Altered cortical activation during a motor task in ALS

Abstract Objective To test the hypothesis that patients with amyotrophic lateral sclerosis (ALS) show increased cortical activation during a motor task compared to both healthy controls and patients with muscle weakness due to peripheral lesions. Methods Functional magnetic resonance imaging (fMRI) was used to measure activation during a block design paradigm contrasting right hand movements against rest in sixteen patients with ALS, seventeen healthy controls and nine patients with peripheral lesions. The groups were matched for age and gender and the two patient groups were matched for their degree of upper limb weakness. Analysis used a non-parametric approach to perform a 3 way hypothesis-driven comparison between the groups. Results During the motor task, patients with ALS showed increased cortical activation bilaterally, extending from the sensorimotor cortex [Brodmann areas (BA) 1, 2, 4] posteriorly into the inferior parietal lobule (BA 40) and inferiorly to the superior temporal gyrus (BA 22) when compared to peripheral lesion patients and controls. In addition, ALS patients showed reduced activation in the dorsolateral prefrontal cortex (DLPFC) extending to anterior and medial frontal cortex (BA 8, 9, 10, 32). Conclusions We conclude that alterations in cortical function in ALS differ in sensorimotor and prefrontal regions. Importantly, we have shown that these changes do not reflect confounding by weakness or task difficulty, but are likely to be related to upper motor neuron pathology in ALS.     

Non-paretic lower limb muscle wasting during acute phase is associated with dependent ambulation in patients with stroke

BackgroundMuscle wasting in patients with stroke is a factor for a poor functional outcome. However, there have been few studies on the relationships between lower limb muscle wasting during the acute phase and dependent ambulation. This study examined whether lower limb muscle wasting during the acute phase is associated with the dependent ambulation status at 3 months after stroke.MethodsIn this observational cohort study, we measured the quadriceps muscle thickness in the paretic and non-paretic limbs within 1 and 3 weeks after admission using ultrasonography in non-ambulatory patients with acute stroke. Patients were categorized into two groups based on their ambulation ability: dependent, functional ambulation category (FAC) 0–3 and independent, FAC 4–5) at 3 months after stroke.ResultsIn total, 55 patients were included and completed follow-up, and 28 patients (51%) had an ambulation status of dependent at 3 months after stroke. Significant differences in muscle wasting were observed in the non-paretic limb (−5.5% [8.7%] : −16.8% [13.6%], independent group: dependent group, respectively, P < 0.001), but not in the paretic limb (−15.0% [14.3%] : −18.7% [15.1%], P = 0.36). Even after adjusting for covariates, muscle wasting in the non-paretic limb was a significant independent predictor of dependent ambulation (adjusted odds ratio, 0.87; 95% confidence interval, 0.76–0.99, P = 0.033).ConclusionPost-stroke muscle wasting in the non-paretic lower limb during the acute phase is independently associated with dependent ambulation after stroke.     

Longitudinal Relationship Between Intramuscular Fat in the Quadriceps and Gait Independence in Convalescent Stroke Patients

Background and AimIn a cross-sectional study, intramuscular fat in the quadriceps of stroke patients has been associated with gait independence. However, the longitudinal relationship between intramuscular fat and gait independence remain unclear. If these relationships are clarified, it can be demonstrated that improvement in gait independence eventually contributes to improved intramuscular fat in the quadriceps of stroke patients. The aim of this study was to investigate the longitudinal relationship between intramuscular fat in the quadriceps and gait independence in convalescent stroke patients.MethodsEleven stroke patients participated in this study. Gait independence was assessed using the Functional Independence Measure (FIM) gait score. The intramuscular fat in the quadriceps was assessed using ultrasound echo intensity, whereas higher echo intensity indicated greater intramuscular fat. The baseline and discharge assessment values for the echo intensity of the quadriceps were compared using a paired t-test. Correlation analysis of the FIM gait score gain and echo intensity changes in the quadriceps on the paretic and non-paretic sides was performed using Kendall's rank correlation coefficient.ResultsFor quadriceps on the paretic side, echo intensity values at discharge were significantly lower than those at admission. However there was no significant difference for quadriceps on the non-paretic side (paretic side: 19.9% decrease; non-paretic side: 8.0% decrease). We observed that the change in the echo intensity of quadriceps on the non-paretic side was negatively corelated with FIM gait score gain.ConclusionsOur results revealed a strong correlation between longitudinal change in intramuscular fat in the quadriceps and gait independence, implying that improved gait independence in convalescent stroke patients might have a positive effect on improvements in intramuscular fat.     

