Assessment of cortical reorganisation for hand function after stroke

Reorganizing therapy: changing the clinical approach to upper limb recovery post-stroke

Stroke is the leading cause of adult disability, and as a consequence, most therapists will provide health care to patients with stroke during their professional careers. An increasing number of studies are investigating the association between upper limb recovery and changes in brain activation patterns following stroke. In this review, we explore the translational implications of this research for health professionals working in stroke recovery. We argue that in light of the most recent evidence, therapists should consider how best to take full advantage of the brain's natural ability to reorganize, when prescribing and applying interventions to those with a stroke-affected upper limb. The authors propose that stroke is a brain-based problem that needs a brain-based solution. This review addresses two topics, anticipating recovery and maximizing recovery. It proposes five practice-ready recommendations that are based on the evidence reviewed. The over-riding aim of this review and discussion is to challenge therapists to reconsider the health care they prescribe and apply to people with a stroke-affected upper limb.

Changes in brain activation in stroke patients after mental practice and physical exercise: a functional MRI study

Mental practice is a new rehabilitation method that refers to the mental rehearsal of motor imagery content with the goal of improving motor performance. However, the relationship between activated regions and motor recovery after mental practice training is not well understood. In this study, 15 patients who suffered a first-ever subcortical stroke with neurological deficits affecting the right hand, but no significant cognitive impairment were recruited. 10 patients underwent mental practice combined with physical practice training, and 5 patients only underwent physical practice training. We observed brain activation regions after 4 weeks of training, and explored the correlation of activation changes with functional recovery of the affected hands. The results showed that, after 4 weeks of mental practice combined with physical training, the Fugl-Meyer assessment score for the affected right hand was significantly increased than that after 4 weeks of practice training alone. Functional MRI showed enhanced activation in the left primary somatosensory cortex, attenuated activation intensity in the right primary motor cortex, and enhanced right cerebellar activation observed during the motor imagery task using the affected right hand after mental practice training. The changes in brain cortical activity were related to functional recovery of the hand. Experimental findings indicate that cortical and cerebellar functional reorganization following mental practice contributed to the improvement of hand function.

Do movement-related beta oscillations change after stroke?

Stroke is the most common cause of physical disability in the world today. While the key element of rehabilitative therapy is training, there is currently much interest in approaches that “prime” the primary motor cortex to be more excitable, thereby increasing the likelihood of experience-dependent plasticity. Cortical oscillations reflect the balance of excitation and inhibition, itself a key determinant of the potential for experience-dependent plasticity. In the motor system, beta-band oscillations are important and are thought to maintain the resting sensorimotor state. Here we examined motor cortex beta oscillations during rest and unimanual movement in a group of stroke patients and healthy control subjects, using magnetoencephalography. Movement-related beta desynchronization (MRBD) in contralateral primary motor cortex was found to be significantly reduced in patients compared with control subjects. Within the patient group, smaller MRBD was seen in those with more motor impairment. We speculate that impaired modulation of beta oscillations during affected hand grip is detrimental to motor control, highlighting this as a potential therapeutic target in neurorehabilitation.

Multimodal sensory feedback associated with motor attempts alters BOLD responses to paralyzed hand movement in chronic stroke patients

Electroencephalogram-based brain-computer interfaces (BCI) have been used as a potential tool for training volitional regulation of corticomuscular drive in patients who have severe hemiplegia due to stroke. However, it is unclear whether ERD observed while attempting motor execution can be regarded as a neural marker that represents M1 excitability in survivors of severe stroke. Therefore we investigated the association between ERD and the blood-oxygen-level-dependent (BOLD) fMRI signal during attempted movement of a paralyzed finger in stroke patients. Nine chronic stroke patients received BCI training for finger extension movement 1 h daily for a duration of 1 month. The sensorimotor rhythm was recorded from the sensorimotor area of the damaged hemisphere, and ongoing amplitude variations were monitored using a BCI system. Either a visual alert or the action of a motor-driven orthosis was triggered in response to ERD of the sensorimotor rhythm while patients attempted extension movements of the paralyzed fingers. Inter-subject covariance between ERD and the BOLD response in the sensorimotor areas was calculated. After BCI training, an increased ERD over the damaged hemisphere was confirmed in all participants while they attempted extension of the affected finger and this increase was associated with a BOLD response in primary sensorimotor area. Whole-brain MRI revealed that the primary sensorimotor area and supplementary motor area were activated in the damaged hemisphere after 1 month of BCI training. ERD reflects the BOLD responses of the primary motor areas in either hemisphere while patients who have severe chronic hemiplegia due to a stroke attempt an extension movement of the paralyzed fingers. One month of BCI can alter motor-related brain area activation. Combining BCI with other methods to facilitate such changes may help to implement BCI for motor rehabilitation after stroke.

