A pilot study of event-related functional magnetic resonance imaging of monitored wrist movements in patients with partial recovery

Functional magnetic resonance imaging in chronic ischaemic stroke

Ischaemic stroke is the leading cause of adult disability worldwide. Effective rehabilitation is hindered by uncertainty surrounding the underlying mechanisms that govern long-term ischaemic injury progression. Despite its potential as a sensitive non-invasive in vivo marker of brain function that may aid in the development of new treatments, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has found limited application in the clinical research on chronic stage stroke progression. Stroke affects each of the physiological parameters underlying the BOLD contrast, markedly complicating the interpretation of BOLD fMRI data. This review summarizes current progress on application of BOLD fMRI in the chronic stage of ischaemic injury progression and discusses means by which more information may be gained from such BOLD fMRI measurements. Concomitant measurements of vascular reactivity, neuronal activity and metabolism in preclinical models of stroke are reviewed along with illustrative examples of post-ischaemic evolution in neuronal, glial and vascular function. The realization of the BOLD fMRI potential to propel stroke research is predicated on the carefully designed preclinical research establishing an ischaemia-specific quantitative model of BOLD signal contrast to provide the framework for interpretation of fMRI findings in clinical populations.This article is part of the themed issue 'Interpreting BOLD: a dialogue between cognitive and cellular neuroscience'.

Topographical measures of functional connectivity as biomarkers for post-stroke motor recovery

BACKGROUND

Biomarkers derived from neural activity of the brain present a vital tool for the prediction and evaluation of post-stroke motor recovery, as well as for real-time biofeedback opportunities.

METHODS

In order to encapsulate recovery-related reorganization of brain networks into such biomarkers, we have utilized the generalized measure of association (GMA) and graph analyses, which include global and local efficiency, as well as hemispheric interdensity and intradensity. These methods were applied to electroencephalogram (EEG) data recorded during a study of 30 stroke survivors (21 male, mean age 57.9 years, mean stroke duration 22.4 months) undergoing 12 weeks of intensive therapeutic intervention.

RESULTS

We observed that decreases of the intradensity of the unaffected hemisphere are correlated (r s =-0.46;p<0.05) with functional recovery, as measured by the upper-extremity portion of the Fugl-Meyer Assessment (FMUE). In addition, high initial values of local efficiency predict greater improvement in FMUE (R 2=0.16;p<0.05). In a subset of 17 subjects possessing lesions of the cerebral cortex, reductions of global and local efficiency, as well as the intradensity of the unaffected hemisphere are found to be associated with functional improvement (r s =-0.60,-0.66,-0.75;p<0.05). Within the same subgroup, high initial values of global and local efficiency, are predictive of improved recovery (R 2=0.24,0.25;p<0.05). All significant findings were specific to the 12.5-25 Hz band.

CONCLUSIONS

These topological measures show promise for prognosis and evaluation of therapeutic outcomes, as well as potential application to BCI-enabled biofeedback.

Functional Neuroimaging in Stroke Recovery and Neurorehabilitation: Conceptual Issues and Perspectives

Background

In stroke, functional neuroimaging has become a potent diagnostic tool; opened new insights into the pathophysiology of ischaemic damage in the human brain; and made possible the assessment of functional–structural relationships in postlesion recovery.

Summary of review

Here, we give a critical account on the potential and limitation of functional neuroimaging and discuss concepts related to the use of neuroimaging for exploring the neurobiological and neuroanatomical mechanisms of poststroke recovery and neurorehabilitation. We identify and provide evidence for five hypotheses that functional neuroimaging can provide new insights into: adaptation occurs at the level of functional brain systems; the brain–behaviour relationship varies with recovery and over time; functional neuroimaging can improve our ability to predict recovery and select individuals for rehabilitation; mechanisms of recovery reflect different pathophysiological phases; and brain adaptation may be modulated by experience and specific rehabilitation. The significance and application of this new evidence is discussed, and recommendations made for investigations in the field.

Conclusion

Functional neuroimaging is an important tool to explore the mechanisms underlying brain plasticity and, thereby, to guide clinical research in neurorehabilitation.

A novel fMRI paradigm suggests that pedaling-related brain activation is altered after stroke