Non-paretic quadriceps activity influences paretic quadriceps activity post-stroke

Objective

Inappropriate muscle activity is common following stroke. Paretic muscle activation may be influenced by non-paretic volitional activation. We examined the influence of non-paretic quadriceps activation on paretic quadriceps excitability.

Methods

Individuals with chronic stroke performed bilateral and unilateral (paretic and non-paretic) maximum voluntary isometric contractions. Peak torque and muscle activity were compared between conditions. An instrumented tendon tapper elicited a patellar tendon reflex of the relaxed paretic leg while the non-paretic leg was relaxed and pre-activated. The threshold to elicit a paretic quadriceps response was compared between conditions.

Results

During the bilateral MVIC, the paretic quadriceps generated less absolute torque, but greater relative torque than the non-paretic side when normalized to the respective unilateral condition (p < 0.05). During reflex testing, the tendon tapping threshold to elicit paretic muscle and torque responses decreased with non-paretic activity (p < 0.05).

Conclusions

Concurrent non-paretic activation resulted in a relative disinhibition of the paretic quadriceps. The paretic limb’s inability to remain inactive during isolated non-paretic contractions implies increased excitation or decreased inhibition of paretic motor pools, although the source remains unknown.

Significance

Unwanted muscle activity during reciprocal tasks (gait training) may be due to contralateral effects of non-paretic muscle activity.     

Comparing executive function,evoked hemodynamic response,and gait as predictors of variations in mobility for older adults

Objective: Falls represent a major concern for older adults and may serve as clinically salient index events for those presenting in the prodromal stages of mild cognitive impairment. Declines in executive function performance and in gait consistency have shown promise in predicting fall risk; however, associated neurophysiological underpinnings have received less attention. In this study, we used a multimodal approach to assess fall risk in a group of older adults with and without a previous fall history.

Method: Processing speed, inductive reasoning, verbal fluency, crystallized ability, episodic memory, and executive functioning were assessed using standardized neuropsychological tests. Cognitive interference was assessed using the Multi-Source Interference Task. Spatiotemporal gait parameters were assessed with and without cognitive load using a 6.4-m instrumented walkway. Hemodynamic responses were measured using functional near-infrared spectroscopy.

Results: Whereas no group differences were observed in cognitive behavioral performance, during a cognitive interference task fallers displayed more oxygenated hemoglobin across the prefrontal cortex than nonfallers, suggesting that engaging in the cognitive task was more effortful for them overall, therefore eliciting greater cortical activation. Between-group differences in spatial as well as temporal gait parameters were also observed.

Conclusions: These results are in keeping with assertions that diminished executive control is related to fall risk. Notably, the group differences observed in prefrontal cortical activation and in gait parameters may ultimately precede those observed in cognitive behavioral performance, with implications for measurement sensitivity and early identification.     

