Ankle dorsiflexion as an fMRI paradigm to assay motor control for walking during rehabilitation

Spinal and brain control of human walking: implications for retraining of walking

In this update, the authors will discuss evidence for both spinal and brain regulation of walking in humans. They will consider the sensory control of walking in young babies and spinal cord-injured adults, two models with weak descending input from the brain, to suggest that subcortical structures are important in shaping walking behavior. Based on evidence from development, the authors suggest that the primitive pattern of walking seen in babies forms the base upon which additional features are added by supraspinal input as independent walking develops. Increasing evidence suggests the motor cortex is important in the control of level-ground walking in adults, in contrast to quadrupeds. This brain input seems particularly important for distal flexors in the leg. Finally, the authors will consider evidence that the recovery of walking after incomplete spinal cord injuries is dependent on the presence of descending input from the motor cortex and our ability to strengthen that input. These findings imply that training methods for improving walking after injury to the nervous system must promote the involvement of both spinal and brain circuits.

Watching Your Foot Move--An fMRI Study of Visuomotor Interactions during Foot Movement

The objective of this study was to investigate brain areas involved in distinguishing sensory events caused by self-generated movements from similar sensory events caused by externally generated movements using functional magnetic resonance imaging. Subjects performed 4 types of movements: 1) self-generated voluntary movement with visual feedback, 2) externally generated movement with visual feedback, 3) self-generated voluntary movement without visual feedback, and 4) externally generated movement without visual feedback, this design. This factorial design makes it possible to study which brain areas are activated during self-generated ankle movements guided by visual feedback as compared with externally generated movements under similar visual and proprioceptive conditions. We found a distinct network, comprising the posterior parietal cortex and lateral cerebellar hemispheres, which showed increased activation during visually guided self-generated ankle movements. Furthermore, we found differential activation in the cerebellum depending on the different main effects, that is, whether movements were self- or externally generated regardless of visual feedback, presence or absence of visual feedback, and activation related to proprioceptive input.

Lateralization of brain activity during lower limb joints movement. An fMRI study

Studies of unilateral finger movement in right-handed subjects have shown asymmetrical patterns of activation in primary motor cortex and subcortical regions. In order to investigate the existence of an analogous pattern during lower limb joints movements, functional magnetic resonance imaging (fMRI) was used. Eighteen healthy, right leg dominant volunteers participated in a motor block design study, performing unilateral right and left repetitive knee, ankle and toes flexion/extension movements. Aiming to relate lower limb joints activation to the well-described patterns of finger movement, serial finger-to-thumb opposition was also assessed. All movements were auditory paced at 72 beats/min (1.2 Hz). Brain activation during movement of the nondominant joints was more bilateral than during the same movement performed with the dominant joints. Finger movement had a stronger lateralized pattern of activation in comparison with lower limb joints, implying a different functional specialization. Differences were also evident between the joints of the lower limb. Ankle and toes movements elicited the same extend of MR signal change in the majority of the examined brain regions, whereas knee joint movement was associated with a different pattern. Finally, lateralization index in primary sensorimotor cortex and basal ganglia was significantly affected by the main effect of dominance, whereas the lateralization index in cerebellum was significantly affected by the joint main effect, demonstrating a lateralization index increase from proximal to distal joints.

Motor imagery of walking following training in locomotor attention. The effect of ‘the tango lesson’

The hypothesis of this study is that focusing attention on walking motor schemes could modify sensorimotor activation of the brain. Indeed, gait is a learned automated process, mostly regulated by subcortical and spinal structures. We examined the functional changes in the activity of the cerebral areas involved in locomotor imagery tasks, before and after one week of training consisting of physical and mental practice. The aim of the training was to focus the subject's conscious attention on the movements involved in walking. In our training, subjects were asked to perform basic tango steps, which require specific ways of walking; each tango lesson ended with motor imagery training of the performed steps. The results show that training determines an expansion of active bilateral motor areas during locomotor imagery. This finding, together with a reduction of visuospatial activation in the posterior right brain, suggests a decreased role of visual imagery processes in the post-training period in favor of motor-kinesthetic ones.

Combined Task-Specific Training and Strengthening Effects On Locomotor Recovery Post-Stroke

BACKGROUND AND PURPOSE

Task-specific and strength training have demonstrated efficacy as therapeutic interventions poststroke. The intent of this case study is to describe outcomes associated with a therapy program that combines task-specific and strength training in an individual post-stroke and to discuss some possible mechanisms and modulating factors that may affect post-stroke neurologic recovery and responsiveness to intervention.