The purpose of this study was to examine the feasibility of using functional magnetic resonance imaging (fMRI) to measure pedaling-related brain activation in individuals with stroke and age-matched controls. We also sought to identify stroke-related changes in brain activation associated with pedaling. Fourteen stroke and 12 control subjects were asked to pedal a custom, MRI-compatible device during fMRI. Subjects also performed lower limb tapping to localize brain regions involved in lower limb movement. All stroke and control subjects were able to pedal while positioned for fMRI. Two control subjects were withdrawn due to claustrophobia, and one control data set was excluded from analysis due to an incidental finding. In the stroke group, one subject was unable to enter the gantry due to excess adiposity, and one stroke data set was excluded from analysis due to excessive head motion. Consequently, 81% of subjects (12/14 stroke, 9/12 control) completed all procedures and provided valid pedaling-related fMRI data. In these subjects, head motion was ≤3 mm. In both groups, brain activation localized to the medial aspect of M1, S1, and Brodmann's area 6 (BA6) and to the cerebellum (vermis, lobules IV, V, VIII). The location of brain activation was consistent with leg areas. Pedaling-related brain activation was apparent on both sides of the brain, with values for laterality index (LI) of -0.06 (0.20) in the stroke cortex, 0.05 (±0.06) in the control cortex, 0.29 (0.33) in the stroke cerebellum, and 0.04 (0.15) in the control cerebellum. In the stroke group, activation in the cerebellum - but not cortex - was significantly lateralized toward the damaged side of the brain (p = 0.01). The volume of pedaling-related brain activation was smaller in stroke as compared to control subjects. Differences reached statistical significance when all active regions were examined together [p = 0.03; 27,694 (9,608) μL stroke; 37,819 (9,169) μL control]. When individual regions were examined separately, reduced brain activation volume reached statistical significance in BA6 [p = 0.04; 4,350 (2,347) μL stroke; 6,938 (3,134) μL control] and cerebellum [p = 0.001; 4,591 (1,757) μL stroke; 8,381 (2,835) μL control]. Regardless of whether activated regions were examined together or separately, there were no significant between-group differences in brain activation intensity [p = 0.17; 1.30 (0.25)% stroke; 1.16 (0.20)% control]. Reduced volume in the stroke group was not observed during lower limb tapping and could not be fully attributed to differences in head motion or movement rate. There was a tendency for pedaling-related brain activation volume to increase with increasing work performed by the paretic limb during pedaling (p = 0.08, r = 0.525). Hence, the results of this study provide two original and important contributions. First, we demonstrated that pedaling can be used with fMRI to examine brain activation associated with lower limb movement in people with stroke. Unlike previous lower limb movements examined with fMRI, pedaling involves continuous, reciprocal, multijoint movement of both limbs. In this respect, pedaling has many characteristics of functional lower limb movements, such as walking. Thus, the importance of our contribution lies in the establishment of a novel paradigm that can be used to understand how the brain adapts to stroke to produce functional lower limb movements. Second, preliminary observations suggest that brain activation volume is reduced during pedaling post-stroke. Reduced brain activation volume may be due to anatomic, physiology, and/or behavioral differences between groups, but methodological issues cannot be excluded. Importantly, brain action volume post-stroke was both task-dependent and mutable, which suggests that it could be modified through rehabilitation. Future work will explore these possibilities.

Functional Neuroimaging in Motor Recovery After Stroke

Neuroimaging techniques provide information on the neural substrates underlying functional recovery after stroke, the number one cause of long-term disability. Despite the methodological difficulties, they promise to offer insight into the mechanisms by which therapeutic interventions can modulate human cortical plasticity. This information should lead to the development of new, targeted interventions to maximize recovery.

Mirror illusion reduces motor cortical inhibition in the ipsilateral primary motor cortex during forceful unilateral muscle contractions

Forceful, unilateral contractions modulate corticomotor paths targeting the resting, contralateral hand. However, it is unknown whether mirror-viewing of a slowly moving but forcefully contracting hand would additionally affect these paths. Here we examined corticospinal excitability and short-interval intracortical inhibition (SICI) of the right-ipsilateral primary motor cortex (M1) in healthy young adults under no-mirror and mirror conditions at rest and during right wrist flexion at 60% maximal voluntary contraction (MVC). During the no-mirror conditions neither hand was visible, whereas in the mirror conditions participants looked at the right hand's reflection in the mirror. Corticospinal excitability increased during contractions in the left flexor carpi radialis (FCR) (contraction 0.41 mV vs. rest 0.21 mV) and extensor carpi radialis (ECR) (contraction 0.56 mV vs. rest 0.39 mV), but there was no mirror effect (FCR: P = 0.743, ηp (2) = 0.005; ECR: P = 0.712, ηp (2) = 0.005). However, mirror-viewing of the contracting and moving wrist attenuated SICI relative to test pulse in the left FCR by ∼9% compared with the other conditions (P < 0.05, d ≥ 0.62). Electromyographic activity in the resting left hand prior to stimulation was not affected by the mirror (FCR: P = 0.255, ηp (2) = 0.049; ECR: P = 0.343, ηp (2) = 0.035) but increased twofold during contractions. Thus viewing the moving hand in the mirror and not just the mirror image of the nonmoving hand seems to affect motor cortical inhibitory networks in the M1 associated with the mirror image. Future studies should determine whether the use of a mirror could increase interlimb transfer produced by cross-education, especially in patient groups with unilateral orthopedic and neurological conditions.

Beyond BOLD: optimizing functional imaging in stroke populations

Blood oxygenation level-dependent (BOLD) signal changes are often assumed to directly reflect neural activity changes. Yet the real relationship is indirect, reliant on numerous assumptions, and subject to several sources of noise. Deviations from the core assumptions of BOLD contrast functional magnetic resonance imaging (fMRI), and their implications, have been well characterized in healthy populations, but are frequently neglected in stroke populations. In addition to conspicuous local structural and vascular changes after stroke, there are many less obvious challenges in the imaging of stroke populations. Perilesional ischemic changes, remodeling in regions distant to lesion sites, and diffuse perfusion changes all complicate interpretation of BOLD signal changes in standard fMRI protocols. Most stroke patients are also older than the young populations on which assumptions of neurovascular coupling and the typical analysis pipelines are based. We present a review of the evidence to show that the basic assumption of neurovascular coupling on which BOLD-fMRI relies does not capture the complex changes arising from stroke, both pathological and recovery related. As a result, estimating neural activity using the canonical hemodynamic response function is inappropriate in a number of contexts. We review methods designed to better estimate neural activity in stroke populations. One promising alternative to event-related fMRI is a resting-state-derived functional connectivity approach. Resting-state fMRI is well suited to stroke populations because it makes no performance demands on patients and is capable of revealing network-based pathology beyond the lesion site.

