maintaining a constant movement frequency and bilaterally coordinating the feet). Because aging can impair (i) the ability to fulfill the aforementioned requirements and (ii) corticomuscular communication, we hypothesized that aging would impair the motoneuronal recruitment by the primary motor cortex during bilateral cyclical movements. Here, we used corticomuscular coherence (i.e., coherence between the primary motor cortex and the active muscles) to examine whether corticomuscular communication is affected in older individuals during cyclical movements that shared some functional requirements with walking. Fifteen young men and 9 older men performed cyclical, anti-phasic dorsiflexion and plantarflexion of the feet while seated. Coherence between the midline primary motor cortex and contracting leg muscles cyclically increased in both age groups. However, the coherence of older participants was characterized by (i) lower magnitude and (ii) mediolaterally broader and more rostrally centered cortical distributions. These characteristics suggest that aging changes how the primary motor cortex participates in the cyclical movements, and such change may extend to walking.

The neural substrate of gait and executive function relationship in elderly women: A PET study

AIM

Understanding the relationship between age-related gait impairment, such as slow gait, and executive functioning in seniors may help identify individuals at higher risk of mobility decline, falls, and progression to dementia at earlier stages. We aim to identify brain regions concomitantly associated with poor gait and executive functioning in a cohort of well-functioning elderly women.

METHODS

In total, 149 well-functioning women aged 70.1 ± 6.2 years underwent FDG-PET to evaluate regional cerebral metabolic rates of glucose normalized in reference to cerebellar glucose metabolic value (normalized-rCMRglc) in 16 brain areas. We assessed gait speed, step length and cadence under usual and fast conditions. Executive function was assessed using Trail-Making-Tests (TMT) A and B.

RESULTS

Adjusted multiple regression analyses for potential covariates showed that TMT-B and ΔTMT (TMT B-A) were associated with gait speed and cadence at fast condition. Lower normalized-rCMRglc in the posterior cingulate and primary sensorimotor cortices were associated with longer TMT-B and ΔTMT times (i.e., lower executive function) as well as with slower gait speed and lower cadence at fast condition. Slower gait speed and lower cadence at fast condition were also associated with lower normalized-rCMRglc in the occipital and parietal cortices. There were no other significant associations.

CONCLUSIONS

In healthy elderly women without impending disability or cognitive impairment, reduced glucose metabolism in the posterior cingulate and primary sensorimotor cortices were associated with both lower gait performance and executive functioning. Our results suggest that gait control and executive functions might share the same neural substrate. Geriatr Gerontol Int 2017; 17: 1873-1880.

Stress and gender effects on prefrontal cortex oxygenation levels assessed during single and dual-task walking conditions

The ability to walk is critical for functional independence and wellbeing. The pre-frontal cortex (PFC) plays a key role in cognitive control of locomotion, notably under attention-demanding conditions. Factors that influence brain responses to cognitive demands of locomotion, however, are poorly understood. Herein, we evaluated the individual and combined effects of gender and perceived stress on stride velocity and PFC Oxygenated Hemoglobin (HbO₂ ) assessed during single and dual-task walking conditions. The experimental paradigm included Normal Walk (NW); Cognitive Interference (Alpha); and Walk-While-Talk (WWT) tasks. An instrumented walkway was used to assess stride velocity in NW and WWT conditions. Functional Near-Infrared-Spectroscopy (fNIRS) was used to quantify PFC HbO₂ levels during NW, Alpha and WWT. Perceived task-related stress was evaluated with a single 11-point scale item. Participants were community residing older adults (age = 76.8 ± 6.7 years; %female = 56). Results revealed that higher perceived stress was associated with greater decline in stride velocity from single to dual-task conditions among men. Three-way interactions revealed that gender moderated the effect of perceived stress on changes in HbO₂ levels comparing WWT to NW and Alpha. Attenuation in the increase in HbO₂ levels, in high compared to low perceived stress levels, from the two single task conditions to WWT was observed only in men. Thus, older men may be more vulnerable to the effect of perceived stress on the change in PFC oxygenation levels across walking conditions that vary in terms of cognitive demands. These findings confer important implications for assessment and treatment of individuals at risk of mobility impairments.

