An fMRI Study of the Differences in Brain Activity During Active Ankle Dorsiflexion and Plantarflexion

Little is known regarding the differences in active cortical and subcortical systems during opposing movements of an agonist-antagonist muscle group. The objective of this study was to characterize the differences in cortical activation during active ankle dorsiflexion and plantarflexion using functional MRI (fMRI). Eight right-handed healthy adults performed auditorily cued right ankle dorsiflexions and plantarflexions during fMRI. Differences in activity patterns between dorsiflexion and plantarflexion during fMRI were assessed using between- and within-subject voxel-wise t-tests. Results indicated that ankle dorsiflexion recruited significantly more regions in left M1, the supplementary motor area (SMA) bilaterally, and right cerebellum. Both movements activated similar left hemisphere regions in the putamen and thalamus. Dorsiflexion activated additional areas in the right putamen. Results suggest that ankle dorsiflexion and plantarflexion may be controlled by both shared and independent neural circuitry. This has important implications for functional investigations of gait pathology and how rehabilitation may differentially affect each movement.     

Soleus muscle length, stretch reflex excitability, and the contractile properties of muscle in children and adults: a study of the functional joint angle

The influence of the joint angle on stretch reflex excitability of the soleus muscle at the ankle has been studied in 22 children aged 3.9 to 13.6 years and 9 adults aged 19 to 70 years. For all subjects, reflex EMG and mechanical twitch torque gain were trivial at resting plantar flexion. The reflex EMG gain reached a maximum between-15^o and-10^o of plantar flexion beyond the neutral angle, 0^o, denned as the foot at right angle to the tibia, diminishing steeply with further dorsiflexion. The reflex mechanical gain rose to a peak between 0^o and +10^o of dorsiflexion beyond neutral, declining steeply thereafter. By contrast, axonally stimulated muscle twitch torque increased serially up to +30^o dorsiflexion beyond neutral. For the soleus muscle, the optimal reflex neuromechanical angle lies approximately midway between the angle for optimal reflex EMG gain (in mild plantar flexion, at which the largest and strongest motor units can be activated) and the optimal muscle mechanical angle (at the extreme of soleus muscle dorsiflexion). These studies confirm that the excitability of the spinal alpha motor neuron pool in vivo is strongly influenced by muscle length and explain the variability in reflex excitability within and between subjects, if the joint angle is not controlled. They also indicate how posture influences movement, agreeing with the known function of the soleus muscle in the stance phase of gait and the modulation of motor unit recruitment during voluntary alternating movements at the ankle. Soleus muscle twitch characteristics show a fivefold to eightfold increase in peak force associated with a tenfold reduction in compliance in the first two decades of life and an apparent speeding up of twitch time in the first decade.     

Primary sensory and motor cortex activities during voluntary and passive ankle mobilization by the SHADE orthosis

This study investigates cortical involvement during ankle passive mobilization in healthy subjects, and is part of a pilot study on stroke patient rehabilitation. Magnetoencephalographic signals from the primary sensorimotor areas devoted to the lower limb were collected together with simultaneous electromyographic activities from tibialis anterior (TA). This was done bilaterally, on seven healthy subjects (aged 29 ± 7), during rest, left and right passive ankle dorsiflexion (imparted through the SHADE orthosis, O‐PM, or neuromuscular electrical stimulation, NMES‐PM), and during active isometric contraction (IC‐AM). The effects of focussing attention on ankle passive movements were considered. Primary sensory (FS_S1) and motor (FS_M1) area activities were discriminated by the Functional Source Separation algorithm. Only contralateral FS_S1 was recruited by common peroneal nerve stimulation and only contralateral FS_M1 displayed coherence with TA muscular activity. FS_M1 showed higher power of gamma rhythms (33–90 Hz) than FS_S1. Both sources displayed higher beta (14–32 Hz) and gamma powers in the left than in the right hemisphere. Both sources displayed a bilateral reduction of beta power during IC‐AM with respect to rest. Only FS_S1 beta band power reduced during O‐PM. No beta band modulation was observed of either source during NMES‐PM. Mutual FS_S1‐FS_M1 coherence in gamma2 band (61–90 Hz) showed a slight trend towards an increase when focussing attention during O‐PM. Somatosensory and motor counterparts of lower limb cortical representations were discriminated in both hemispheres. SHADE was effective in generating repeatable dorsiflexion and inducing primary sensory involvement similarly to voluntary movement. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