Predictors and biomarkers of treatment gains in a clinical stroke trial targeting the lower extremity

BACKGROUND AND PURPOSE

Behavioral measures are often used to distinguish subgroups of patients with stroke (eg, to predict treatment gains, stratify clinical trial enrollees, or select rehabilitation therapy). In studies of the upper extremity, measures of brain function using functional magnetic resonance imaging (fMRI) have also been found useful, but this approach has not been examined for the lower extremity. The current study hypothesized that an fMRI-based measure of cortical function would significantly improve prediction of treatment-induced lower extremity behavioral gains. Biomarkers of treatment gains were also explored.

METHODS

Patients with hemiparesis 1 to 12 months after stroke were enrolled in a double-blind, placebo-controlled, randomized clinical trial of ropinirole+physical therapy versus placebo+physical therapy, results of which have previously been reported (NCT00221390).(15) Primary end point was change in gait velocity. Enrollees underwent baseline multimodal assessment that included 19 measures spanning 5 assessment categories (medical history, impairment, disability, brain injury, and brain function), and also underwent reassessment 3 weeks after end of therapy.

RESULTS

In bivariate analysis, 8 baseline measures belonging to 4 categories (medical history, impairment, disability, and brain function) significantly predicted change in gait velocity. Prediction was strongest, however, using a multivariate model containing 2 measures (leg Fugl-Meyer score and fMRI activation volume within ipsilesional foot sensorimotor cortex). Increased activation volume within bilateral foot primary sensorimotor cortex correlated positively with treatment-induced leg motor gains.

CONCLUSIONS

A multimodal model incorporating behavioral and fMRI measures best predicted treatment-induced changes in gait velocity in a clinical trial setting. Results also suggest potential use of fMRI measures as biomarkers of treatment gains.

Upper limb recovery after stroke is associated with ipsilesional primary motor cortical activity: a meta-analysis

BACKGROUND AND PURPOSE

Although neuroimaging studies have revealed specific patterns of reorganization in the sensorimotor control network after stroke, their role in recovery remains unsettled. To review the existing evidence systematically, we performed activation likelihood estimation meta-analysis of functional neuroimaging studies investigating upper limb movement-related brain activity after stroke.

METHODS

Twenty-four studies using sensorimotor tasks in standardized coordinates were included, totaling 255 patients and 145 healthy controls. Across the entire brain, we compared task-related activity patterns in good and poor recovery and assessed the magnitude of spatial shifts in sensorimotor activity in cortical motor areas after stroke.

RESULTS

When compared with healthy controls, patients showed higher activation likelihood estimation values in contralesional primary motor soon after stroke that abated with time, but were not related to motor outcome. The observed activity changes were consistent with restoration of typical interhemispheric balance. In contrast, activation likelihood estimation values in ipsilesional medial-premotor and primary motor cortex were associated with good outcome, reorganization that may reflect vicarious processes associated with ventral activity shifts from BA4a to 4p. In the anterior cerebellum, a novel finding was the association of poor recovery with increased vermal activity, possibly reflecting behaviorally inadequate compensatory strategies engaging the fastigio-thalamo-cortical and corticoreticulospinal systems.

CONCLUSIONS

Activity in ipsilesional primary motor and medial-premotor cortices in chronic stroke signals good motor recovery, whereas cerebellar vermis activity signals poor recovery. Functional MRI may be useful in identifying recovery biomarkers.

Cortical reorganization after stroke: how much and how functional?

The brain has an intrinsic capacity to compensate for structural damage through reorganizing of surviving networks. These processes are fundamental for recovery of function after many forms of brain injury, including stroke. Functional neuroimaging techniques have allowed the investigation of these processes in vivo. Here, we review key advances over the past two decades that have shed light on the neural mechanisms enabling recovery of motor function after stroke. We first provide an overview on invasive stroke models in non-human primates that provided insights into lesion-induced changes in the cortical representations of the upper limb. We then present key findings from neuroimaging studies in human stroke patients, which suggest that the role of contralesional motor hemisphere in supporting recovered function depends on factors such as time since stroke, lesion location and anatomical region. More recently, research has been directed at understanding how surviving brain regions influence one another during movement. It appears that it is not only the corticospinal tract but also brainstem pathways and interhemispheric connections that affect cortical reorganization patterns and functional recovery. In summary, neuroimaging opens the way for greater understanding of the mechanisms of recovery and potentially improves our ability to deliver effective restorative therapy.