Role of the mirror-neuron system in cross-education

The present review proposes the untested hypothesis that cross-education performed with a mirror increases the transfer of motor function to the resting limb compared with standard cross-education interventions without a mirror. The hypothesis is based on neuroanatomical evidence suggesting an overlap in activated brain areas when a unilateral motor task is performed with and without a mirror in the context of cross-education of the upper extremities. The review shows that the mirror-neuron system (MNS), connecting sensory neurons responding to visual properties of an observed action and motor neurons that discharge action potentials during the execution of a similar action, has the potential to enhance cross-education.

Response of gait deficits to neuromuscular electrical stimulation for stroke survivors

Persistent gait deficits after stroke can cause falls, elevated energy cost and poor endurance. Coordination impairment is an underlying cause of gait deficits. Few efficacious interventions have been described that have targeted and measured restoration of coordinated gait components. Neuromuscular electrical stimulation can provide the critical gait practice characteristic of close-to-normal movements, by electrically inducing muscle contractions and coordinated movements that are not possible under volitional effort. Two-channel, surface neuromuscular electrical stimulation can be synchronized with phases of gait and can provide faster, more symmetrical neuromuscular electrical stimulation-assisted gait than gait with no neuromuscular electrical stimulation. Difficulties encountered during the use of surface neuromuscular electrical stimulation for gait training led to the development of neuromuscular electrical stimulation with implanted technologies. Implanted electrodes and/or stimulators proved to be feasible for gait training in stroke survivors. Gait training with a multichannel neuromuscular electrical stimulation system with implanted electrodes proved more advantageous than gait training without neuromuscular electrical stimulation, according to measures of volitional coordinated gait components (neuromuscular electrical stimulation deactivated).

Changes in hemodynamic responses in chronic stroke survivors do not affect fMRI signal detection in a block experimental design

The use of canonical functions to model BOLD-fMRI data in people post-stroke may lead to inaccurate descriptions of task-related brain activity. The purpose of this study was to determine whether the spatiotemporal profile of hemodynamic responses (HDRs) obtained from stroke survivors during an event-related experiment could be used to develop individualized HDR functions that would enhance BOLD-fMRI signal detection in block experiments. Our long term goal was to use this information to develop individualized HDR functions for stroke survivors that could be used to analyze brain activity associated with locomotor-like movements. We also aimed to examine the reproducibility of HDRs obtained across two scan sessions in order to determine whether data from a single event-related session could be used to analyze block data obtained in subsequent sessions. Results indicate that the spatiotemporal profile of HDRs measured with BOLD-fMRI in stroke survivors was not the same as that observed in individuals without stroke. We observed small between-group differences in the rates of rise and decline of HDRs that were more apparent in individuals with cortical as compared to subcortical stroke. There were no differences in the peak or time to peak of HDRs in people with and without stroke. Of interest, differences in HDRs were not as substantial as expected from previous reports and were not large enough to necessitate the use of individualized HDR functions to obtain valid measures of movement-related brain activity. We conclude that all strokes do not affect the spatiotemporal characteristics of HDRs in such a way as to produce inaccurate representations of brain activity as measured by BOLD-fMRI. However, care should be taken to identify individuals whose BOLD-fMRI data may not provide an accurate representation of underlying brain activation when canonical models are used. Examination of HDRs need not be done for each scan session, as our data suggest that the characteristics of HDRs in stroke survivors are reproducible across days.

Visualization of altered neurovascular coupling in chronic stroke patients using multimodal functional MRI

Evaluation of cortical reorganization in chronic stroke patients requires methods to accurately localize regions of neuronal activity. Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is frequently employed; however, BOLD contrast depends on specific coupling relationships between the cerebral metabolic rate of oxygen (CMRO(2)), cerebral blood flow (CBF), and volume (CBV), which may not exist following stroke. The aim of this study was to understand whether CBF-weighted (CBFw) and CBV-weighted (CBVw) fMRI could be used in sequence with BOLD to characterize neurovascular coupling mechanisms poststroke. Chronic stroke patients (n=11) with motor impairment and age-matched controls (n=11) performed four sets of unilateral motor tasks (60 seconds/30 seconds off/on) during CBFw, CBVw, and BOLD fMRI acquisition. While control participants elicited mean BOLD, CBFw, and CBVw responses in motor cortex (P<0.01), patients showed only mean changes in CBF (P<0.01) and CBV (P<0.01), but absent mean BOLD responses (P=0.20). BOLD intersubject variability was consistent with differing coupling indices between CBF, CBV, and CMRO(2). Thus, CBFw and/or CBVw fMRI may provide crucial information not apparent from BOLD in these patients. A table is provided outlining distinct vascular and metabolic uncoupling possibilities that elicit different BOLD responses, and the strengths and limitations of the multimodal protocol are summarized.