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

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

Ankle contractures and functional motor decline in Duchenne muscular dystrophy

IntroductionThis prospective, correlational pilot study investigated the relationship between ankle plantar flexion contractures and motor function in boys with Duchenne muscular dystrophy in British Columbia (BC), Canada.ParticipantsAmbulatory boys with Duchenne muscular dystrophy were recruited from BC Children’s Hospital, which follows everyone with Duchenne muscular dystrophy in BC ≤ 18 years of age (n = 14).MethodsSpearman and Pearson correlation coefficients were estimated to examine the association between the degree of ankle dorsiflexion range of motion and North Star Ambulatory Assessment scores and the degree of ankle dorsiflexion range and six-minute walk test distances.ResultsOur analysis showed a moderate correlation between the degree of ankle dorsiflexion range and North Star Ambulatory Assessment scores [rho (14) = 0.50; p = 0.070] and a weak correlation between ankle dorsiflexion range of motion and six-minute walk test distances [rho (13) = 0.08; p = 0.747], however neither result was statistically significant.DiscussionAlthough a significant relationship between ankle dorsiflexion range of motion and motor function was not found, the variability of ankle dorsiflexion range suggests challenges with preventing ankle contracture. This reinforces the importance of assessing ankle range of motion in boys with Duchenne muscular dystrophy with sufficient frequency to identify a need for additional interventions.     

Movement-related cortical potentials associated with voluntary relaxation of foot muscles.

OBJECTIVE: In our previous study of movement-related cortical potential (MRCP) in association with the voluntary relaxation of the hand muscle, Bereitschaftspotential (BP) was maximal at the vertex and symmetrically distributed, and Negative Slope (NS') was maximal over the contralateral central region. In order to clarify the generator sources of MRCP with voluntary muscle relaxation, we recorded MRCP in association with voluntary relaxation of the foot. METHODS: MRCP in association with plantar flexion of the foot caused by voluntary relaxation of the tibialis anterior muscle was recorded in 10 normal subjects. RESULTS: The BP started at about 1.7 s before the onset of the muscle relaxation, followed by NS' starting at about 650 ms before it. Both were maximal at the vertex and symmetrically distributed. There was no additional EEG activity in the lateral frontal areas, which are presumably located over the primary negative motor areas (PNMA). CONCLUSIONS: It is concluded that the voluntary muscle relaxation, similarly to the voluntary muscle contraction, involves the cortical preparatory activity at least in the primary motor area (M1) and probably the supplementary motor areas (SMAs). There is no evidence to suggest that the PNMA is also active prior to the voluntary muscle relaxation.     

Kinematic assessment of a functional role for recurrent inhibition and selective recruitment

It has been proposed that recurrent inhibition, which is presumed to act more powerfully on type S than on FR or FF motoneurons, and a selective recruitment order of synergistic motoneurons may function to prevent slowly contracting muscles from impeding rapid contractions. The possibility that such mechanical interactions do occur was investigated kinematically by analysis of plantar flexion in the rat hind limb under loaded and unloaded muscle conditions. The left limb was denervated to isolate the lateral gastrocnemius-soleus nerve and muscles. Plantar flexion was induced before and after soleus denervation by posterior tibial-nerve stimulation with the ankle in one of three positions: (i) resting (unloaded), (ii) dorsiflexed (held by a restraint bar), or (iii) with ankle position set by a load applied in series to the intact Achilles tendon. With the initial ankle position near maximal dorsiflexion, peak velocities of foot movements associated with passive elastic muscle properties approached one-half or more of the values achieved by active contractile mechanisms. Under unloaded and loaded conditions, no evidence was found in support of mechanical interference by the slower contracting soleus muscle of maximal lateral gastrocnemius shortening responses. Contributions of soleus tension to foot velocity and acceleration began to emerge with loads greater than 3 N. These findings are in agreement with previous reports that the slow-contracting soleus muscle, though fully activated, cannot contribute effectively to plantar flexion movements at speeds above a critical level.     