Rehabilitation with poststroke motor recovery: a review with a focus on neural plasticity

Motor recovery after stroke is related to neural plasticity, which involves developing new neuronal interconnections, acquiring new functions, and compensating for impairment. However, neural plasticity is impaired in the stroke-affected hemisphere. Therefore, it is important that motor recovery therapies facilitate neural plasticity to compensate for functional loss. Stroke rehabilitation programs should include meaningful, repetitive, intensive, and task-specific movement training in an enriched environment to promote neural plasticity and motor recovery. Various novel stroke rehabilitation techniques for motor recovery have been developed based on basic science and clinical studies of neural plasticity. However, the effectiveness of rehabilitative interventions among patients with stroke varies widely because the mechanisms underlying motor recovery are heterogeneous. Neurophysiological and neuroimaging studies have been developed to evaluate the heterogeneity of mechanisms underlying motor recovery for effective rehabilitation interventions after stroke. Here, we review novel stroke rehabilitation techniques associated with neural plasticity and discuss individualized strategies to identify appropriate therapeutic goals, prevent maladaptive plasticity, and maximize functional gain in patients with stroke.

Noninvasive brain stimulation in neurorehabilitation

Stroke is the major cause of long-term disability worldwide, with impaired manual dexterity being a common feature. In the past few years, noninvasive brain stimulation (NIBS) techniques, such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have been investigated as adjuvant strategies to neurorehabilitative interventions. These NIBS techniques can be used to modulate cortical excitability during and for several minutes after the end of the stimulation period. Depending on the stimulation parameters, cortical excitability can be reduced (inhibition) or enhanced (facilitation). Differential modulation of cortical excitability in the affected and unaffected hemisphere of patients with stroke may induce plastic changes within neural networks active during functional recovery. The aims of this chapter are to describe results from these proof-of-principle trials and discuss possible putative mechanisms underlying such effects. Neurophysiological and neuroimaging changes induced by application of NIBS are reviewed briefly.

How does brain activation differ in children with unilateral cerebral palsy compared to typically developing children, during active and passive movements, and tactile stimulation? An fMRI study

The aim of the functional magnetic resonance imaging (fMRI) study was to investigate brain activation associated with active and passive movements, and tactile stimulation in 17 children with right-sided unilateral cerebral palsy (CP), compared to 19 typically developing children (TD). The active movements consisted of repetitive opening and closing of the hand. For passive movements, an MRI-compatible robot moved the finger up and down. Tactile stimulation was provided by manually stroking the dorsal surface of the hand with a sponge cotton cloth. In both groups, contralateral primary sensorimotor cortex activation (SM1) was seen for all tasks, as well as additional contralateral primary somatosensory cortex (S1) activation for passive movements. Ipsilateral cerebellar activity was observed in TD children during all tasks, but only during active movements in CP children. Of interest was additional ipsilateral SM1 recruitment in CP during active movements as well as ipsilateral S1 activation during passive movements and tactile stimulation. Another interesting new finding was the contralateral cerebellum activation in both groups during different tasks, also in cerebellar areas not primarily linked to the sensorimotor network. Active movements elicited significantly more brain activation in CP compared to TD children. In both groups, active movements displayed significantly more brain activation compared to passive movements and tactile stimulation.

What is the nature of poststroke language recovery and reorganization?

This review focuses on three main topics related to the nature of poststroke language recovery and reorganization. The first topic pertains to the nature of anatomical and physiological substrates in the infarcted hemisphere in poststroke aphasia, including the nature of the hemodynamic response in patients with poststroke aphasia, the nature of the peri-infarct tissue, and the neuronal plasticity potential in the infarcted hemisphere. The second section of the paper reviews the current neuroimaging evidence for language recovery in the acute, subacute, and chronic stages of recovery. The third and final section examines changes in connectivity as a function of recovery in poststroke aphasia, specifically in terms of changes in white matter connectivity, changes in functional effective connectivity, and changes in resting state connectivity after stroke. While much progress has been made in our understanding of language recovery, more work needs to be done. Future studies will need to examine whether reorganization of language in poststroke aphasia corresponds to a tighter, more coherent, and efficient network of residual and new regions in the brain. Answering these questions will go a long way towards being able to predict which patients are likely to recover and may benefit from future rehabilitation.

European Stroke Science Workshop

The European Stroke Organisation held its first European Stroke Science Workshop in Garmisch-Partenkirchen, Germany (December 15-17, 2011). Stroke experts based in Europe were invited to present and discuss their current research. The scope of the workshop was to review the most recent findings of selected topics in stroke, to exchange ideas, to stimulate new research, and to enhance collaboration between European stroke research groups. Seven scientific sessions were held, each starting with a keynote lecture to review the state of the art of the given topic, followed by 4 or 5 short presentations by experts. They were asked to limit their presentations to 10 slides containing only recent information. The meeting was organized by the executive committee of the European Stroke Organisation (Heinrich Mattle, chairman, Michael Brainin, Angel Chamorro, Werner Hacke, Didier Leys) and supported by the European Stroke Conference (Michael Hennerici). The following sections summarize the content of the workshop.