Reorganization of brain function during force production after stroke: a systematic review of the literature

BACKGROUND AND PURPOSE

Damage to motor areas of the brain caused by stroke can produce devastating motor deficits, including aberrant control of force. Reorganization of brain function is a fundamental mechanism involved in recovery of motor control after stroke, and recent advances in neuroimaging have enabled study of this reorganization. This review focuses on neuroimaging studies that have examined reorganization of brain function during force production and force modulation after stroke.

METHODS

The type and extent of reorganization after stroke were characterized by three factors: severity of injury, time after stroke, and impact of therapeutic interventions on brain activation during force production. Twenty-six studies meeting the inclusion criteria could be identified in MEDLINE (1980-2007).

RESULTS

Relevant characteristics of studies (lesion location, chronicity of stroke, and motor task) and mapping techniques varied. During force production, increased activation in secondary motor areas occurred in persons with more severe strokes. Reduced recruitment of secondary motor areas during force production was found as a function of increased time since stroke. During force modulation, increased activation in motor areas occurred with greater force generation. Persons with more severe stroke showed greater activation with increasing force compared with persons with less severe stroke. Alteration of brain activation during and after rehabilitative interventions was identified in some studies.

DISCUSSION AND CONCLUSION

This systematic review establishes that reorganization of brain function during force production and force modulation can occur after stroke. These findings imply that therapeutic strategies may target brain reorganization to improve force control and functional recovery after stroke.

Brain-computer interfaces in neurological rehabilitation

Recent advances in analysis of brain signals, training patients to control these signals, and improved computing capabilities have enabled people with severe motor disabilities to use their brain signals for communication and control of objects in their environment, thereby bypassing their impaired neuromuscular system. Non-invasive, electroencephalogram (EEG)-based brain-computer interface (BCI) technologies can be used to control a computer cursor or a limb orthosis, for word processing and accessing the internet, and for other functions such as environmental control or entertainment. By re-establishing some independence, BCI technologies can substantially improve the lives of people with devastating neurological disorders such as advanced amyotrophic lateral sclerosis. BCI technology might also restore more effective motor control to people after stroke or other traumatic brain disorders by helping to guide activity-dependent brain plasticity by use of EEG brain signals to indicate to the patient the current state of brain activity and to enable the user to subsequently lower abnormal activity. Alternatively, by use of brain signals to supplement impaired muscle control, BCIs might increase the efficacy of a rehabilitation protocol and thus improve muscle control for the patient.

Electrodermal recording and fMRI to inform sensorimotor recovery in stroke patients

BACKGROUND

Functional magnetic resonance imaging (fMRI) appears to be useful for investigating motor recovery after stroke. Some of the potential confounders of brain activation studies, however, could be mitigated through complementary physiological monitoring.

OBJECTIVE

To investigate a sensorimotor fMRI battery that included simultaneous measurement of electrodermal activity in subjects with hemiparetic stroke to provide a measure related to the sense of effort during motor performance.

METHODS

Bilateral hand and ankle tasks were performed by 6 patients with stroke (2 subacute, 4 chronic) during imaging with blood oxygen level-dependent (BOLD) fMRI using an event-related design. BOLD percent changes, peak activation, and laterality index values were calculated in the sensorimotor cortex. Electrodermal recordings were made concurrently and used as a regressor.

RESULTS

Sensorimotor BOLD time series and percent change values provided evidence of an intact motor network in each of these well-recovered patients. During tasks involving the hemiparetic limb, electrodermal activity changes were variable in amplitude, and electrodermal activity time-series data showed significant correlations with fMRI in 3 of 6 patients. No such correlations were observed for control tasks involving the unaffected lower limb.

CONCLUSIONS

Electrodermal activity activation maps implicated the contralesional over the ipsilesional hemisphere, supporting the notion that stroke patients may require higher order motor processing to perform simple tasks. Electrodermal activity recordings may be useful as a physiological marker of differences in effort required during movements of a subject's hemiparetic compared with the unaffected limb during fMRI studies.

Assessment of brain interactivity in the motor cortex from the concept of functional connectivity and spectral analysis of fMRI data

Functional magnetic resonance imaging (fMRI) was used to assess the contributions of movement preparation and execution of a visuomotor task in a cerebral motor network. The functional connectivity of the voxel time series between brain regions in the frequency space was investigated by performing spectral analysis of fMRI time series. The regional interactivities between the two portions of the supplementary motor area (pre-SMA and SMA-proper) and the primary motor cortex (M1), defined as a seed region, were evaluated. The spectral parameter of coherence was used to describe a correlation structure in the frequency domain between two voxel-based time series and to infer the strength of the functional interaction within our presumed motor network of connections. The results showed meaningful differences of the functional interactions between the two portions of the SMA and the M1 area depending on the task conditions. This approach demonstrated the existence of a functional dissociation between the pre-SMA and SMA-proper subregions. We therefore conclude that spectral analysis is useful for identifying functional interactions of brain regions and might provide a powerful tool to quantify changes in connectivity profiles associated with various components of an experimental task.