CASE DESCRIPTION

The participant was a 38-year-old female with right middle cerebral artery stroke, evaluated 15 months postonset. She ambulated independently with an ankle-foot orthosis and straight cane. Her free and fast overground velocity was 0.50 m/s and 0.62 m/s, respectively. Body-weight supported treadmill training and a limb-loaded cycling exercise were alternated over 24 treatments sessions (4 times/wk for 6 wks). Measurements were taken pre-, post-treatment, and at a 6-mo follow-up. Instrumented gait and motion analysis with fine-wire EMG recording of LE muscle activity occurred pre- and post-treatment.

OUTCOMES

Post-treatment, walking speed increased 18% for free--(0.59 m/ s) and 14.4% for fast-velocity (0.71 m/s); 6-min walking distance increased 4% (184.4 m). At 6-mos, continued improvements in all walking outcomes were evident. Gait and motion analysis revealed that functional locomotor recovery was associated with increases in magnitude of paretic leg gluteus maximus and gluteus medius activation during gait. Motion analysis confirmed an increase of hip and knee extension motions throughout stance and swing.

DISCUSSION

For the person in this case clinically meaningful changes in walking function were associated with a combined therapeutic program that included both task-specific and LE strength training. Possible mechanisms associated with response to therapy were related to improved motor unit activation associated with increased strength in key muscles used in gait.

Effects of motor imagery training after chronic, complete spinal cord injury

Abnormalities in brain motor system function are present following spinal cord injury (SCI) and could reduce effectiveness of restorative interventions. Motor imagery training, which can improve motor behavior and modulate brain function, might address this concern but has not been examined in subjects with SCI. Ten subjects with SCI and complete tetra-/paraplegia plus ten healthy controls underwent assessment before and after 7 days of motor imagery training to tongue and to foot. Motor imagery training significantly improved the behavioral outcome measure, speed of movement, in non-paralyzed muscles. Training was also associated with increased fMRI activation in left putamen, an area associated with motor learning, during attempted right foot movement in both groups, despite foot movements being present in controls and absent in subjects with SCI. This fMRI change was absent in a second healthy control group serially imaged without training. In subjects with SCI, training exaggerated, rather than normalized, baseline derangement of left globus pallidus activation. The current study found that motor imagery training improves motor performance and alters brain function in subjects with complete SCI despite lack of voluntary motor control and peripheral feedback. These effects of motor imagery training on brain function have not been previously described in a neurologically impaired population, and were similar to those found in healthy controls. Motor imagery might be of value as one component of a restorative intervention.

Human treadmill walking needs attention

BACKGROUND

The aim of the study was to assess the attentional requirements of steady state treadmill walking in human subjects using a dual task paradigm. The extent of decrement of a secondary (cognitive) RT task provides a measure of the attentional resources required to maintain performance of the primary (locomotor) task. Varying the level of difficulty of the reaction time (RT) task is used to verify the priority of allocation of attentional resources.

METHODS

11 healthy adult subjects were required to walk while simultaneously performing a RT task. Participants were instructed to bite a pressure transducer placed in the mouth as quickly as possible in response to an unpredictable electrical stimulation applied on the back of the neck. Each subject was tested under five different experimental conditions: simple RT task alone and while walking, recognition RT task alone and while walking, walking alone. A foot switch system composed of a pressure sensitive sensor was placed under the heel and forefoot of each foot to determine the gait cycle duration.

RESULTS

Gait cycle duration was unchanged (p > 0.05) by the addition of the RT task. Regardless of the level of difficulty of the RT task, the RTs were longer during treadmill walking than in sitting conditions (p < 0.01) indicating that an increased amount of resources are required for the maintainance of walking performance on a treadmill at a steady state. No interaction (p > 0.05) was found between the attentional demand of the walking task and the decrement of performance found in the RT task under varying levels of difficulty. This finding suggests that the healthy subjects prioritized the control of walking at the expense of cognitive performance.

CONCLUSION

We conclude that treadmill walking in young adults is not a purely automatic task. The methodology and outcome measures used in this study provide an assessment of the attentional resources required by walking on the treadmill at a steady state.

Neuromuscular electric stimulation effect on lower-extremity motor recovery and gait kinematics of patients with stroke: a randomized controlled trial

OBJECTIVE

To evaluate the effects of neuromuscular electric stimulation (NMES) of the tibialis anterior muscle on motor recovery and gait kinematics of patients with stroke.

DESIGN

Randomized, controlled, assessor-blinded trial.

SETTING

Rehabilitation ward and gait laboratory of a university hospital.