European stroke science workshop

The European Stroke Organisation held its first European Stroke Science Workshop in Garmisch-Partenkirchen, Germany (December 15-17, 2011). Stroke experts based in Europe were invited to present and discuss their current research. The scope of the workshop was to review the most recent findings of selected topics in stroke, to exchange ideas, to stimulate new research, and to enhance collaboration between European stroke research groups. Seven scientific sessions were held, each starting with a keynote lecture to review the state of the art of the given topic, followed by 4 or 5 short presentations by experts. They were asked to limit their presentations to 10 slides containing only recent information. The meeting was organized by the executive committee of the European Stroke Organisation (Heinrich Mattle, chairman, Michael Brainin, Angel Chamorro, Werner Hacke, Didier Leys) and supported by the European Stroke Conference (Michael Hennerici). The following sections summarize the content of the workshop.

The PREP algorithm predicts potential for upper limb recovery after stroke

Stroke is a leading cause of adult disability and the recovery of motor function is important for independence in activities of daily living. Predicting motor recovery after stroke in individual patients is difficult. Accurate prognosis would enable realistic rehabilitation goal-setting and more efficient allocation of resources. The aim of this study was to test and refine an algorithm for predicting the potential for recovery of upper limb function after stroke. Forty participants were prospectively enrolled within 3 days of ischaemic stroke. First, shoulder abduction and finger extension strength were graded 72 h after stroke onset to compute a shoulder abduction and finger extension score. Secondly, transcranial magnetic stimulation was used to assess the functional integrity of descending motor pathways to the affected upper limb. Third, diffusion-weighted magnetic resonance imaging was used to assess the structural integrity of the posterior limbs of the internal capsules. Finally, these measures were combined in the PREP algorithm for predicting an individual's potential for upper limb recovery at 12 weeks, measured with the Action Research Arm Test. A cluster analysis was used to independently group patients according to Action Research Arm Test score at 12 weeks, for comparison with predictions from the PREP algorithm. There was excellent correspondence between the cluster analysis of Action Research Arm Test score at 12 weeks and predictions made with the PREP algorithm. The algorithm had positive predictive power of 88%, negative predictive power of 83%, specificity of 88% and sensitivity of 73%. This study provides preliminary data in support of the PREP algorithm for the prognosis of upper limb recovery in individual patients. PREP may enable tailored planning of rehabilitation and more accurate stratification of patients in clinical trials.

Constraints for control of the human hand

More than 30 muscles drive the hand to perform a multitude of essential dextrous tasks. Here we consider new views on the evolution of hand structure and on peripheral and central constraints for independent control of the digits of the hand. The human hand is widely assumed to have evolved from hands like those of African apes, yet recent studies have shown that our hands and those of the earliest hominids are very similar and unlike those of living apes. Understanding the limits of hand function may come from investigation of our last common ancestor with the great apes, rather than the great apes themselves. In the periphery, movement across the full range of joint space can be limited by mechanical linkages among the extrinsic muscles. Further, peripheral limits occur when the hand adopts some positions in which the contraction of muscles fails to move the joints on which they usually act; there is muscle 'disengagement' and functional paralysis for some actions. Surprisingly, the central nervous system drives the hand seamlessly through this landscape of mechanical limits. Central constraints on control of the individual digits include the spillover of neural drive to neighbouring muscles and their 'compartments', and the inability to make maximal muscle forces when multiple digits contract strongly which produces a force deficit. The pattern of these latter constraints correlates with amounts of daily use of each digit and favours enslaved extension to lift fingers from an object but selective flexion of fingers to contact it.

The primate reticulospinal tract, hand function and functional recovery

Abstract

The primate reticulospinal tract is usually considered to control proximal and axial muscles, and to be involved mainly in gross movements such as locomotion, reaching and posture. This contrasts with the corticospinal tract, which is thought to be involved in fine control, particularly of independent finger movements. Recent data provide evidence that the reticulospinal tract can exert some influence over hand movements. Although clearly secondary to the corticospinal tract in healthy function, this could assume considerable importance after corticospinal lesion (such as following stroke), when reticulospinal systems could provide a substrate for some recovery of function. We need to understand more about the abilities of the reticular formation to process sensory input and guide motor output, so that rehabilitation strategies can be optimised to work with the innate capabilities of reticular motor control.