William E. McIlroy

Evaluation of gait symmetry after stroke: a comparison of current methods and recommendations for standardization.

Symmetry is a gait characteristic that is increasingly measured and reported, particularly in the stroke patient population. However, there is no accepted standard for assessing symmetry making it difficult to compare across studies and establish criteria to guide clinical decision making. This study compares the most common expressions of spatiotemporal gait symmetry to describe post-stroke gait and makes recommendations regarding the most suitable measure for standardization. The following symmetry equations were compared: symmetry ratio, symmetry index, gait asymmetry and symmetry angle using step length, swing time, stance time, double support time and an intra-limb ratio of swing: stance time. Comparisons were made within a group of 161 community-dwelling, ambulatory individuals with stroke and 81 healthy adults as a reference group. Our analysis supports the recommendations of the symmetry ratio as the equation for standardization and step length, swing time and stance time as the gait parameters to be used in the equation. Future work should focus on establishing the intra-individual variability of these measures and linking them to mechanisms of gait dysfunction.

Gait Asymmetry in Community-Ambulating Stroke Survivors

OBJECTIVES To determine the prevalence and severity of asymmetry among independently ambulating stroke survivors and to establish the association between velocity and asymmetry. DESIGN Descriptive analysis. SETTING Research gait laboratory in a Canadian hospital. PARTICIPANTS Community-dwelling, independently ambulating participants (N=54) with chronic stroke. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Overground gait velocity, symmetry ratios for temporal and spatial step parameters, and motor impairment of the foot and leg. Spatiotemporal parameters were collected with a pressure-sensitive mat. Motor impairment was measured clinically with the Chedoke-McMaster Stroke Assessment. RESULTS Thirty (55.5%) participants showed statistically significant temporal asymmetry and 18 (33.3%) exhibited statistically significant spatial asymmetry. Preferred velocity was negatively associated with temporal asymmetry (r=-.583, df=52, P<.001) but not spatial asymmetry (r=-.146, df=52, P=.29). Temporal asymmetry was also associated with motor recovery of the leg (r=-.644, df=35, P<.001) and foot (r=-.628, df=35, P<.001). CONCLUSIONS The results of the current study illustrate that temporal asymmetry can be found in many independently ambulating stroke patients. The work highlights the need for a standard assessment of poststroke gait symmetry in light of the complex relationship with motor impairment and velocity.

The role of plantar cutaneous mechanoreceptors in the control of compensatory stepping reactions evoked by unpredictable, multi-directional perturbation

The role of plantar pressure sensation in controlling compensatory stepping was explored via hypothermic anesthesia of the foot soles, in 10 healthy young adults. Stepping reactions were evoked by unpredictable platform translation in forward, backward and lateral directions. The findings suggest three specific direction- and phase-dependent roles for the plantar cutaneous afferents: (1) sensing posterior stability limits during initiation of backward steps, (2) sensing and controlling heel-contact and subsequent weight transfer during termination of forward steps, and (3) maintaining stability during the prolonged swing phase of lateral crossover steps.

Sensori-sensory afferent conditioning with leg movement: gain control in spinal reflex and ascending paths.

Studies are reviewed, predominantly involving healthy humans, on gain changes in spinal reflexes and supraspinal ascending paths during passive and active leg movement. The passive movement research shows that the pathways of H reflexes of the leg and foot are down-regulated as a consequence of movement-elicited discharge from somatosensory receptors, likely muscle spindle primary endings, both ipsi- and contralaterally. Discharge from the conditioning receptors in extensor muscles of the knee and hip appears to lead to presynaptic inhibition evoked over a spinal path, and to long-lasting attenuation when movement stops. The ipsilateral modulation is similar in phase to that seen with active movement. The contralateral conditioning does not phase modulate with passive movement and modulates to the phase of active ipsilateral movement. There are also centrifugal effects onto these pathways during movement. The pathways of the cutaneous reflexes of the human leg also are gain-modulated during active movement. The review summarizes the effects across muscles, across nociceptive and non-nociceptive stimuli and over time elapsed after the stimulus. Some of the gain changes in such reflexes have been associated with central pattern generators. However, the centripetal effect of movement-induced proprioceptive drive awaits exploration in these pathways. Scalp-recorded evoked potentials from rapidly conducting pathways that ascend to the human somatosensory cortex from stimulation sites in the leg also are gain-attenuated in relation to passive movement-elicited discharge of the extensor muscle spindle primary endings. Centrifugal influences due to a requirement for accurate active movement can partially lift the attenuation on the ascending path, both during and before movement. We suggest that a significant role for muscle spindle discharge is to control the gain in Ia pathways from the legs, consequent or prior to their movement. This control can reduce the strength of synaptic input onto target neurons from these kinesthetic receptors, which are powerfully activated by the movement, perhaps to retain the opportunity for target neuron modulation from other control sources.