Peripheral motor nerve conduction abnormality,muscle strength,and muscle wasting in patients with acute stroke: A pilot study

IntroductionStroke-related muscle wasting are important therapeutic targets to reduce disability in patients with stroke. Peripheral nerve conduction impairment is one reported factor that causes muscle wasting in these patients, but muscle strength, muscle wasting, and peripheral nerve conduction abnormality have not been examined in patients with acute stroke. We therefore investigated changes in lower-leg motor nerve conduction, muscle strength, and muscle wasting in patients with acute stroke.MethodsPatients with acute stroke were recruited. Their motor conduction velocity (MCV) and compound motor action potential (CMAP) amplitude in both sides of the common peroneal nerve, and lower paretic leg muscle strength by the Motricity Index (MI) and quadriceps muscle thickness (QMT) on both sides were measured at the time of admission and again 2 weeks later.ResultsEighteen patients with acute stroke (median [interquartile range], age = 68 [14] years; female = 4 [22%]) were enrolled. The MCV and CMAP amplitude were not significantly different between limbs. The QMT was significantly reduced in paretic (P = 0.014) and non-paretic (P = 0.003) limbs, but the lower paretic leg MI was increased (P = 0.0.001). There was a significant correlation between % differences in CMAP amplitude and % differences in QMT in the paretic limb (R = 0.604, P = 0.008), but not in the non-paretic limb (R = 0.225, P = 0.369).ConclusionsLower-leg muscle wasting was associated with the change in CMAP amplitude in paretic limbs, but not in non-paretic limbs, in patients with acute stroke.     

Functional magnetic resonance brain imaging of imagined walking to study locomotor function after stroke

ObjectiveImagined walking has yielded insights into normal locomotor control and could improve understanding of neurologic gait dysfunction. This study evaluated brain activation during imagined walking in chronic stroke.MethodsTen persons with stroke and 10 matched controls completed a walking test battery and a magnetic resonance imaging session including imagined walking and knee extension tasks. Brain activations were compared between tasks and groups. Associations between activations and composite gait score were also calculated, while controlling for lesion load.ResultsStroke and worse gait score were each associated with lesser overall brain activation during knee extension but greater overall activation during imagined walking. During imagined walking, the stroke group significantly activated the primary motor cortex lower limb region and cerebellar locomotor region. Better walking function was associated with less activation of these regions and greater activation of medial superior frontal gyrus area 9.ConclusionsCompared with knee extension, imagined walking was less sensitive to stroke-related deficits in brain activation but better at revealing compensatory changes, some of which could be maladaptive.SignificanceThe identified associations for imagined walking suggest potential neural mechanisms of locomotor adaptation after stroke, which could be useful for future intervention development and prognostication.     

The bilateral movement condition facilitates maximal but not submaximal paretic-limb grip force in people with post-stroke hemiparesis

ObjectivesAlthough healthy individuals have less force production capacity during bilateral muscle contractions compared to unilateral efforts, emerging evidence suggests that certain aspects of paretic upper limb task performance after stroke may be enhanced by moving bilaterally instead of unilaterally. We investigated whether the bilateral movement condition affects grip force differently on the paretic side of people with post-stroke hemiparesis, compared to their non-paretic side and both sides of healthy young adults.MethodsWithin a single session, we compared: (1) maximal grip force during unilateral vs. bilateral contractions on each side, and (2) force contributed by each side during a 30% submaximal bilateral contraction.ResultsHealthy controls produced less grip force in the bilateral condition, regardless of side (?2.4% difference), and similar findings were observed on the non-paretic side of people with hemiparesis (?4.5% difference). On the paretic side, however, maximal grip force was increased by the bilateral condition in most participants (+11.3% difference, on average). During submaximal bilateral contractions in each group, the two sides each contributed the same percentage of unilateral maximal force.ConclusionsThe bilateral condition facilitates paretic limb grip force at maximal, but not submaximal levels.SignificanceIn some people with post-stroke hemiparesis, the paretic limb may benefit from bilateral training with high force requirements.     

Cross-sectional study of quadriceps properties and postural stability in patients with chronic stroke and limited vs. non-limited community ambulation

Background: Changes in the paretic-side metabolism post-stroke and quadriceps muscle mechanical properties favour muscle wasting, affecting postural instability and walking impairment. Further clarification is needed in subjects post-stroke who show limited or non-limited community ambulation.