Movement-dependent stroke recovery: a systematic review and meta-analysis of TMS and fMRI evidence

Evidence indicates that experience-dependent cortical plasticity underlies post-stroke motor recovery of the impaired upper extremity. Motor skill learning in neurologically intact individuals is thought to involve the primary motor cortex, and the majority of studies in the animal literature have studied changes in the primary sensorimotor cortex with motor rehabilitation. Whether changes in engagement in the sensorimotor cortex occur in humans after stroke currently is an area of much interest. The present study conducted a meta-analysis on stroke studies examining changes in neural representations following therapy specifically targeting the upper extremity to determine if rehabilitation-related motor recovery is associated with neural plasticity in the sensorimotor cortex of the lesioned hemisphere. Twenty-eight studies investigating upper extremity neural representations (e.g., TMS, fMRI, PET, or SPECT) were identified, and 13 met inclusion criteria as upper extremity intervention training studies. Common outcome variables representing changes in the primary motor and sensorimotor cortices were used in calculating standardized effect sizes for each study. The primary fixed effects model meta-analysis revealed a large overall effect size (ES=0.84, S.D.=0.15, 95% CI=0.76-0.93). Moreover, a fail-safe analysis indicated that 42 null effect studies would be necessary to lower the overall effect size to an insignificant level. These results indicate that neural changes in the sensorimotor cortex of the lesioned hemisphere accompany functional paretic upper extremity motor gains achieved with targeted rehabilitation interventions.

The relationship between brain activity and peak grip force is modulated by corticospinal system integrity after subcortical stroke

In healthy human subjects, the relative contribution of cortical regions to motor performance varies with the task parameters. Additionally, after stroke, recruitment of cortical areas during a simple motor task varies with corticospinal system integrity. We investigated whether the pattern of motor system recruitment in a task involving increasingly forceful hand grips is influenced by the degree of corticospinal system damage. Nine chronic subcortical stroke patients and nine age-matched controls underwent functional magnetic brain imaging whilst performing repetitive isometric hand grips. Target grip forces were varied between 15% and 45% of individual maximum grip force. Corticospinal system functional integrity was assessed with transcranial magnetic stimulation. Averaged across all forces, there was more task-related activation compared with rest in the secondary motor areas of patients with greater corticospinal system damage, confirming previous reports. However, here we were primarily interested in regional brain activation, which covaried with the amount of force generated, implying a prominent executive role in force production. We found that in control subjects and patients with lesser corticospinal system damage, signal change increased linearly with increasing force output in contralateral primary motor cortex, supplementary motor area and ipsilateral cerebellum. In contrast, in patients with greater corticospinal system damage, force-related signal changes were seen mainly in contralesional dorsolateral premotor cortex, bilateral ventrolateral premotor cortices and contralesional cerebellum, but not ipsilesional primary motor cortex. These findings suggest that the premotor cortices might play a new and functionally relevant role in controlling force production in patients with more severe corticospinal system disruption.

Cerebral palsy: new approaches to therapy

Cerebral palsy is the most common developmental disorder causing a physical disability arising from an injury to the central nervous system. The majority of pediatric neurologists remain minimally involved in the rehabilitation of these children. Recent advances in basic and clinical neuroscience give hope that effective rehabilitation strategies, based on motor learning science, can be developed for these children. The aim of this review is to alert pediatric neurologists to these advances.

Shifting of activation center in the brain during muscle fatigue: an explanation of minimal central fatigue?

Accumulating evidence suggests that the overall level of cortical activation controlling a voluntary motor task that leads to significant muscle fatigue does not decrease as much as the activation level of the motoneuron pool projecting to the muscle. One possible explanation for this "muscle fatigue>cortical fatigue" phenomenon is that the brain is an organ with built-in redundancies: it has multiple motor centers and parallel pathways, and the center of activation may shift from one location to another when neurons in the previous location become fatigued. This hypothesis was tested by estimating the changes of source locations of high-density (64 channels) scalp electroencephalographic (EEG) signals collected during both fatigue and non-fatigue motor tasks. A current dipole model was used to estimate the EEG sources. The fatigue motor task induced significant muscle fatigue, and the non-fatigue task did not. The EEG signal source that indicated the center of brain activation showed substantial location shifts during the fatigue motor task. The shifts could not be explained by variations of source locations caused by error estimated from the non-fatigue task EEG and simulated data. Compared to the non-fatigue condition, the weighted-center of the source locations for all the participants shifted toward the right hemisphere (ipsilateral to the muscle activation), anterior, and inferior cortical regions under the fatigue condition. Fatigue did not alter dipole (source-signal) strength or the overall level of brain activation. The brain may avoid fatigue by shifting neuron populations that participate in a fatiguing motor task.

Functional Imaging of Intervention Effects in Stroke Motor Rehabilitation

OBJECTIVE

To assess intervention-specific effects on cortical reorganization after stroke as shown by available functional neuroimaging studies.

DATA SOURCES

We searched Medline for clinical trials that contained the terms stroke, reorganization, and recovery, as well as either positron-emission tomography and PET, near-infrared spectroscopy and NIRS, single-photon emission tomography and SPECT, or functional magnetic resonance imaging and functional MRI; we reviewed primary and secondary references.

STUDY SELECTION

Articles that reported neuroimaging findings as a result of a specific treatment involving more than 1 subject were included.

DATA EXTRACTION

We included clinical trials that contained the terms stroke, reorganization, and recovery, as well as functional neuroimaging data findings as a result of a specific treatment involving more than 1 subject.

DATA SYNTHESIS

Included studies differed clearly from one another with regard to patient characteristics, intervention protocol, and outcome measures. Most studies used functional magnetic resonance imaging and a motor paradigm. Studies were limited in size.