Cortical mechanism underlying externally cued gait initiation studied by contingent negative variation

In order to clarify the cortical mechanism underlying gait initiation, we examined the scalp distribution of the contingent negative variation (CNV) preceding externally cued gait initiation in a simple reaction-time paradigm in 10 healthy right-handed men, and compared the results with the CNV preceding simple foot dorsiflexion. A pair of auditory stimuli was given with an interstimulus (S1–S2) interval of 2 s and gait consisting of at least 3 steps was initiated with the right footstep as fast as possible in response to S2. Brisk dorsiflexion of the right foot was employed as a control task. It was found that the late CNV in the gait initiation task started about 1 s before S2, and was largest at Cz (−9.3 ± 3.1 μV) without clear asymmetry over the scalp. However, it was ill defined in the parietal area. In the foot dorsiflexion task, the late CNV was maximal at Cz (−7.1 ± 2.9 μV), and clearly seen also over the parietal area. The late CNV at Cz was significantly (P < 0.01) larger in the gait initiation than in the simple foot dorsiflexion. The amplitude of the late CNV preceding the foot dorsiflexion task was not significantly different between the sitting and the standing posture. In view of the results of previous invasive studies in both humans and animals which showed some frontal areas, including the supplementary motor area (SMA) and the primary motor cortex, as the generators of the late CNV, it is suggested that the cerebral cortex is active in initiation of externally triggered gait in a different way from the simple foot movement, and that bilateral SMAs may play a more important role in gait initiation than in simple foot movement.     

Assessment of regional blood flow in cerebral motor and sensory areas in patients with spinal cord injury

We assessed the presence and the degree of alteration of the regional blood flow (rCBF) as visualized by Tc-99m HMPAO brain rest SPECT in the sensory motor cortex and subcortical structure in spinal cord injury (SCI) patients, who suffered from various levels of motor and sensory function loss. Twenty-two patients (mean age: 42.1+/-13.4 years, 18 M, 4 F) and 11 control subjects (mean age: 32.2+/-6.4 years, 8 M, 3 F) participated in this study. The spinal cord injury group was consisted of 2 groups (14 paraplegic and 8 tetraplegic patients). The corticocortical rCBF ratios were calculated by using region of interests obtained from 34 cortical areas on coronal slices. Significantly reduced rCBF were measured from 11 cortical areas in tetraplegic patients and 11 cortical areas in paraplegic patients. Some of these areas were different in each group. In the tetraplegic group, significant reduction was observed in the following rCBF areas: left anterior cingulate gyrus, left medial supplementary motor area, bilateral front and back aspects of posterior cingulate gyrus, right lateral primary motor area, right medial primary sensory area, bilateral putamen, and right cerebellum. In the paraplegic group, reduced rCBF areas were as follows: bilateral anterior cingulate gyrus, right lateral supplementary motor area, left front aspect of posterior cingulate gyrus, left lateral primary motor area, bilateral back aspects of posterior cingulate gyrus, right medial primary sensory area, left lateral primary sensory area and bilateral putamen. In conclusion, in some of the movement-cortical and subcortical areas having significantly reduced blood flow in SCI may be helpful to demonstrate the disrupted areas of rCBF by SPECT. We believe that it may be useful if these findings should be considered during the evaluations related to the reorganization in SCI cases.     

Hand motor recovery after stroke: tuning the orchestra to improve hand motor function.

