Answering the call: the influence of neuroimaging and electrophysiological evidence on rehabilitation

Immediate effects of noxious and innocuous thermal stimulation on brain activation in patients with stroke

Case-control studies have shown that noxious thermal stimulation (TS) can improve arm function in patients with stroke. However, the neural mechanisms underlying this improvement are largely unknown. We explored functional neural activation due to noxious and innocuous TS intervention applied to the paretic arm of patients with stroke. Sixteen participants with unilateral cortical infarctions were allocated to one of two groups: noxious TS (8 patients; temperature combination: hot pain 46°C to 47°C, cold pain 7°C-8°C) or innocuous TS (n = 8; temperature combination: hot 40°C-41°C, cold 20°C-21°C). All subjects underwent fMRI scanning before and after 30 min TS intervention and performed a finger tapping task with the affected hand. Immediate brain activation effects were assessed according to thermal type (noxious vs. innocuous TS) and time (pre-TS vs post-TS). Regions activated by noxious TS relative to innocuous TS (P < .05, adjusted for multiple comparisons) were related to motor performance and sensory function in the bilateral primary somatosensory cortices, anterior cingulate cortex, insula, thalamus, hippocampus and unilateral primary motor cortex, secondary somatosensory cortex at the contralateral side of lesion, and unilateral supplementary motor area at the ipsilateral side of lesion. Greater activation responses were observed in the side contralateral to the lesion, suggesting a significant intervention effect. Our preliminary findings suggest that noxious TS may induce neuroplastic changes unconstrained to the local area.Trial registration: NCT01418404.

Cognitive load reduces the effects of optic flow on gait and electrocortical dynamics during treadmill walking

During navigation of complex environments, the brain must continuously adapt to both external demands, such as fluctuating sensory inputs, and internal demands, such as engagement in a cognitively demanding task. Previous studies have demonstrated changes in behavior and gait with increased sensory and cognitive load, but the underlying cortical mechanisms remain largely unknown. In the present study, in a mobile brain/body imaging (MoBI) approach, 16 young adults walked on a treadmill with high-density EEG while 3-dimensional (3D) motion capture tracked kinematics of the head and feet. Visual load was manipulated with the presentation of optic flow with and without continuous mediolateral perturbations. The effects of cognitive load were assessed by the performance of a go/no-go task on half of the blocks. During increased sensory load, participants walked with shorter and wider strides, which may indicate a more restrained pattern of gait. Interestingly, cognitive task engagement attenuated these effects of sensory load on gait. Using an independent component analysis and dipole-fitting approach, we found that cautious gait was accompanied by neuro-oscillatory modulations localized to frontal (supplementary motor area, anterior cingulate cortex) and parietal (inferior parietal lobule, precuneus) areas. Our results show suppression in alpha/mu (8-12 Hz) and beta (13-30 Hz) rhythms, suggesting enhanced activation of these regions with unreliable sensory inputs. These findings provide insight into the neural correlates of gait adaptation and may be particularly relevant to older adults who are less able to adjust to ongoing cognitive and sensory demands while walking. NEW & NOTEWORTHY The neural underpinnings of gait adaptation in humans are poorly understood. To this end, we recorded high-density EEG combined with three-dimensional body motion tracking as participants walked on a treadmill while exposed to full-field optic flow stimulation. Perturbed visual input led to a more cautious gait pattern with neuro-oscillatory modulations localized to premotor and parietal regions. Our findings show a possible brain-behavior link that might further our understanding of gait and mobility impairments.

Insights and Perspectives on Sensory-Motor Integration and Rehabilitation

The present review focuses on the flow and interaction of somatosensory-motor signals in the central and peripheral nervous system. Specifically, where incoming sensory signals from the periphery are processed and interpreted to initiate behaviors, and how ongoing behaviors produce sensory consequences encoded and used to fine-tune subsequent actions. We describe the structure–function relations of this loop, how these relations can be modeled and aspects of somatosensory-motor rehabilitation. The work reviewed here shows that it is imperative to understand the fundamental mechanisms of the somatosensory-motor system to restore accurate motor abilities and appropriate somatosensory feedback. Knowledge of the salient neural mechanisms of sensory-motor integration has begun to generate innovative approaches to improve rehabilitation training following neurological impairments such as stroke. The present work supports the integration of basic science principles of sensory-motor integration into rehabilitation procedures to create new solutions for sensory-motor disorders.