CONCLUSIONS

Despite the methodologic differences, several common features can be identified based on the reviewed studies. Clinical improvements occurred even late after injury, after subjects were deemed to have reached a recovery plateau. This clinical improvement was accompanied by cortical reorganization that depended on the type of intervention as well as other factors. This review also suggests direction for future research studies.

The Neural Substrates of Motor Recovery After Focal Damage to the Central Nervous System

OBJECTIVE

To discuss how reorganization of the surviving central nervous system tissue might subserve the improvements in function that are commonly seen over weeks, months, and sometimes years after stroke.

DATA SOURCES

Original scientific studies.

STUDY SELECTION

The studies reviewed all used noninvasive techniques such as functional magnetic resonance imaging, electroencephalography, magnetoencephalography, and transcranial magnetic stimulation. Only studies using motor paradigms in stroke patients were reviewed.

DATA EXTRACTION

Data were reviewed and assessed by the author.

DATA SYNTHESIS

Currently, results suggest that functionally relevant changes do occur in cerebral networks in human stroke patients. For example, it is apparent that initial attempts to move a paretic limb after stroke are associated with widespread activity within the distributed motor system in both cerebral hemispheres. This reliance on nonprimary motor output pathways is unlikely to support full recovery, but improved efficiency of the surviving networks is associated with behavioral gains.

CONCLUSIONS

This review discusses how a better understanding of the relation between these changes and recovery will facilitate the development of novel therapeutic techniques that are based on neurobiologic principles and that are designed to minimize impairment in appropriately targeted patients suffering from stroke.

Compensatory mechanisms in the aging motor system

Motor functions decline with age due to a number of factors. There is interest in whether these changes are reflected in the organisation of the cerebral motor system in older subjects and whether such changes might be in some way compensatory. Most studies in humans have used functional brain imaging techniques to compare motor system activation in younger and older subjects. Interpretation of these results is made more difficult by potential neurovascular changes in older subjects. However, in general, there appears to be greater motor task-related brain activity in a wider network of brain regions in older compared to younger subjects. The evidence that these changes are compensatory in nature is less clear. Incorporation of behavioural and anatomical data will be required in order to fully interpret the functional imaging results.

Post-lesional cerebral reorganisation: evidence from functional neuroimaging and transcranial magnetic stimulation

Reorganisation of cerebral representations has been hypothesised to underlie the recovery from ischaemic brain infarction. The mechanisms can be investigated non-invasively in the human brain using functional neuroimaging and transcranial magnetic stimulation (TMS). Functional neuroimaging showed that reorganisation is a dynamic process beginning after stroke manifestation. In the acute stage, the mismatch between a large perfusion deficit and a smaller area with impaired water diffusion signifies the brain tissue that potentially enables recovery subsequent to early reperfusion as in thrombolysis. Single-pulse TMS showed that the integrity of the cortico-spinal tract system was critical for motor recovery within the first four weeks, irrespective of a concomitant affection of the somatosensory system. Follow-up studies over several months revealed that ischaemia results in atrophy of brain tissue adjacent to and of brain areas remote from the infarct lesion. In patients with hemiparetic stroke activation of premotor cortical areas in both cerebral hemispheres was found to underlie recovery of finger movements with the affected hand. Paired-pulse TMS showed regression of perilesional inhibition as well as intracortical disinhibition of the motor cortex contralateral to the infarction as mechanisms related to recovery. Training strategies can employ post-lesional brain plasticity resulting in enhanced perilesional activations and modulation of large-scale bihemispheric circuits.

Functional neuroimaging studies of cognitive recovery after acquired brain damage in adults

The first two decades of cognitive neuroimaging research have provided a constant increase of the knowledge about the neural organization of cognitive processes. Many cognitive functions (e.g.working memory) can now be associated with particular neural structures, and ongoing research promises to clarify this picture further, providing a new mapping between cognitive and neural function. The main goal of this paper is to outline conceptual issues that are particularly important in the context of imaging changes in neural function through recovery process. This review focuses primarily on studies made in stroke and traumatic brain injury patients, but most of the issues raised here are also relevant to studies using other acquired brain damages. Finally, we summarize a set of methodological issues related to functional neuroimaging that are relevant for the study of neural plasticity and recovery after rehabilitation.

An event-related fMRI study of self-paced alphabetically ordered writing of single letters

The spatial location of activation for writing individual letters and for writing simple dots was studied using event-related functional MRI. Ten healthy right-handed subjects were scanned while performing two different protocols with self-paced repetitive movement. In the first protocol with self-paced dot writing, we observed significant activation in regions known to participate in motor control: contralateral to the movement in the primary sensorimotor and supramarginal cortices, the supplementary motor area (SMA) with the underlying cingulate, in the thalamus and, to a lesser extent, in the ipsilateral inferior parietal and occipital cortices. In the second protocol, we investigated an elemental writing feature--writing single letters. We observed statistically significant changes in the premotor, sensorimotor and supramarginal cortices, the SMA and the thalamus with left predominance, and in the bilateral premotor and inferior/superior parietal cortices. The parietal region that was active during the writing of single letters spanned the border between the parietal superior and inferior lobuli Brodmann area (BA 2, 40), deep in the intraparietal sulcus, with a surprising right-sided dominance. The direct comparison of the results of the two protocols was not significant with a confidence level of P<0.05 corrected for whole brain volume. Thus, the ROI approach was used, and we tried to find significant differences within the two predefined regions of interest (ROI) (BA 7, BA 37). The differences were found with a confidence level of P<0.05 corrected for the volume of these predicted areas. The ROI were located in the posterior parts of hemispheres, in the ventral and in the dorsal visual pathway. The right-sided posterior cortices may play a role in the elemental mechanisms of writing. It is possible that activation of this region is linked with the spatial dimension of the writing.