Objectives: To analyze between-limb differences in quadriceps muscle thickness, strength and thigh cutaneous temperature, as well as investigate postural stability in subjects with chronic stroke and limited vs. non-limited community ambulation and compared against healthy controls.

Methods: In this controlled cross-sectional study, 26 participants with chronic hemiparesis post-stroke (divided in a slow gait group (SG<0.8 m/s) (n = 13) and a fast gait group with full community ambulation speed (FG≥0.8 m/s)) and 18 healthy people were recruited. Thigh surface temperature, rectus femoris (RF) and vastus intermedius (VI) muscles thickness, quadriceps’ isometric maximal voluntary contraction and postural stability were measured.

Results: The SG presented significantly lower RF (P = .019) and VI (P = .006) muscle thickness, less peak force (P < .001) and lower temperature (P = .002) in the paretic vs the non-paretic limb. The FG showed significantly lower VI thickness (P = .036) and peak force (P < .001) in the paretic vs the non-paretic limb. Regarding balance, all indices were worse in the SG versus the FG and CG.

Conclusions: Subjects of the FG, despite showing full community ambulation speed, had less quadriceps strength and VI muscle thickness but not RF muscle wasting in the paretic limb. The paretic VI muscle wasting may be an important factor to reach normal walking. The SG showed between-limb differences in all the studied variables and the worst postural stability.     

Impaired interlimb coordination is related to asymmetries during pedaling after stroke

ObjectiveTo understand whether lower limb asymmetry in chronic stroke is related to paretic motor impairment or impaired interlimb coordination.MethodsStroke and control participants performed conventional, unilateral, and bilateral uncoupled pedaling. During uncoupled pedaling, the pedals were mechanically disconnected. Paretic mechanical work was measured during conventional pedaling. Pedaling velocity and muscle activity were compared across conditions and groups. Relative limb phasing was examined during uncoupled pedaling.ResultsDuring conventional pedaling, EMG and mechanical work were lower in the paretic than the non-paretic limb (asymmetry). During unilateral pedaling with the paretic limb, muscle activity was larger, but velocity was slower and more variable than during conventional pedaling (evidence of paretic motor impairment). During uncoupled pedaling, muscle activity increased further, but velocity was slower and more variable than in other conditions (evidence of impaired interlimb coordination). Relative limb phasing was impaired in stroke participants. Regression analysis suggested that interlimb coordination may be a stronger predictor of asymmetry than paretic motor impairment.ConclusionsParetic motor impairment and impaired interlimb coordination may contribute to asymmetry during pedaling after stroke.SignificanceRehabilitation that addresses paretic motor impairment and impaired interlimb coordination may improve symmetry and maximize improvement.     

Failure of de-activation in the medial frontal cortex in mania: evidence for default mode network dysfunction in the disorder

Abstract

Objectives. Manic patients have been found to show reduced activation in the prefrontal cortex and other regions during performance of cognitive tasks. However, little is known about de-activations associated with the disorder. This study aimed to examine, at the whole-brain level, abnormal patterns of task-related activation and de-activation during performance of a working memory task. Methods. Twenty-nine DSM-IV bipolar patients and 46 healthy controls underwent fMRI during performance of the n-back task. The patients were scanned while they were in a manic episode. Linear models were used to obtain maps of within-group activations and areas of differential activation between the groups. Results. The manic patients showed reduced activation compared to the controls in the bilateral dorsolateral prefrontal cortex and the right parietal cortex. They also showed failure of de-activation in the medial frontal cortex, extending to the temporal poles and parts of the limbic system bilaterally. The failure of activation in the dorsolateral prefrontal cortex disappeared when differences in task performance were controlled for in the analysis. However, the medial frontal failure of de-activation survived controlling for this. Conclusions. This study suggests that, in addition to reduced prefrontal activation, failure of de-activation is an important functional imaging abnormality in mania. This, together with its location in the medial prefrontal cortex, implies default mode network dysfunction in the disorder.     