Early childhood constraint therapy for sensory/motor impairment in cerebral palsy: a randomised clinical trial protocol

INTRODUCTION

Cerebral palsy (CP) is the most common physical disability in childhood. It is a disorder resulting from sensory and motor impairments due to perinatal brain injury, with lifetime consequences that range from poor adaptive and social function to communication and emotional disturbances. Infants with CP have a fundamental disadvantage in recovering motor function: they do not receive accurate sensory feedback from their movements, leading to developmental disregard. Constraint-induced movement therapy (CIMT) is one of the few effective neurorehabilitative strategies shown to improve upper extremity motor function in adults and older children with CP, potentially overcoming developmental disregard.

METHODS AND ANALYSIS

This study is a randomised controlled trial of children 12-24 months corrected age studying the effectiveness of CIMT combined with motor and sensory-motor interventions. The study population will comprise 72 children with CP and 144 typically developing children for a total of N=216 children. All children with CP, regardless of group allocation will continue with their standard of care occupational and physical therapy throughout the study. The research material collected will be in the form of data from high-density array event-related potential scan, standardised assessment scores and motion analysis scores.

ETHICS AND DISSEMINATION

The study protocol was approved by the Institutional Review Board. The findings of the trial will be disseminated through peer-reviewed journals and scientific conferences.

TRIAL REGISTRATION NUMBER

NCT02567630.

A Review of Transcranial Magnetic Stimulation and Multimodal Neuroimaging to Characterize Post-Stroke Neuroplasticity

Following stroke, the brain undergoes various stages of recovery where the central nervous system can reorganize neural circuitry (neuroplasticity) both spontaneously and with the aid of behavioral rehabilitation and non-invasive brain stimulation. Multiple neuroimaging techniques can characterize common structural and functional stroke-related deficits, and importantly, help predict recovery of function. Diffusion tensor imaging (DTI) typically reveals increased overall diffusivity throughout the brain following stroke, and is capable of indexing the extent of white matter damage. Magnetic resonance spectroscopy (MRS) provides an index of metabolic changes in surviving neural tissue after stroke, serving as a marker of brain function. The neural correlates of altered brain activity after stroke have been demonstrated by abnormal activation of sensorimotor cortices during task performance, and at rest, using functional magnetic resonance imaging (fMRI). Electroencephalography (EEG) has been used to characterize motor dysfunction in terms of increased cortical amplitude in the sensorimotor regions when performing upper limb movement, indicating abnormally increased cognitive effort and planning in individuals with stroke. Transcranial magnetic stimulation (TMS) work reveals changes in ipsilesional and contralesional cortical excitability in the sensorimotor cortices. The severity of motor deficits indexed using TMS has been linked to the magnitude of activity imbalance between the sensorimotor cortices. In this paper, we will provide a narrative review of data from studies utilizing DTI, MRS, fMRI, EEG, and brain stimulation techniques focusing on TMS and its combination with uni- and multimodal neuroimaging methods to assess recovery after stroke. Approaches that delineate the best measures with which to predict or positively alter outcomes will be highlighted.

Associations between Proprioceptive Neural Pathway Structural Connectivity and Balance in People with Multiple Sclerosis