The motor deficits after stroke are not only the manifestation of the injured brain region, but rather the expression of the ability of the rest of the brain to maintain function. After a lesion in the primary motor cortex, parallel motor circuits might be activated to generate some alternative input to the spinal motoneurons. These parallel circuits may originate from areas such as the contralateral, undamaged primary motor area, bilateral premotor areas, bilateral supplementary motor areas, bilateral somatosensory areas, cerebellum, and basal ganglia. Most importantly, the efferent, cortico-spinal output pathways must be preserved for a desired behavioral result. Most of the recovery of function after a stroke may represent actual relearning of the skills with the injured brain. The main neural mechanisms underlying this relearning process after stroke involve shifts of distributed contributions across a specific neural network (fundamentally the network engaged in skill learning in the healthy). If these notions are indeed correct, then neuromodulatory approaches, such as transcranial magnetic stimulation, targeting these parallel circuits might be useful to limit injury and promote recovery after a stroke. This paper reviews the stroke characteristics that can predict a good recovery and compensations across brain areas that can be implemented after a stroke to accelerate motor function recovery.     

正常人手运动功能脑皮质定位的研究

目的 研究正常人手复杂运动时脑皮质的功能定位。方法 采用SIEMENS成像系统的EPI-Bolding程序，采集7例受试运动和静止状态的T1W图像共6个时相，应用相应软件分析得到差异信号图像，在T1W结构图像融合，并进行三维重建。结果 7例受试在执行握拳运动时，对侧皮质中央前回的第一运动区（Broadman 4区）均可见明显激活信号，对侧或双侧的补充运动区均有激活信号，2例运动前区激活，3例可见同侧中央前回运动皮质的激活信号。三维重建显示第一运动区的激活信号主要位于对侧中央沟的中外侧，补充运动区的激活信号位于运动前区（Broadman 6区）近正中的内侧面。结论 正常人手复杂运动时脑皮质运动网络被广泛激活，功能核磁共振的激活信号反映了脑的高级功能活动。     

Neural correlates of visuomotor adjustments during scaling of human finger movements

Visually guided finger movements include online feedback of current effector position to guide target approach. This visual feedback may be scaled or otherwise distorted by unpredictable perturbations. Although adjustments to visual feedback scaling have been studied before, the underlying brain activation differences between upscaling (visual feedback larger than real movement) and downscaling (feedback smaller than real movement) are currently unknown. Brain activation differences between upscaling and downscaling might be expected because within‐trial adjustments during upscaling require corrective backwards accelerations, whereas correcting for downscaling requires forward accelerations. In this behavioural and fMRI study we investigated adjustments during up‐ and downscaling in a target‐directed finger flexion–extension task with real‐time visual feedback. We found that subjects made longer and more complete within‐trial corrections for downscaling perturbations than for upscaling perturbations. The finger task activated primary motor (M1) and somatosensory (S1) areas, premotor and parietal regions, basal ganglia, and cerebellum. General scaling effects were seen in the right pre‐supplementary motor area, dorsal anterior cingulate cortex, inferior parietal lobule, and dorsolateral prefrontal cortex. Stronger activations for down‐ than for upscaling were observed in M1, supplementary motor area (SMA), S1 and anterior cingulate cortex. We argue that these activation differences may reflect differing online correction for upscaling vs. downscaling during finger flexion‐extension.     

Quantitative evaluation of electromyogram activity in rat extensor and flexor muscles immobilized at different lengths

Because immobilization of muscles in the "long" position mitigates the effects of inactivity and rapid wasting occurs when muscles are immobilized in the "short" position, a study was made of the EMG activity in the soleus (SOL)--an extensor muscle--and the tibialis anterior (TA)--a flexor muscle--in order to clarify the possible role of muscle function in modifying the course of disuse atrophy. EMG activity was recorded in the SOL and TA muscles in adult rats in which the ankle had been immobilized in a plaster cast either in plantar flexion or dorsiflexion. The number of action potentials per minute in samples of the EMG activity from control and immobilized muscles was assessed before, for 10 days during immobilization, and up to 9 days after removal of the cast. Immobilization in the short position (plantar flexion) led to a dramatic reduction in the EMG activity of the SOL (to 10% of the control). On the other hand, fixation of the SOL in the long position was without effect upon resting EMG activity. In the TA, EMG activity was exclusively phasic in character and corresponded to about 3% of that of the SOL. Neither the fixation of the ankle in plantar flexion nor dorsiflexion had any appreciable effect upon EMG activity in the TA. We conclude that, because immobilization in the lengthened position does not increase EMG activity in either extensor or flexor muscles, passive stretch appears to be the factor mainly responsible for mitigating the effects of disuse in this situation. On the other hand, when a typical extensor muscle (SOL) is immobilized in the shortened position and undergoes rapid wasting, an accessory role of decreased activity cannot be excluded.     