Neurological recovery after decompressive craniectomy for massive ischemic stroke

INTRODUCTION

Decompressive craniectomy has demonstrated efficacy in reducing morbidity and mortality in critically ill patients with massive hemispheric cerebral infarction. However, little is known about the patterns of functional recovery that exist in patients after decompressive craniectomy, and controversy still exists as to whether craniotomy and infarct resection ("strokectomy") are appropriate alternatives to decompression alone. We therefore used functional magnetic resonance imaging (f-MRI) to assess the extent and location of functional recovery in patients after decompressive craniectomy for massive ischemic stroke.

METHODS

f-MRI was obtained in three patients with massive nondominant cerebral infarction who had undergone decompressive craniectomy for severe cerebral edema 13 to 26 months previously. Brain activation was triggered by hand-gripping or foot- movement tasks. Imaging results were combined with periodic clinical follow-up to determine the extent of neurological recovery.

RESULTS

Activation of the contralateral hemisphere was seen in the sensorimotor cortex, premotor, and supplementary motor areas. Lesser activation patterns were seen in equivalent regions of the infarcted hemisphere. Peri-infarct activation foci were seen in two of the three patients, but no activation occurred within the area of infarction as defined by the initial stroke seen on diffusion-weighted MRI. All three patients demonstrated some corresponding neurological improvement.

CONCLUSION

After massive hemispheric cerebral infarction requiring decompressive craniectomy, patients may experience functional recovery as a result of activation in both the infarcted and contralateral hemispheres. The evidence of functional recovery in peri-infarct regions suggests that decompression alone may be preferable to strokectomy where the risk of damage to adjacent nonischemic brain may be greater.

Intracerebral ERD/ERS in voluntary movement and in cognitive visuomotor task

In order to study cerebral activity related to preparation and execution of movement, evoked and induced brain electrical activities were compared to each other and to fMRI results in voluntary self-paced movements. Also, the event-related desynchronization and synchronization (ERD/ERS) were studied in complex movements with various degrees of cognitive load. The Bereitschaftspotential (BP) and alpha (8-12 Hz) and beta (16-24 Hz) ERD/ERS rhythms in self-paced simple movements were analyzed in 14 epilepsy surgery candidates. In previous studies, the cortical sources of BP were consistently displayed contralateral to the movement in the primary motor cortex and somatosensory cortex, and bilateral in the supplementary motor area (SMA) and in the cingulate cortex. There were also small and inconstant BP generators in the ipsilateral sensorimotor, premotor, and dorsolateral prefrontal cortex. Alpha and beta ERD/ERS were also observed in these cortical regions. The distribution of contacts showing ERD or ERS was larger than of those showing BP. In contrast to BP, ERD, and ERS frequently occurred in the orbitofrontal, lateral and mesial temporal cortices, and inferior parietal lobule. The spatial location of brain activation for self-paced repetitive movements, i.e., writing simple dots, was studied using event-related functional MRI (fMRI) in 10 healthy right-handed subjects. We observed significant activation in regions known to participate in motor control: contralateral to the movement in the primary sensorimotor and supramarginal cortices, the SMA and the underlying cingulate, and, to a lesser extent, the ipsilateral sensorimotor region. When the fMRI was compared with the map of the brain areas electrically active with self-paced movements (intracerebral recordings; Rektor et al., 1994, 1998, 2001b, c; Rektor, 2003), there was an evident overlap of most results. Nevertheless, the electrophysiological studies were more sensitive in uncovering small active areas, i.e., in the premotor and prefrontal cortices. The BP and the event-related hemodynamic changes were displayed in regions known to participate in motor control. The cortical occurrence of oscillatory activities in the alpha-beta range was clearly more widespread. Four epilepsy surgery candidates with implanted depth brain electrodes performed two visuomotor-cognitive tasks with cued complex movements: a simple task--copying randomly presented letters from the monitor; and a more complex task--writing a letter other than that which appears on the monitor. The second task demanded an increased cognitive load, i.e., of executive functions. Alpha and beta ERD/ERS rhythms were evaluated. Similar results for both tasks were found in the majority of the frontal contacts, i.e., in the SMA, anterior cingulate, premotor, and dorsolateral prefrontal cortices. The most frequent observed activity was ERD in the beta rhythm; alpha ERS and ERD were also present. Significant differences between the two tasks appeared in several frontal areas--in the dorsolateral and ventrolateral prefrontal and orbitofrontal cortices (BA 9, 45, 11), and in the temporal neocortex (BA 21). In several contacts localized in these areas, namely in the lateral temporal cortex, there were significant changes only with the complex task--mostly beta ERD. Although the fMRI results fit well with the map of the evoked activity (BP), several discrepant localizations were displayed when the BP was compared with the distribution of the oscillatory activity (ERD-ERS). The BP and hemodynamic changes are closely related to the motor control areas; ERD/ERS represent the broader physiological aspects of motor execution and control. The BP probably reflects regional activation, while the more widespread ERD/ERS may reflect the spread of task-relevant information across relevant areas. In the writing tasks, the spatial distribution of the alpha-beta ERD/ERS in the frontal and lateral temporal cortices was partially task dependent. The ERD/ERS occurred there predominantly in the more complex of the writing tasks. Some sites were only active in the task with the increased demand on executive functions. In the temporal neocortex only, the oscillatory, but not the evoked, activity was recorded in the self-paced movement. The temporal appearance of changes of oscillatory activities in the self-paced movement task as well as in the cued movement task with an increased load of executive functions raises the interesting question of the role of this region in cognitive-movement information processing.