Mobility and balance impairments are a hallmark of multiple sclerosis (MS), affecting nearly half of patients at presentation and resulting in decreased activity and participation, falls, injuries, and reduced quality of life. A growing body of work suggests that balance impairments in people with mild MS are primarily the result of deficits in proprioception, the ability to determine body position in space in the absence of vision. A better understanding of the pathophysiology of balance disturbances in MS is needed to develop evidence-based rehabilitation approaches. The purpose of the current study was to (1) map the cortical proprioceptive pathway in vivo using diffusion-weighted imaging and (2) assess associations between proprioceptive pathway white matter microstructural integrity and performance on clinical and behavioral balance tasks. We hypothesized that people with MS (PwMS) would have reduced integrity of cerebral proprioceptive pathways, and that reduced white matter microstructure within these tracts would be strongly related to proprioceptive-based balance deficits. We found poorer balance control on proprioceptive-based tasks and reduced white matter microstructural integrity of the cortical proprioceptive tracts in PwMS compared with age-matched healthy controls (HC). Microstructural integrity of this pathway in the right hemisphere was also strongly associated with proprioceptive-based balance control in PwMS and controls. Conversely, while white matter integrity of the right hemisphere’s proprioceptive pathway was significantly correlated with overall balance performance in HC, there was no such relationship in PwMS. These results augment existing literature suggesting that balance control in PwMS may become more dependent upon (1) cerebellar-regulated proprioceptive control, (2) the vestibular system, and/or (3) the visual system.

The effects of augmented visual feedback during balance training in Parkinson's disease: study design of a randomized clinical trial

BACKGROUND

Patients with Parkinson's disease often suffer from reduced mobility due to impaired postural control. Balance exercises form an integral part of rehabilitative therapy but the effectiveness of existing interventions is limited. Recent technological advances allow for providing enhanced visual feedback in the context of computer games, which provide an attractive alternative to conventional therapy. The objective of this randomized clinical trial is to investigate whether a training program capitalizing on virtual-reality-based visual feedback is more effective than an equally-dosed conventional training in improving standing balance performance in patients with Parkinson's disease.

METHODS/DESIGN

Patients with idiopathic Parkinson's disease will participate in a five-week balance training program comprising ten treatment sessions of 60 minutes each. Participants will be randomly allocated to (1) an experimental group that will receive balance training using augmented visual feedback, or (2) a control group that will receive balance training in accordance with current physical therapy guidelines for Parkinson's disease patients. Training sessions consist of task-specific exercises that are organized as a series of workstations. Assessments will take place before training, at six weeks, and at twelve weeks follow-up. The functional reach test will serve as the primary outcome measure supplemented by comprehensive assessments of functional balance, posturography, and electroencephalography.

DISCUSSION

We hypothesize that balance training based on visual feedback will show greater improvements on standing balance performance than conventional balance training. In addition, we expect that learning new control strategies will be visible in the co-registered posturographic recordings but also through changes in functional connectivity.

Developmental coordination disorder: a review and update

Present in approximately 5-6% of school-aged children, developmental coordination disorder (DCD) is a neuromotor disability in which a child's motor coordination difficulties significantly interfere with activities of daily living or academic achievement. These children typically have difficulty with fine and/or gross motor skills, with motor performance that is usually slower, less accurate, and more variable than that of their peers. In this paper, we review the history of various definitions leading up to the current definition of DCD, prevalence estimates for the disorder, etiology, common co-morbidities, the impact of DCD on the child's life, and prognosis. As well, we briefly describe current interventions for children with the disorder and results of recent neuroimaging studies of the brains of children with DCD, including research by the authors of this paper.

Neuroplasticity and its applications for rehabilitation

Stroke represents a major cause of death and disability. In just the last two decades, science has begun to appreciate the central nervous system's attempts to repair itself through a process termed neuroplasticity. The remodeling is a dynamic process subject to endogenous and exogenous forces. Rehabilitation has started to implement approaches based on objective measures such as diffusion tensor imaging and functional magnetic resonance. Newer modalities such as constraint-induced movement therapy and robotic interventions are being used for both short- and long-term functional gains. This review describes the various studies on neuroplasticity and the variety of interventions now available.