Prefrontal Cortex Activity and Gait in Parkinson's Disease With Cholinergic and Dopaminergic Therapy

Degradation of striatal dopamine in Parkinson's disease (PD) may initially be supplemented by increased cognitive control mediated by cholinergic mechanisms. Shift to cognitive control of walking can be quantified by prefrontal cortex activation. Levodopa improves certain aspects of gait and worsens others, and cholinergic augmentation influence on gait and prefrontal cortex activity remains unclear. This study examined dopaminergic and cholinergic influence on gait and prefrontal cortex activity while walking in PD. A single-site, randomized, double-blind crossover trial examined effects of levodopa and donepezil in PD. Twenty PD participants were randomized, and 19 completed the trial. Participants were randomized to either levodopa + donepezil (5 mg) or levodopa + placebo treatments, with 2 weeks with treatment and a 2-week washout. The primary outcome was change in prefrontal cortex activity while walking, and secondary outcomes were change in gait and dual-task performance and attention. Levodopa decreased prefrontal cortex activity compared with off medication (effect size, −0.51), whereas the addition of donepezil reversed this decrease. Gait speed and stride length under single- and dual-task conditions improved with combined donepezil and levodopa compared with off medication (effect size, 1 for gait speed and 0.75 for stride length). Dual-task reaction time was quicker with levodopa compared with off medication (effect size, −0.87), and accuracy improved with combined donepezil and levodopa (effect size, 0.47). Cholinergic therapy, specifically donepezil 5 mg/day for 2 weeks, can alter prefrontal cortex activity when walking and improve secondary cognitive task accuracy and gait in PD. Further studies will investigate whether higher prefrontal cortex activity while walking is associated with gait changes. © 2020 International Parkinson and Movement Disorder Society     

A narrative review of gait training after stroke and a proposal for developing a novel gait training device that provides minimal assistance

Background: Gait impairment is common in stroke survivors. Recovery of walking ability is one of the most pressing objectives in stroke rehabilitation.

Objectives: Of this report are to briefly review recent progress in gait training after stroke including the use of partial body weight-supported treadmill training (PBWSTT) and robot-assisted step training (RAST), and propose a minimal assistance strategy that may overcome some of limitations of current RAST.

Methods: The literature review emphasizes a dilemma that recent randomized clinical trials did not support the use of RAST. The unsatisfactory results of current RAST clinical trials may be partially due to a lack of careful analysis of movement deficiencies and their relevance to gait training task specificity after stroke. Normal movement pattern is implied to be part of task specificity in the current RAST. Limitations of such task specificity are analyzed.

Results: Based on the review, we redefine an alternative set of gait training task specificity that represents a minimal assistance strategy in terms of assisted body movements and amount of assistance. Specifically, assistances are applied only to hip flexion and ankle dorsiflexion of the affected lower limb during swing phase. Furthermore, we propose a conceptual design of a novel device that may overcome limitations of current RAST in gait training after stroke. The novel device uses a pulling cable, either manually operated by a therapist or automated by a servomotor, to provide assistive forces to help hip flexion and ankle dorsiflexion of the affected lower limb during gait training.

Conclusion: The proposed minimal assistance strategy may help to design better devices for gait or other motor training.     

Frontopolar cortical inefficiency may underpin reward and working memory dysfunction in bipolar disorder

Abstract

Objectives. Emotional dysregulation in bipolar disorder is thought to arise from dysfunction within prefrontal cortical regions involved in cognitive control coupled with increased or aberrant activation within regions engaged in emotional processing. The aim of this study was to determine the common and distinct patterns of functional brain abnormalities during reward and working memory processing in patients with bipolar disorder. Methods. Participants were 36 euthymic bipolar disorder patients and 37 healthy comparison subjects matched for age, sex and IQ. Functional magnetic resonance imaging (fMRI) was conducted during the Iowa Gambling Task (IGT) and the n-back working memory task. Results. During both tasks, patients with bipolar disorder demonstrated a pattern of inefficient engagement within the ventral frontopolar prefrontal cortex with evidence of segregation along the medial-lateral dimension for reward and working memory processing, respectively. Moreover, patients also showed greater activation in the anterior cingulate cortex during the Iowa Gambling Task and in the insula during the n-back task. Conclusions. Our data implicate ventral frontopolar dysfunction as a core abnormality underpinning bipolar disorder and confirm that overactivation in regions involved in emotional arousal is present even in tasks that do not typically engage emotional systems.     