PARTICIPANTS

A total of 25 consecutive inpatients with stroke (mean age, 55y), all within 6 months poststroke and without volitional ankle dorsiflexion.

INTERVENTION

Both the NMES group (n=12) and the control group (n=13) participated in a conventional stroke rehabilitation program, 5 days a week for 4 weeks. The NMES group also received 10 minutes of NMES to the tibialis anterior muscle of the paretic limb.

MAIN OUTCOME MEASURES

Brunnstrom stages of motor recovery and kinematic characteristics of gait.

RESULTS

Brunnstrom stages improved significantly in both groups (P<.05). In total, 58% of the NMES group and 61% of the control group gained voluntary ankle dorsiflexion. Between-group difference of percentage change was not significant (P>.05). Gait kinematics was improved in both groups, but the difference between groups was not significant.

CONCLUSIONS

NMES of the tibialis anterior muscle combined with a conventional stroke rehabilitation program was not superior to a conventional stroke rehabilitation program alone, in terms of lower-extremity motor recovery and gait kinematics.

Preserved aspects of cortical foot control in paraplegia

While several recent imaging studies confirm that motor foot areas can still be activated in complete and chronic paraplegia, it remains unclear whether their functionality is also maintained or declines after years of "non-use". Force control is one of the most important and best investigated functions within the motor cortex. It has been repeatedly reported that the motor cortex is more active when higher forces have to be applied. We thus addressed the question of preserved cortical functions by comparing motor force control patterns in the event-related potentials of 10 motor complete paraplegic subjects and 10 controls after attempted (paraplegic patients)/executed (healthy controls) ballistic foot movements with three different force levels. In addition to the peak amplitudes reflecting force levels, peak latencies were also investigated to elucidate timing as another functional aspect of motor control. No significant group difference was found for the peak latencies, indicating that the timing of motor cortical activation is preserved. Concerning amplitudes, we found preserved cortical modulation of higher forces but distorted low force modulation, especially early after injury. These findings thus suggest that important aspects of cortical control over paralyzed limbs are maintained despite years of "non-use".

Motor Cortex Activation During Treatment May Predict Therapeutic Gains in Paretic Hand Function After Stroke

Background and Purpose— Functional brain imaging after stroke offers insight into motor network adaptations. This exploratory study examined whether motor cortical activation captured during arm-focused therapy can predict paretic hand functional gains.

Methods— Eight hemiparetic patients had serial functional MRI (fMRI) while performing a pinch task before, midway, and after 2 weeks of constraint-induced therapy. The Wolf Motor Function Test (WMFT) was performed before and after intervention.

Results— There was a linear reduction in ipsilateral (contralesional) primary motor (M1) activation (voxel counts) across time. The midpoint M1 Laterality Index anticipated post-therapeutic change in time to perform the WMFT. The change in ipsilateral M1 voxel count (pre- to mid-) correlated with the change in mean WMFT time (pre- to post-).

Conclusions— The relationship between brain activation during treatment and functional gains suggests a use for serial fMRI in predicting the success and optimal duration for a focused therapeutic intervention.

Functional response to active and passive ankle movements with clinical correlations in patients with primary progressive multiple sclerosis

Patients with multiple sclerosis (MS) activate a more diffuse cortical network than do healthy subjects when they perform motor tasks. This brain functional reorganisation might contribute to the limiting of disability, but it is unclear whether there is a loss of regional activation in more advanced disease. The aim of this study was to assess whether functional reorganisation diminishes in more disabled patients with primary progressive (PP) MS. The differences in the fMRI response to active and passive movements of the dominant ankle of 13 patients and 16 controls were assessed. The relationships between functional activation and disability and brain lesion load and atrophy were investigated.Patients showed greater fMRI activation than controls with passive movements in the superior temporal gyrus, rolandic operculum, and putamen. The fMRI response to active and passive movements in the ipsilateral inferior frontal gyrus was lower in patients with greater disability and greater brain T2 lesion load, respectively. Furthermore, the fMRI activation with active movements in the contralateral cerebellum was lower in patients with worse mobility. The increased activity with passive movements in regions that participate in sensori-motor integration, such as the putamen, reflects true functional reorganisation, since passive movements induce brain activation through sensory afferents only. The inverse correlation between the fMRI response in regions that are associated with motor control, and clinical or MRI measures of disease progression, suggests that there is a loss of distributed activation in more disabled patients. This may inform future treatment strategies.