Level of participation in robotic-assisted treadmill walking modulates midline sensorimotor EEG rhythms in able-bodied subjects

In robot assisted gait training, a pattern of human locomotion is executed repetitively with the intention to restore the motor programs associated with walking. Several studies showed that active contribution to the movement is critical for the encoding of motor memory. We propose to use brain monitoring techniques during gait training to encourage active participation in the movement. We investigated the spectral patterns in the electroencephalogram (EEG) that are related to active and passive robot assisted gait. Fourteen healthy participants were considered. Infomax independent component analysis separated the EEG into independent components representing brain, muscle, and eye movement activity, as well as other artifacts. An equivalent current dipole was calculated for each independent component. Independent components were clustered across participants based on their anatomical position and frequency spectra. Four clusters were identified in the sensorimotor cortices that accounted for differences between active and passive walking or showed activity related to the gait cycle. We show that in central midline areas the mu (8-12 Hz) and beta (18-21 Hz) rhythms are suppressed during active compared to passive walking. These changes are statistically significant: mu (F(1, 13)=11.2 p ≤ 0.01) and beta (F(1, 13)=7.7, p ≤ 0.05). We also show that these differences depend on the gait cycle phases. We provide first evidence of modulations of the gamma rhythm in the band 25 to 40 Hz, localized in central midline areas related to the phases of the gait cycle. We observed a trend (F(1, 8)=11.03, p ≤ 0.06) for suppressed low gamma rhythm when comparing active and passive walking. Additionally we found significant suppressions of the mu (F(1, 11)=20.1 p ≤ 0.01), beta (F(1, 11)=11.3 p ≤ 0.05) and gamma (F(1, 11)=4.9 p ≤ 0.05) rhythms near C3 (in the right hand area of the primary motor cortex) during phases of active vs. passive robot assisted walking. To our knowledge this is the first study showing EEG analysis during robot assisted walking. We provide evidence for significant differences in cortical activation between active and passive robot assisted gait. Our findings may help to define appropriate features for single trial detection of active participation in gait training. This work is a further step toward the evaluation of brain monitoring techniques and brain-computer interface technologies for improving gait rehabilitation therapies in a top-down approach.

An EEG-based study of discrete isometric and isotonic human lower limb muscle contractions

Background

Electroencephalography (EEG) combined with independent component analysis enables functional neuroimaging in dynamic environments including during human locomotion. This type of functional neuroimaging could be a powerful tool for neurological rehabilitation. It could enable clinicians to monitor changes in motor control related cortical dynamics associated with a therapeutic intervention, and it could facilitate noninvasive electrocortical control of devices for assisting limb movement to stimulate activity dependent plasticity. Understanding the relationship between electrocortical dynamics and muscle activity will be helpful for incorporating EEG-based functional neuroimaging into clinical practice. The goal of this study was to use independent component analysis of high-density EEG to test whether we could relate electrocortical dynamics to lower limb muscle activation in a constrained motor task. A secondary goal was to assess the trial-by-trial consistency of the electrocortical dynamics by decoding the type of muscle action.

Methods

We recorded 264-channel EEG while 8 neurologically intact subjects performed isometric and isotonic, knee and ankle exercises at two different effort levels. Adaptive mixture independent component analysis (AMICA) parsed EEG into models of underlying source signals. We generated spectrograms for all electrocortical source signals and used a naïve Bayesian classifier to decode exercise type from trial-by-trial time-frequency data.

Results

AMICA captured different electrocortical source distributions for ankle and knee tasks. The fit of single-trial EEG to these models distinguished knee from ankle tasks with 80% accuracy. Electrocortical spectral modulations in the supplementary motor area were significantly different for isometric and isotonic tasks (p < 0.05). Isometric contractions elicited an event related desynchronization (ERD) in the α-band (8–12 Hz) and β-band (12–30 Hz) at joint torque onset and offset. Isotonic contractions elicited a sustained α- and β-band ERD throughout the trial. Classifiers based on supplementary motor area sources achieved a 4-way classification accuracy of 69% while classifiers based on electrocortical sources in multiple brain regions achieved a 4-way classification accuracy of 87%.

Conclusions

Independent component analysis of EEG reveals unique spatial and spectro-temporal electrocortical properties for different lower limb motor tasks. Using a broad distribution of electrocortical signals may improve classification of human lower limb movements from single-trial EEG.