Specific relationship between prefrontal neuronal N-acetylaspartate and activation of the working memory cortical network in schizophrenia

OBJECTIVE: Abnormal activation of the dorsolateral prefrontal cortex and a related cortical network during working memory tasks has been demonstrated in patients with schizophrenia, but the responsible mechanism has not been identified. The present study was performed to determine whether neuronal pathology of the dorsolateral prefrontal cortex is linked to the activation of the working memory cortical network in patients with schizophrenia. METHOD: The brains of 13 patients with schizophrenia and 13 comparison subjects were studied with proton magnetic resonance spectroscopic ((1)H-MRS) imaging (to measure N-acetylaspartate as a marker of neuronal pathology) and with [(15)O]water positron emission tomography (PET) during performance of the Wisconsin Card Sorting Test (to measure activation of the working memory cortical network). An independent cohort of patients (N=7) was also studied in a post hoc experiment with (1)H-MRS imaging and with the same PET technique during performance of another working memory task (the "N-back" task). RESULTS: Measures of N-acetylaspartate in the dorsolateral prefrontal cortex strongly correlated with activation of the distributed working memory network, including the dorsolateral prefrontal, temporal, and inferior parietal cortices, during both working memory tasks in the two independent groups of patients with schizophrenia. In contrast, N-acetylaspartate in other cortical regions and in comparison subjects did not show these relationships. CONCLUSIONS: These findings directly implicate a population of dorsolateral prefrontal cortex neurons as selectively accounting for the activity of the distributed working memory cortical network in schizophrenia and complement other evidence that dorsolateral prefrontal cortex connectivity is fundamental to the pathophysiology of the disorder.     

Bilateral impairments in task-dependent modulation of the long-latency stretch reflex following stroke

ObjectiveModulation of the long-latency reflex (LLR) is important for sensorimotor control during interaction with different mechanical loads. Transcortical pathways usually contribute to LLR modulation, but the integrity of pathways projecting to the paretic and non-paretic arms of stroke survivors is compromised. We hypothesize that disruption of transcortical reflex pathways reduces the capacity for stroke survivors to appropriately regulate the LLR bilaterally.MethodsElbow perturbations were applied to the paretic and non-paretic arms of persons with stroke, and the dominant arm of age-matched controls as subjects interacted with Stiff or Compliant environments rendered by a linear actuator. Reflexes were quantified using surface electromyograms, recorded from biceps.ResultsLLR amplitude was significantly larger during interaction with the Compliant load compared to the Stiff load in controls. However, there was no significant change in LLR amplitude for the paretic or non-paretic arm of stroke survivors.ConclusionModulation of the LLR is altered in the paretic and non-paretic arms after stroke.SignificanceOur results are indicative of bilateral sensorimotor impairments following stroke. The inability to regulate the LLR may contribute to bilateral deficits in tasks that require precise control of limb mechanics and stability.     

The effect of apomorphine on regional cerebral blood flow in schizophrenia

A double-blind, placebo-controlled crossover study of the effects of apomorphine on regional cerebral blood flow (rCBF) during a prefrontal cortex activation task was undertaken to explore the role of dopamine on cortical function. The subjects were eight drug-free, chronically psychotic patients; six patients had schizophrenia. In each, apomorphine increased the relative prefrontal flow. The results suggest that enhanced prefrontal dopamine activity may reverse deficits in prefrontal cortex metabolism in schizophrenia.     