The cortical activation pattern during bilateral arm raising movements

Bilateral arm raising movements have been used in brain rehabilitation for a long time. However, no study has been reported on the effect of these movements on the cerebral cortex. In this study, using functional near infrared spectroscopy (fNIRS), we attempted to investigate cortical activation generated during bilateral arm raising movements. Ten normal subjects were recruited for this study. fNIRS was performed using an fNIRS system with 49 channels. Bilateral arm raising movements were performed in sitting position at the rate of 0.5 Hz. We measured values of oxyhemoglobin and total hemoglobin in five regions of interest: the primary sensorimotor cortex, premotor cortex, supplementary motor area, prefrontal cortex, and posterior parietal cortex. During performance of bilateral arm raising movements, oxyhemoglobin and total hemoglobin values in the primary sensorimotor cortex, premotor cortex, supplementary motor area, and prefrontal cortex were similar, but higher in these regions than those in the prefrontal cortex. We observed activation of the arm somatotopic areas of the primary sensorimotor cortex and premotor cortex in both hemispheres during bilateral arm raising movements. According to this result, bilateral arm raising movements appeared to induce large-scale neuronal activation and therefore arm raising movements would be good exercise for recovery of brain functions.

Passive cycling in neurorehabilitation after spinal cord injury: A review

CONTEXT/OBJECTIVE

Passive cycling (PC) may represent a potential alternative neurorehabilitation program for patients who are too weak or medically unstable to repeatedly practice active movements. We review here the most important animal and human studies addressing PC after spinal cord injury (SCI).

METHODS

A MEDLINE search was performed using following terms: "passive", "cycling", "pedaling", "pedalling","spinal cord injury".

RESULTS

Experimental studies revealed that PC modulated spinal reflex and reduced spasticity. PC also reduced autonomic dysreflexia and elicited cardio-protective effects. Increased levels of mRNA for brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor and neurotrophin-4 were found. In contrast, human studies failed to show an effect of PC on spasticity reduction and did not support its application for prevention of cardiovascular disease-related secondary complications.

CONCLUSION

Available evidence to support the use of PC as standard treatment in patients with SCI is still rather limited. Since it is conceivable that PC motion could elicit sensory inputs to activate cortical structures and induce cortical plasticity changes leading to improved lower limb motor performance, further carefully designed prospective studies in subjects with SCI are needed.

Different mechanosensory stimulations of the lower back elicit specific changes in hemodynamics and oxygenation in cortical sensorimotor areas-A fNIRS study

BACKGROUND AND OBJECTIVES

This study aimed at investigating the feasibility of functional near-infrared spectroscopy (fNIRS) to measure changes in cerebral hemodynamics and oxygenation evoked by painful and nonpainful mechanosensory stimulation on the lower back. The main objectives were to investigate whether cortical activity can be (1) detected using functional fNIRS, and (2) if it is possible to distinguish between painful and nonpainful pressure as well as a tactile brushing stimulus based on relative changes in oxy- and deoxyhemoglobin ([O2Hb] and [HHb]).

METHODS

Twenty right-handed subjects (33.5 ± 10.7 years; range 20-61 years; 8 women) participated in the study. Painful and nonpainful pressure stimulation was exerted with a thumb grip perpendicularly to the spinous process of the lumbar spine. Tactile stimulation was realized by a one-finger brushing. The supplementary motor area (SMA) and primary somatosensory cortex (S1) were measured bilaterally using a multichannel continuous-wave fNIRS imaging system.

RESULTS

Characteristic relative changes in [O2Hb] in the SMA and S1 after both pressure stimulations (corrected for multiple comparison) were observed. [HHb] showed only much weaker changes (uncorrected). The brushing stimulus did not reveal any significant changes in [O2Hb] or [HHb].