An Event-Related fMRI Study of Self-Paced Writing of Simple Dots

The spatial locations of brain activation related to self-paced repetitive movements, i.e., writing simple dots, were studied using event-related fMRI. Ten healthy right-handed subjects were scanned while performing the protocol with self-paced repetitive movement. In a protocol with self-paced dot writing, we observed significant activation in regions known to participate in motor control: Contralateral to the movement in the primary sensorimotor and supramarginal cortices, the supplementary motor area (SMA) and the underlying cingulate, and, to a lesser extent, the sensorimotor region ipsilateral to the writing hand. When the fMRI was compared with the map of the brain areas electrically active with self-paced movements (intracerebral recordings; Rektor et al., 1994 , 1998 , 2001, b , c , 2003 ), there was an evident overlap of most results. Nevertheless, the electrophysiological studies were more sensitive in uncovering small active areas, i.e., in the premotor and prefrontal cortices. The Bereitschafspotential (BP) with Movement Accompanying Potential (MAP) and hemodynamic changes overlap in regions where the BP were displayed consistently. In some other regions, the BP recordings were inconsistent, i.e., in the prefrontal cortex, where about half of the contacts displayed BP generators while the other half did not. In these regions the hemodynamic changes were not significant. The spatial limitations of the intracerebral electrodes is a result of the fact that the electrodes are submerged in the cerebral tissue and record in their immediate vicinity. The fMRI that indirectly measures activity of larger populations of neurons has better spatial resolution. Electrophysiological techniques with intracranial recordings may reveal even subtle generators of electrical activity.

Adaptation of the attention network in human immunodeficiency virus brain injury

Human immunodeficiency virus (HIV)-positive patients commonly have attention and concentration problems. However, it remains unclear how HIV infection affects the attention network. Therefore, blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) was performed in 36 subjects (18 HIV and 18 seronegative [SN] controls) during a set of visual attention tasks with increasing levels of attentional load. Compared with SN controls, HIV subjects showed similar task performance (accuracies and reaction times) but decreased activation in the normal visual attention network (dorsal parietal, bilateral prefrontal, and cerebellar regions) and increased activation in adjacent or contralateral brain regions. Cognitive performance (assessed with NPZ-8), CD4, and viral load all correlated with activated BOLD signals in brain regions that activated more in HIV subjects. Furthermore, HIV subjects activated more than SN controls in brain regions that showed load-dependent increase in activation (right prefrontal and right parietal regions) but less in regions that showed a saturation effect with increasing load. These findings suggest that HIV-associated brain injury leads to reduced efficiency in the normal attention network, thus requiring reorganization and increased usage of neural reserves to maintain performance during attention-requiring tasks. Exceeding the brain reserve capacity may lead to attention deficits and cognitive impairment in HIV patients.

Motor representation in patients rapidly recovering after stroke: a functional magnetic resonance imaging and transcranial magnetic stimulation study

OBJECTIVE

Neuroimaging studies have suggested an evolution of the brain activation pattern in the course of motor recovery after stroke. Initially poor motor performance is correlated with an recruitment of the uninjured hemisphere that continuously vanished until a nearly normal (contralateral) activation pattern is achieved and motor performance is good. Here we were interested in the early brain activation pattern in patients who showed a good and rapid recovery after stroke.

METHODS

Ten patients with first-ever ischemic stroke affecting motor areas had to perform self-paced simple or more complex movements with the affected or the unaffected hand during functional magnetic resonance imaging (fMRI). The location and number of activated voxels above threshold were determined. To study possible changes in the cortical motor output map the amplitude of the motor evoked potentials (MEP) and the extent of the excitable area were determined using transcranial magnetic stimulation (TMS).

RESULTS

The pattern of activation observed with movements of the affected and the unaffected hand was similar. In the simple motor task significant (P<0.05) increases were found in the primary motor cortex ipsilateral to the movement, the supplementary motor area and the cerebellar hemisphere contralateral to the movement during performance with the affected hand compared to movements with the unaffected hand. When comparing simple with more complex movements performed with either the affected or the unaffected hand, a further tendency to increased activation in motor areas was observed. The amplitude of MEPs obtained from the affected hemisphere was smaller and the extent of cortical output maps was decreased compared to the unaffected hemisphere; but none of the patients showed MEPs at the affected hand when the ipsilateral unaffected motor cortex was stimulated.

CONCLUSIONS

Despite a rapid and nearly complete motor recovery the brain activation pattern was associated with increased activity in (bilateral) motor areas as revealed with fMRI. TMS revealed impaired motor output properties, but failed to demonstrate ipsilateral motor pathways. Successful recovery in our patients may therefore rely on the increased bilateral activation of existing motor networks spared by the injury.