Endpoint accuracy of goal-directed ankle movements correlates to over-ground walking in stroke

ObjectivesGoal-directed movements are essential for voluntary motor control. The inability to execute precise goal-directed movements after stroke can impair the ability to perform voluntary functions, learn new skills, and hinder rehabilitation. However, little is known about how the accuracy of single-joint, goal-directed ankle movements relates to multi-joint, lower limb function in stroke. Here, we determined the impact of stroke on the accuracy of goal-directed ankle movements and its relation to over-ground walking.MethodsStroke (N = 28) and control (N = 28) participants performed (1) goal-directed ankle dorsiflexion movements to accurately match 9 degrees in 180 ms and (2) over-ground walking. During goal-directed ankle movements, we measured the endpoint error, position error, time error and the activation of the agonist and antagonist muscles. During over-ground walking, we measured the walking speed, paretic stride length, and cadence.ResultsThe stroke group demonstrated increased endpoint error than the controls. Increased endpoint error was associated with increased co-activation between agonist-antagonist muscles. Endpoint error was a significant predictor of walking speed and paretic stride length in stroke.ConclusionsImpaired accuracy of goal-directed, ankle movements is correlated to over-ground walking in stroke.SignificanceQuantifying accuracy of goal-directed ankle movements may provide insights into walking function post-stroke.     

Altered nerve excitability properties after stroke are potentially associated with reduced neuromuscular activation

ObjectiveTo determine limb differences in motor axon excitability properties in stroke survivors and their relation to maximal electromyographic (EMG) activity.MethodsThe median nerve was stimulated to record compound muscle action potentials (CMAP) from the abductor pollicis brevis (APB) in 28 stroke subjects (57.3 ± 7.5 y) and 24 controls (56.7 ± 9.3 y).ResultsParetic limb axons differed significantly from non-paretic limb axons including (1) smaller superexcitability and subexcitability, (2) higher threshold during subthreshold depolarizing currents, (3) greater accommodation (S3) to hyperpolarization, and (4) a larger stimulus-response slope. There were smaller differences between the paretic and control limbs. Responses in the paretic limb were reproduced in a model by a 5.6 mV hyperpolarizing shift in the activation voltage of Ih (the current activated by hyperpolarization), together with an 11.8% decrease in nodal Na⁺ conductance or a 0.9 mV depolarizing shift in the Na⁺ activation voltage. Subjects with larger deficits in APB maximal voluntary EMG had larger limb differences in excitability properties.ConclusionsStroke leads to altered modulation of Ih and altered Na⁺ channel properties that may be partially attributed to a reduction in neuromuscular activation.SignificancePlastic changes occur in the axon node and internode that likely influence axon excitability.     

Muscle force strategies for poststroke hemiparetic patients during gait

Background and Objective: Individuals who survive a stroke often display considerable gait impairments that occur in part due to inadequate muscle force production. This study aimed to investigate lower limb muscle forces in poststroke patients during walking.

Methods: Kinematics, kinetics, and electromyographic (EMG) measurements were performed on nine poststroke and healthy individuals walking at natural speed in a cross-sectional study. Recorded parameters were used in an EMG-driven model to estimate the forces exerted by the muscles around the knee and ankle joints during the stance (braking and propulsion) and swing phases.

Results: For hemiparetic patients, in comparison to healthy controls, the paretic side exhibited (i) lower forces generated by plantar-flexors and quadriceps respectively during the braking and propulsion phases, but (ii) higher knee-flexors forces during the propulsion phase. Regarding the non-paretic side, it displayed (i) higher forces generated by knee-flexors and quadriceps (only for the propulsion phase) forces during the stance phase, and (iii) higher plantar-flexors forces during the swing phase, in comparison to controls.

Conclusion: Reduced forces exerted by the plantar-flexors and the knee-extensors along with increased force generated by the knee-flexors on the paretic side give possible explanation for hemiparetic gait abnormalities. Increased muscle forces exerted by the non-paretic side might be a compensatory strategy to better support body weight and properly adjust the center of mass forward.