CONCLUSION

The results indicate that fNIRS is sensitive enough to detect varying hemodynamic responses to different types of mechanosensory stimulation. The acquired data will serve as a foundation for further investigations in patients with chronic lower back pain. The future aim is to disentangle possible maladaptive neuroplastic changes in sensorimotor areas during painful and nonpainful lower back stimulations based on fNIRS neuroimaging.

Functional brain imaging of walking while talking - An fNIRS study

Since functional imaging of whole body movements is not feasible with functional magnetic resonance imaging (fMRI), the present study presents in vivo functional near-infrared spectroscopy (fNIRS) as a suitable technique to measure body movement effects on fronto-temporo-parietal cortical activation in single- and dual-task paradigms. Previous fNIRS applications in studies addressing whole body movements were typically limited to the assessment of prefrontal brain areas. The current study investigated brain activation in the frontal, temporal and parietal cortex of both hemispheres using functional near-infrared spectroscopy (fNIRS) with two large 4×4 probe-sets with 24 channels each during single and dual gait tasks. 12 young healthy adults were measured using fNIRS walking on a treadmill: the participants performed two single-task (ST) paradigms (walking at different speeds, i.e. 3 and 5km/h) and a dual task (DT) paradigm where a verbal fluency task (VFT) had to be executed while walking at 3km/h. The results show an increase of activation in Broca's area during the more advanced conditions (ST 5km/h vs. ST 3km/h, DT vs. ST 3km/h, DT vs. 5km/h), while the corresponding area on the right hemisphere was also activated. DT paradigms including a cognitive task in conjunction with whole body movements elicit wide-spread cortical activation patterns across fronto-temporo-parietal areas. An elaborate assessment of these activation patterns requires more extensive fNIRS assessments than the traditional prefrontal investigations, e.g. as performed with portable fNIRS devices.

Best facilitated cortical activation during different stepping, treadmill, and robot-assisted walking training paradigms and speeds: A functional near-infrared spectroscopy neuroimaging study

BACKGROUND

Robot-assisted and treadmill-gait training are promising neurorehabilitation techniques, with advantages over conventional gait training, but the neural substrates underpinning locomotor control remain unknown particularly during different gait training modes and speeds.

OBJECTIVE

The present optical imaging study compared cortical activities during conventional stepping walking (SW), treadmill walking (TW), and robot-assisted walking (RW) at different speeds.

METHODS

Fourteen healthy subjects (6 women, mean age 30.06, years ± 4.53) completed three walking training modes (SW, TW, and RW) at various speeds (self-selected, 1.5, 2.0, 2.5, and 3.0  km/h). A functional near-infrared spectroscopy (fNIRS) system determined cerebral hemodynamic changes associated with cortical locomotor network areas in the primary sensorimotor cortex (SMC), premotor cortex (PMC), supplementary motor area (SMA), prefrontal cortex (PFC), and sensory association cortex (SAC).

RESULTS

There was increased cortical activation in the SMC, PMC, and SMA during different walking training modes. More global locomotor network activation was observed during RW than TW or SW. As walking speed increased, multiple locomotor network activations were observed, and increased activation power spectrum.

CONCLUSIONS

This is the first empirical evidence highlighting the neural substrates mediating dynamic locomotion for different gait training modes and speeds. Fast, robot-assisted gait training best facilitated cortical activation associated with locomotor control.

Comparable Cerebral Oxygenation Patterns in Younger and Older Adults during Dual-Task Walking with Increasing Load