Responses of human primary sensorimotor and supplementary motor areas to internally triggered unilateral and simultaneous bilateral one‐digit movements. A high‐resolution EEG study

We modelled the responses of human primary sensorimotor areas and supplementary motor area to simple, self-initiated unilateral and simultaneous bilateral middle finger movements using a novel high-resolution electroencephalography technology. The results support the view that these cortical motor areas are involved in parallel and present similar activity in the preparation, initiation, and execution of the contralateral and bilateral movements. Furthermore, the left primary sensorimotor area (dominant hemisphere) appears to be activated more than the right primary sensorimotor area during the preparation and performance of the ipsilateral movements.     

Kinesthetic illusion of wrist movement activates motor-related areas.

We used positron emission tomography (PET) to test the hypothesis that illusory movement of the right wrist activates the motor-related areas that are activated by real wrist movements. We vibrated the tendons of the relaxed right wrist extensor muscles which elicits a vivid illusory palmar flexion. In a control condition, we vibrated the skin surface over the processes styloideus ulnae, which does not elicit the illusion, using the identical frequency (83 Hz). We provide evidence that kinesthetic illusory wrist movement activates the contralateral primary sensorimotor cortices, supplementary motor area (SMA) and cingulate motor area (CMA). These areas are also active when executing the limb movement.     

A stable late soleus EMG response elicited by cortical stimulation during voluntary ankle dorsiflexion

Transcranial electrical or magnetic stimulation was performed in 47 experiments on 42 normal adult subjects. Surface compound muscle action potentials were recorded from the antagonistic tibialis anterior (TA) and soleus (SOL) muscles. A stable late response recorded from SOL during voluntary ankle dorsiflexion is described and called soleus MEP-80. Its origin has been studied with different experimental procedures.

• 1.It is only obtained during active voluntary dorsiflexion of the ankle within 70–100 msec (mean 86.9 ± 6.4 msec) whereas passive dorsiflexion does not promote such a response. The size of SOL MEP-80 was always bigger than the primary SOL response.
• 2.A similar constant response has not been obtained during voluntary plantar flexion from SOL and TA muscles.
• 3.SOL MEP-80 is not changed significantly by the Jendrassik manoeuvre.
• 4.It is not obtained or is suppressed when the subject is sitting with the feet free in space. On the other hand, it is obtained when the subject is standing, especially when standing is made difficult.
• 5.SOL MEP-80 has not been obtained by brain-stem, spinal cord or root stimulation.
• 6.A later response of longer than 100 msec latency was sometimes obtained at rest but such an S100 soleus response was abolished or transformed to the SOL MEP-80 immediately during ankle dorsiflexion.
• 7.It is concluded that SOL MEP-80 is a polysynaptic extensor response related to postural mechanisms and originating through convergence of descending motor commands and peripheral sensory feedback.

     

Gait improvement after treadmill training in ischemic stroke survivors A critical review of functional MRI studies

Stroke survivors often present with abnormal gait, movement training can improve the walking performance post-stroke, and functional MRI can objectively evaluate the brain functions before and after movement training. This paper analyzes the functional MRI changes in patients with ischemic stroke after treadmill training with voluntary and passive ankle dorsiflexion. Functional MRI showed that there are some changes in some regions of patients with ischemic stroke including primary sensorimotor cortex, supplementary motor area and cingulate motor area after treadmill training. These findings suggest that treadmill training likely improves ischemic stroke patients’ lower limb functions and gait performance and promotes stroke recovery by changing patients’ brain plasticity; meanwhile, the novel treadmill training methods can better training effects.     