Rehabilitation and functional neuroimaging dose-response trajectories for clinical trials

BACKGROUND

In clinical trials, behavioral outcomes and physiological measures of activity-dependent plasticity that evolve with task-oriented therapies may fail to reach statistical significance. When significant, clinical effectiveness may not be robust enough to alter professional practices.

OBJECTIVE

Provide the conceptual basis for a research design to optimize the effect of an experimental treatment.

METHODS

Literature review.

RESULTS

Research designs usually do not take into consideration the dynamic state of each subject's potential responsiveness to an intervention. Providing a rational, rather than convenient, intensity and duration of therapy may remedy this potential confounder for clinical trials. To determine whether a most effective dose of a therapy exists, investigators could assess subjects before the intervention, administer interim measures at planned intervals, and continue the intervention until the primary behavioral outcomes or functional imaging parameters or both reach a plateau for at least 15 h of additional treatment.

CONCLUSION

Promising interventions ought to be continued in phase II/III trials until subjects reach an asymptote in the primary outcome for behavioral gains. For neuroimaging studies that aim to correlate brain-behavior measures during rehabilitation, the specific intervention should also continue until behavioral gains and cerebral adaptations have attained a persistent plateau. Future trials can investigate whether functional neuroimaging performed in parallel with repeated behavioral assessments can better inform researchers about the optimal duration of an experimental therapy and a subject's maximal capacity for intervention-induced cerebral reorganization.

Effects of treadmill exercise on transcranial magnetic stimulation-induced excitability to quadriceps after stroke

OBJECTIVE

To determine characteristics of transcranial magnetic stimulation (TMS)-induced measures of central motor excitability to the paretic and nonparetic quadriceps muscles of chronic hemiparetic stroke patients in the context of a short-term, submaximal bout treadmill exercise.

DESIGN

Cross-sectional.

SETTING

Motor control and gait biomechanics laboratory.

PARTICIPANTS

Convenience sample of 11 patients including cohorts of treadmill untrained (n=8) and trained (n=3) stroke patients with chronic hemiparetic gait.

INTERVENTION

Short-term submaximal treadmill exercise.

MAIN OUTCOME MEASURES

Thresholds, amplitudes and latencies of TMS-induced motor evoked potentials at vastus medialis in paretic and nonparetic lower extremities.

RESULTS

Baseline characteristics of the motor evoked potentials (MEPs) show significantly higher motor thresholds, longer latencies, and reduced amplitudes on the paretic side. In cross-sectional comparisons a group of treadmill-trained patients had greater paretic MEP amplitude changes after treadmill exercise versus paretic MEP responses from a group of untrained patients.

CONCLUSIONS

These results indicate that treadmill training for 3 months or more may alter responsiveness of the lower-extremity central motor pathways to a short-term treadmill stimulus.

Opening the black box of post-stroke rehabilitation: stroke rehabilitation patients, processes, and outcomes

DeJong G, Horn SD, Conroy B, Nichols D, Healton EB. Opening the black box of post-stroke rehabilitation: stroke rehabilitation patients, processes, and outcomes. This article introduces the journal's supplement devoted to the methods and findings of the 7-site Post-Stroke Rehabilitation Outcomes Project (PSROP), a study designed to provide a very granular in-depth understanding of stroke rehabilitation practice and how practice is related to outcomes. The article summarizes current knowledge about the effectiveness of post-stroke rehabilitation, outlines where the PSROP fits into the broader traditions of stroke rehabilitation outcomes research, underscores the study's methodologic innovations, and summarizes the scope of the articles that follow.

Identifying brain regions for integrative sensorimotor processing with ankle movements

The objective of this study was to define cortical and subcortical structures activated during both active and passive movements of the ankle, which have a fundamental role in the physiology of locomotion, to improve our understanding of brain sensorimotor integration. Sixteen healthy subjects, all right-foot dominant, performed a dorsi-plantar flexion task of the foot using a custom-made wooden manipulandum, which enabled measurements of the movement amplitude. All subjects underwent a training session, which included surface electromyography, and were able to relax completely during passive movements. Patterns of activation during active and passive movements and differences between functional MRI (fMRI) responses for the two types of movement were assessed. Regions of common activation during the active and passive movements were identified by conjunction analysis. We found that passive movements activated cortical regions that were usually similar in location to those activated by active movements, although the extent of the activations was more limited with passive movements. Active movements of both feet generated greater activation than passive movements in some regions (such as the ipsilateral primary motor cortex) identified in previous studies as being important for motor planning. Common activations during active and passive movements were found not only in the contralateral primary motor and sensory cortices, but also in the premotor cortical regions (such as the bilateral rolandic operculum and contralateral supplementary motor area), and in the subcortical regions (such as the ipsilateral cerebellum and contralateral putamen), suggesting that these regions participate in sensorimotor integration for ankle movements. In future, similar fMRI studies using passive movements have potential to elucidate abnormalities of sensorimotor integration in central nervous system diseases that affect motor function.