The neuroimaging literature on dual-task gait clearly demonstrates increased prefrontal cortex (PFC) involvement when performing a cognitive task while walking. However, findings from direct comparisons of the cerebral oxygenation patterns of younger (YA) and older (OA) adults during dual-task walking are mixed and it is unclear how YA and OA respond to increasing cognitive load (difficulty) while walking. This functional near infra-red (fNIRS) study examined cerebral oxygenation of YA and OA during self-paced dual-task treadmill walking at two different levels of cognitive load (auditory n-back). Changes in accuracy (%) as well as oxygenated (HbO) and deoxygenated (HbR) hemoglobin were examined. For the HbO and HbR measures, eight regions of interest (ROIs) were assessed: the anterior and posterior dorsolateral and ventrolateral PFC (aDLPFC, pDLPFC, aVLPFC, pVLPFC) in each hemisphere. Nineteen YA (M = 21.83 years) and 14 OA (M = 66.85 years) walked at a self-selected pace while performing auditory 1-back and 2-back tasks. Walking alone (single motor: SM) and performing the cognitive tasks alone (single cognitive: SC) were compared to dual-task walking (DT = SM + SC). In the behavioural data, participants were more accurate in the lowest level of load (1-back) compared to the highest (2-back; p < 0.001). YA were more accurate than OA overall (p = 0.009), and particularly in the 2-back task (p = 0.048). In the fNIRS data, both younger and older adults had task effects (SM < DT) in specific ROIs for ΔHbO (three YA, one OA) and ΔHbR (seven YA, eight OA). After controlling for walk speed differences, direct comparisons between YA and OA did not reveal significant age differences, but did reveal a difficulty effect in HbO in the left aDLPFC (p = 0.028) and significant task effects (SM < DT) in HbR for six of the eight ROIs. Findings suggest that YA and OA respond similarly to manipulations of cognitive load when walking on a treadmill at a self-selected pace.

Quantitative Assessment of Head Motion toward Functional Magnetic Resonance Imaging during Stepping

Purpose:

Stepping motions have been often used as gait-like patterns in functional magnetic resonance imaging (fMRI) to understand gait control. However, it is still very difficult to stabilize the task-related head motion. Our main purpose is to provide characteristics of the task-related head motion during stepping to develop robust restraints toward fMRI.

Methods:

Multidirectional head and knee position during stepping were acquired using a motion capture system outside MRI room in 13 healthy participants. Six phases in a stepping motion were defined by reference to the left knee angles and the mean of superior-inferior head velocity (V_mean) in each phase was investigated. Furthermore, the correlation between the standard deviation of the knee angle (θ_sd) and the maximum of the head velocity (V_max) was evaluated.

Results:

The standard deviation of each superior-inferior head position and pitch were significantly larger than the other measurements. V_mean showed a characteristic repeating pattern associated with the knee angle. Additionally, there were significant correlations between θ_sd and V_max.

Conclusions:

This is the first report to reveal the characteristics of the task-related head motion during stepping. Our findings are an essential step in the development of robust restraint toward fMRI during stepping task.

Review of functional near-infrared spectroscopy in neurorehabilitation

We provide a brief overview of the research and clinical applications of near-infrared spectroscopy (NIRS) in the neurorehabilitation field. NIRS has several potential advantages and shortcomings as a neuroimaging tool and is suitable for research application in the rehabilitation field. As one of the main applications of NIRS, we discuss its application as a monitoring tool, including investigating the neural mechanism of functional recovery after brain damage and investigating the neural mechanisms for controlling bipedal locomotion and postural balance in humans. In addition to being a monitoring tool, advances in signal processing techniques allow us to use NIRS as a therapeutic tool in this field. With a brief summary of recent studies investigating the clinical application of NIRS using motor imagery task, we discuss the possible clinical usage of NIRS in brain-computer interface and neurofeedback.

Correction of motion artifacts and serial correlations for real-time functional near-infrared spectroscopy

Functional near-infrared spectroscopy (fNIRS) is a relatively low-cost, portable, noninvasive neuroimaging technique for measuring task-evoked hemodynamic changes in the brain. Because fNIRS can be applied to a wide range of populations, such as children or infants, and under a variety of study conditions, including those involving physical movement, gait, or balance, fNIRS data are often confounded by motion artifacts. Furthermore, the high sampling rate of fNIRS leads to high temporal autocorrelation due to systemic physiology. These two factors can reduce the sensitivity and specificity of detecting hemodynamic changes. In a previous work, we showed that these factors could be mitigated by autoregressive-based prewhitening followed by the application of an iterative reweighted least squares algorithm offline. This current work extends these same ideas to real-time analysis of brain signals by modifying the linear Kalman filter, resulting in an algorithm for online estimation that is robust to systemic physiology and motion artifacts. We evaluated the performance of the proposed method via simulations of evoked hemodynamics that were added to experimental resting-state data, which provided realistic fNIRS noise. Last, we applied the method post hoc to data from a standing balance task. Overall, the new method showed good agreement with the analogous offline algorithm, in which both methods outperformed ordinary least squares methods.