Cognitive demands and cortical control of human balance-recovery reactions.

SummaryA traditional view has been that balance control occurs at a very automatic level, primarily involving the spinal cord and brainstem; however, there is growing evidence that the cerebral cortex and cognitive processing are involved in controlling specific aspects of balance. The purpose of this review is to summarize recent literature pertaining to the cognitive demands and cortical control of balance-recovery reactions, focussing on five emerging sources of evidence: 1) dual-task studies demonstrating that concurrent performance of cognitive and balance-recovery tasks leads to interference effects; 2) dual-task studies that have examined the temporal dynamics associated with the reallocation of cognitive resources to the balance-recovery task; 3) visual attention studies that have inferred contributions of visual attention based on gaze measurements and/or manipulations to occlude vision; 4) measurements of brain potentials evoked by postural perturbation; and 5) use of transcranial magnetic stimulation to alter contributions from specific cortical areas.

Rehabilitation of Reaching and Grasping Function in Severe Hemiplegic Patients Using Functional Electrical Stimulation Therapy

Objective. The aim of this study was to establish the efficacy of a therapeutic intervention based on functional electrical stimulation (FES) therapy to improve reaching and grasping function after severe hemiplegia due to stroke. Methods. A total of 21 subjects with acute stroke were randomized into 2 groups, FES plus conventional occupational and physiotherapy (FES group) or only conventional therapy (control group) 5 days a week for 12 to 16 weeks. A third group of 7 subjects with chronic hemiplegia (at least 5 months poststroke) received only FES therapy (chronic group) and pre—post training changes were compared. FES was applied to proximal and then distal muscle groups during specific motor tasks. At baseline and at the end of treatment, grasping function was assessed using the Rehabilitation Engineering Laboratory Hand Function Test, along with more standard measures of rehabilitation outcome. Results. The FES group improved significantly more than the control group in terms of object manipulation, palmar grip torque, pinch grip pulling force, Barthel Index, Upper Extremity Fugl—Meyer scores, and Upper Extremity Chedoke—McMaster Stages of Motor Recovery. The chronic stroke subjects demonstrated improvements in most categories, but the changes were not statistically significant. Conclusions. FES therapy with upper extremity training may be an efficacious intervention in the rehabilitation of reaching and grasping function during acute stroke rehabilitation.

Task-Relevant Modulation of Contralateral and Ipsilateral Primary Somatosensory Cortex and the Role of a Prefrontal-Cortical Sensory Gating System

Electrophysiological studies have shown that task-relevant somatosensory information leads to selective facilitation within the primary somatosensory cortex (SI). The purpose of the present study was (1) to further explore the relationship between the relevancy of stimuli and activation within the contralateral and ipsilateral SI and (2) to provide further insight into the specific sensory gating network responsible for modulating neural activity within SI. Functional MRI of 12 normal subjects was performed with vibrotactile stimuli presented to the pad of the index finger. In experiment 1, the stimulus was presented to either the left or the right hand. Subjects were required to detect transient changes in stimulus frequency. In experiment 2, stimuli were presented to either the right hand alone or both hands simultaneously. Stimuli were applied either (A) passively or (B) when subjects were asked to detect frequency changes that occurred to the right hand only. In experiment 1, task-relevant somatosensory stimulation led not only to enhanced contralateral SI activity, but also to a suppression of activity in the ipsilateral SI. In experiment 2, SI activation was enhanced when stimuli were task-relevant, compared to that observed with passive input. When stimuli were presented simultaneously to both hands, only those that were task-relevant increased SI activation. This was associated with recruitment of a network of cortical regions, including the right prefrontal cortex (Brodmann area 9). We conclude that SI modulation is dependent on task relevancy and that this modulation may be regulated, at least in part, by the prefrontal cortex.