Identifying brain regions for integrative sensorimotor processing with ankle movements

The objective of this study was to define cortical and subcortical structures activated during both active and passive movements of the ankle, which have a fundamental role in the physiology of locomotion, to improve our understanding of brain sensorimotor integration. Sixteen healthy subjects, all right-foot dominant, performed a dorsi-plantar flexion task of the foot using a custom-made wooden manipulandum, which enabled measurements of the movement amplitude. All subjects underwent a training session, which included surface electromyography, and were able to relax completely during passive movements. Patterns of activation during active and passive movements and differences between functional MRI (fMRI) responses for the two types of movement were assessed. Regions of common activation during the active and passive movements were identified by conjunction analysis. We found that passive movements activated cortical regions that were usually similar in location to those activated by active movements, although the extent of the activations was more limited with passive movements. Active movements of both feet generated greater activation than passive movements in some regions (such as the ipsilateral primary motor cortex) identified in previous studies as being important for motor planning. Common activations during active and passive movements were found not only in the contralateral primary motor and sensory cortices, but also in the premotor cortical regions (such as the bilateral rolandic operculum and contralateral supplementary motor area), and in the subcortical regions (such as the ipsilateral cerebellum and contralateral putamen), suggesting that these regions participate in sensorimotor integration for ankle movements. In future, similar fMRI studies using passive movements have potential to elucidate abnormalities of sensorimotor integration in central nervous system diseases that affect motor function.

Clinical practice. Rehabilitation after stroke

A 66-year-old man was suddenly unable to speak, follow directions, or move his right arm and leg. He received tissue plasminogen activator within 90 minutes. Four days later, his speech was limited to effortful answers of yes or no. He could not walk or use his right arm, and self-care tasks required maximal assistance. What advice would you offer him and his family regarding rehabilitation for his disabilities?

Neurobiology of rehabilitation

Rehabilitation aims to lessen the physical and cognitive impairments and disabilities of patients with stroke, multiple sclerosis, spinal cord or brain injury, and other neurologic diseases. Conventional approaches beyond compensatory adjustments to disability may be augmented by applying some of the myriad experimental results about mechanisms of intrinsic biological changes after injury and the effects of extrinsic manipulations on spared neuronal assemblies. The organization and inherent adaptability of the anatomical nodes within distributed pathways of the central nervous system offer a flexible substrate for treatment strategies that drive activity-dependent plasticity. Opportunities for a new generation of approaches are manifested by rodent and non-human primate studies that reveal morphologic and physiologic adaptations induced by injury, by learning-associated practice, by the effects of pharmacologic neuromodulators, by the behavioral and molecular bases for enhancing activity-dependent synaptic plasticity, and by cell replacement, gene therapy, and regenerative biologic strategies. Techniques such as functional magnetic resonance imaging and transcranial magnetic stimulation will help determine the most optimal physiologic effects of interventions in patients as the cortical representations for skilled movements and cognitive processes are modified by the combination of conventional and biologic therapies. As clinicians digest the finer details of the neurobiology of rehabilitation, they will translate laboratory data into controlled clinical trials. By determining how much they can influence neural reorganization, clinicians will extend the opportunities for neurorestoration.

Strategies for stroke rehabilitation

Rehabilitation after hemiplegic stroke has typically relied on the training of patients in compensatory strategies. The translation of neuroscientific research into care has led to new approaches and renewed promise for better outcomes. Improved motor control can progress with task-specific training incorporating increased use of proximal and distal movements during intensive practice of real-world activities. Functional gains are incorrectly said to plateau by 3-6 months. Many patients retain latent sensorimotor function that can be realised any time after stroke with a pulse of goal-directed therapy. The amount of practice probably best determines gains for a given level of residual movement ability. Clinicians should encourage patients to build greater strength, speed, endurance, and precision of multijoint movements on tasks that increase independence and enrich daily activity. Imaging tools may help clinicians determine the capacity of residual networks to respond to a therapeutic approach and help establish optimal dose-response curves for training. Promising adjunct approaches include practice with robotic devices or in a virtual environment, electrical stimulation to increase cortical excitability during training, and drugs to optimise molecular mechanisms for learning. Biological strategies for neural repair may augment rehabilitation in the next decade.