Hemodynamic Response of the Supplementary Motor Area during Locomotor Tasks with Upright versus Horizontal Postures in Humans

To understand cortical mechanisms related to truncal posture control during human locomotion, we investigated hemodynamic responses in the supplementary motor area (SMA) with quadrupedal and bipedal gaits using functional near-infrared spectroscopy in 10 healthy adults. The subjects performed three locomotor tasks where the degree of postural instability varied biomechanically, namely, hand-knee quadrupedal crawling (HKQuad task), upright quadrupedalism using bilateral Lofstrand crutches (UpQuad task), and typical upright bipedalism (UpBi task), on a treadmill. We measured the concentration of oxygenated hemoglobin (oxy-Hb) during the tasks. The oxy-Hb significantly decreased in the SMA during the HKQuad task, whereas it increased during the UpQuad task. No significant responses were observed during the UpBi task. Based on the degree of oxy-Hb responses, we ranked these locomotor tasks as UpQuad > UpBi > HKQuad. The order of the different tasks did not correspond with postural instability of the tasks. However, qualitative inspection of oxy-Hb time courses showed that oxy-Hb waveform patterns differed between upright posture tasks (peak-plateau-trough pattern for the UpQuad and UpBi tasks) and horizontal posture task (downhill pattern for the HKQuad task). Thus, the SMA may contribute to the control of truncal posture accompanying locomotor movements in humans.

Using Actual and Imagined Walking Related Desynchronization Features in a BCI

Recently, brain-computer interface (BCI) research has extended to investigate its possible use in motor rehabilitation. Most of these investigations have focused on the upper body. Only few studies consider gait because of the difficulty of recording EEG during gross movements. However, for stroke patients the rehabilitation of gait is of crucial importance. Therefore, this study investigates if a BCI can be based on walking related desynchronization features. Furthermore, the influence of complexity of the walking movements on the classification performance is investigated. Two BCI experiments were conducted in which healthy subjects performed a cued walking task, a more complex walking task (backward or adaptive walking), and imagination of the same tasks. EEG data during these tasks was classified into walking and no-walking. The results from both experiments show that despite the automaticity of walking and recording difficulties, brain signals related to walking could be classified rapidly and reliably. Classification performance was higher for actual walking movements than for imagined walking movements. There was no significant increase in classification performance for both the backward and adaptive walking tasks compared with the cued walking tasks. These results are promising for developing a BCI for the rehabilitation of gait.

Electroencephalographic Motor Imagery Brain Connectivity Analysis for BCI: A Review

Recent research has reached a consensus on the feasibility of motor imagery brain-computer interface (MI-BCI) for different applications, especially in stroke rehabilitation. Most MI-BCI systems rely on temporal, spectral, and spatial features of single channels to distinguish different MI patterns. However, no successful communication has been established for a completely locked-in subject. To provide more useful and informative features, it has been recommended to take into account the relationships among electroencephalographic (EEG) sensor/source signals in the form of brain connectivity as an efficient tool of neuroscience. In this review, we briefly report the challenges and limitations of conventional MI-BCIs. Brain connectivity analysis, particularly functional and effective, has been described as one of the most promising approaches for improving MI-BCI performance. An extensive literature on EEG-based MI brain connectivity analysis of healthy subjects is reviewed. We subsequently discuss the brain connectomes during left and right hand, feet, and tongue MI movements. Moreover, key components involved in brain connectivity analysis that considerably affect the results are explained. Finally, possible technical shortcomings that may have influenced the results in previous research are addressed and suggestions are provided.