The control of lateral stability during rapid stepping reactions evoked by antero-posterior perturbation: does anticipatory control play a role?

Volitional step initiation invariably includes a medio-lateral anticipatory postural adjustment (ML APA), which causes the center of mass (COM) to be propelled toward the stance-limb side prior to the lifting of the swing foot. The present study examined whether this type of anticipatory control plays a functional role in maintaining lateral stability during the rapid compensatory stepping reactions that are evoked when whole-body stability is challenged by unpredictable perturbation. Forward and backward stepping reactions were evaluated in five healthy young adults (ages 22-28) under three task conditions: (1) unconstrained compensatory stepping evoked by platform translation (no specific instructions), (2) constrained compensatory stepping cued by platform translation (prior instruction to step rapidly), and (3) rapid voluntary stepping to a light cue. ML APAs occurred during 70% of perturbation reactions but were too small and brief to have a substantive influence on the lateral movement of the COM occurring during leg lift or swing phase. In contrast, during the light-cued stepping, the ML APA propelled the COM toward the stance-limb side prior to the lifting of the swing limb, and effectively reduced the tendency of the COM to fall toward the swing-limb side during the execution of the step. It is proposed that the presence of an ML APA during compensatory stepping may represent an attempt to preplan a stereotypical stepping response, but that the ability to fully express the anticipatory phase is disrupted by the need to react rapidly to the unpredictable antero-posterior instability imposed by the perturbation. The results suggest that anticipatory control is not the primary mechanism by which the central nervous system deals with the lateral instability arising during rapid compensatory stepping reactions evoked by large, unpredictable antero-posterior perturbation.

Sensorimotor Cortical Plasticity During Recovery Following Spinal Cord Injury: A Longitudinal fMRI Study

Background. Although the consequences of spinal cord injury (SCI) within the spinal cord and peripheral nervous system have been studied extensively, the influence of SCI on supraspinal structures during recovery remains largely unexplored. Objective. To assess temporal changes in cortical sensorimotor representations beginning in the subacute phase following SCI and determine if an association exists between the plastic changes within cortical sensorimotor areas and recovery of movement postinjury. Methods. Functional magnetic resonance imaging (fMRI) was used to study 6 SCI patients for 1 year, beginning shortly postinjury, and 10 healthy control individuals. During fMRI, individuals performed a simple self-paced wrist extension motor task. Recovery of movement was assessed using the American Spinal Injury Association (ASIA) Standard Neurological Classification of SCI. Results. In the subacute period post-SCI, during impaired movement, little task-related activation within the primary motor cortex (M1) was present, whereas activation in associated cortical sensorimotor areas was more extensive than in controls. During motor recovery, a progressive enlargement in the volume of movement-related M1 activation and decreased activation in associated cortical sensorimotor areas was seen. When movement was performed with little to no impairment, the overall pattern of cortical activation was similar to that observed in control individuals. Conclusions . This study provides the first report of the temporal progression of cortical sensorimotor representational plasticity during recovery following traumatic SCI in humans and suggests an association between movement-related fMRI activation and motor recovery postinjury. These findings have implications on current and future rehabilitative interventions for patients with SCI.

Quantifying Head Motion Associated with Motor Tasks Used in fMRI

In functional magnetic resonance imaging (fMRI) studies, long experiment times and small intensity changes associated with brain activation frequently lead to image artifacts due to head motion. Methods to minimize and correct for head motion by restraint, fast imaging, and retrospective image registration are typically combined but do not completely solve the problem, particularly for specific patient populations. As an initial step toward optimizing future designs of head restraints and improving motion correction techniques, the head motion characteristics of groups of stroke subjects, age-matched controls, and young adults were investigated with the aid of an MR simulator and a highly accurate position tracking system. Position measurements were recorded during motor tasks involving either the hand or the foot. Head motion was strongly dependent on the subject group and less upon the task conditions based on ANOVA calculations (P < 0.05). The stroke subjects exhibited approximately twice the head motion compared to that of age-matched controls, and the latters head motion was about twice that of young adults. Moreover, the range of head motion in stroke subjects over all tasks was approximately 2 +/- 1 mm, with the motion occurring predominantly as translation in the superior-inferior direction and pitch rotation (nodding). These results lead to several recommendations on the design of fMRI motor experiments and suggest that improved motion correction strategies are required to examine such patient populations comprehensively.