Spinal and supraspinal mechanisms affecting torque development at different joint angles

Introduction: We examined the neural mechanisms responsible for plantar flexion torque changes at different joint positions. Methods: Nine subjects performed maximal voluntary contractions (MVC) at 6 ankle–knee angle combinations [3 ankle angles (dorsiflexion, anatomic position, plantar flexion) and 2 knee angles (flexion, full extension)]. Neural mechanisms were determined by V‐wave, H‐reflex (at rest and during MVC), and electromyography during MVC (RMS), normalized to the muscle compound action potential (V/M_sup, H_max/M_max, H_sup/M_sup and RMS/M_sup) and voluntary activation (VA), while muscle function was assessed by doublet amplitude. Results: MVC and doublet amplitude were significantly lower at plantar flexion (P < 0.01), while VA was significantly lower at dorsiflexion and full knee extension (P < 0.05). V/M_sup and RMS/M_sup were significantly lower at knee extension (P < 0.01), while H_sup/M_sup was not affected by joint angle. Conclusions: These results indicate that joint positions leading to muscle lengthening produce reduced neural drive, due mainly to supraspinal mechanisms. Muscle Nerve 53 : 626–632, 2016     

Effect of kinesthetic illusion induced by visual stimulation on ankle dorsiflexion dysfunction in a stroke patient: ABAB single-case design

ABSTRACT

The purpose of this study was to investigate the effect of simultaneous intervention with the kinesthetic illusion induced by visual stimulation (KiNvis) and voluntary exercise on ankle dorsiflexion dysfunction in a patient with right-sided stroke hemiparesis. Within an ABAB single-case design, we conducted two phases each lasting five days. Phase A represented the baseline during which only voluntary ankle dorsiflexion (VAD) was performed. Phase B involved simultaneous performance of VAD and KiNvis. We measured the angle of ankle joint dorsiflexion (AJD), and the 10 m maximum walking speed (10MWS). AJD and 10MWS were significantly improved in phase B.     

不同人群踝关节跖屈肌群肌肉形态与力量的相关性

背景：骨骼肌肌肉形态与力量关系密切,采用CT、核磁共振等仪器对人体骨骼肌进行活体形态测量,结合相关肌肉力量测量手段探索两者之间相关关系的报道尚不多见。 目的：对比观察不同人群肌肉形态与力量的差异,探讨踝关节跖屈肌群形态特征与肌肉收缩力量之间的关系。 设计、时间及地点：对比观察,于2006-05/12在中国医科大学附属第二医院完成。 对象：选择普通男性青年学生14人作为对照组,测试前未专门从事过力量训练;另选健将级速滑运动员10人作为运动组。所有测试对象试验期间踝关节均无损伤。 方法：采用螺旋CT对受试对象双侧小腿进行不间断连续扫描,影像分析采用Xiphoid CT专用图像分析软件,由CT图像计算得出小腿围、踝关节跖屈肌横截面积,根据体视学原理采用数值积分法计算跖屈肌群体积。采用CYBEX-NORM型多关节等速测力系统对踝关节跖屈肌群进行60,120,180,240,300 (°)/s不同角速度下的等速测试。 主要观察指标：①各组受试者跖屈肌形态及不同角速度下跖屈峰力矩和跖屈相对峰力矩的变化。②各组受试者不同角速度下跖屈峰力矩与跖屈肌群体积、最大横截面积、小腿围相关性。 结果：①与对照组相比,运动组跖屈肌最大横断面积、体积和小腿围均显著增大(P < 0.05)。在踝关节等速向心测试中,运动组的跖屈向心峰力矩在每一个角速度下均显著高于对照组(P < 0.05),但随着关节运动角速度的增加,对照组和运动组的跖屈向心峰力矩都相应地减小,②在不同的角速度下,跖屈肌群最大横截面积、肌肉体积、小腿围与跖屈峰力矩之间均具有显著的正相关性(r > 0.725,P < 0.05~0.01)。 结论：跖屈肌群峰力矩变化趋势与肌肉形态相一致,肌肉形态可作为观测肌力变化的一个重要参考指标。