Associations between gait patterns, brain lesion factors and functional recovery in stroke patients

Brain CT scans and neurological condition were evaluated in 74 stroke patients. Firstly, we found that using a classification-tree technique based on CT scan parameters (an innovative method, analyzing four parameters simultaneously) coincided with our previously proposed kinematic artificial neural network (ANN) classification technique for 71.3% of patients. Lesion size and location were found to be the most significant CT scan predictors of gait classification. Secondly, we sought to gauge post-rehabilitation functional recovery in patients within the same three groups of gait pattern. We found significant differences in scores between the three gait pattern groups, before and after rehabilitation (Kruskal-Wallis test, p<0.001), while significant improvement was observed in each group (Wilcoxon text; p<0.01). We conclude that patient classification into pathological gait groups on the basis of gait or CT scan parameters may serve as an early predictor of future functional outcome.

Implicit sequence-specific motor learning after subcortical stroke is associated with increased prefrontal brain activations: an fMRI study

Implicit motor learning is preserved after stroke, but how the brain compensates for damage to facilitate learning is unclear. We used a random effects analysis to determine how stroke alters patterns of brain activity during implicit sequence-specific motor learning as compared to general improvements in motor control. Nine healthy participants and nine individuals with chronic, right focal subcortical stroke performed a continuous joystick-based tracking task during an initial functional magnetic resonance images (fMRI) session, over 5 days of practice, and a retention test during a separate fMRI session. Sequence-specific implicit motor learning was differentiated from general improvements in motor control by comparing tracking performance on a novel, repeated tracking sequence during early practice and again at the retention test. Both groups demonstrated implicit sequence-specific motor learning at the retention test, yet substantial differences were apparent. At retention, healthy control participants demonstrated increased blood oxygenation level dependent (BOLD) response in left dorsal premotor cortex (PMd; BA 6) but decreased BOLD response left dorsolateral prefrontal cortex (DLPFC; BA 9) during repeated sequence tracking. In contrast, at retention individuals with stroke did not show this reduction in DLPFC during repeated tracking. Instead implicit sequence-specific motor learning and general improvements in motor control were associated with increased BOLD response in the left middle frontal gyrus BA 8, regardless of sequence type after stroke. These data emphasize the potential importance of a prefrontal-based attentional network for implicit motor learning after stroke. This study is the first to highlight the importance of the prefrontal cortex for implicit sequence-specific motor learning after stroke.

Electrocortical activity is coupled to gait cycle phase during treadmill walking

Recent findings suggest that human cortex is more active during steady-speed unperturbed locomotion than previously thought. However, techniques that have been used to image the brain during locomotion lack the temporal resolution necessary to assess intra-stride cortical dynamics. Our aim was to determine if electrocortical activity is coupled to gait cycle phase during steady-speed human walking. We used electroencephalography (EEG), motion capture, and a force-measuring treadmill to record brain and body dynamics while eight healthy young adult subjects walked on a treadmill. Infomax independent component analysis (ICA) parsed EEG signals into maximally independent component (IC) processes representing electrocortical sources, muscle sources, and artifacts. We calculated a spatially fixed equivalent current dipole for each IC using an inverse modeling approach, and clustered electrocortical sources across subjects by similarities in dipole locations and power spectra. We then computed spectrograms for each electrocortical source that were time-locked to the gait cycle. Electrocortical sources in the anterior cingulate, posterior parietal, and sensorimotor cortex exhibited significant (p<0.05) intra-stride changes in spectral power. During the end of stance, as the leading foot was contacting the ground and the trailing foot was pushing off, alpha- and beta-band spectral power increased in or near the left/right sensorimotor and dorsal anterior cingulate cortex. Power increases in the left/right sensorimotor cortex were more pronounced for contralateral limb push-off (ipsilateral heel-strike) than for ipsilateral limb push-off (contralateral heel-strike). Intra-stride high-gamma spectral power changes were evident in anterior cingulate, posterior parietal, and sensorimotor cortex. These data confirm cortical involvement in steady-speed human locomotion. Future applications of these techniques could provide critical insight into the neural mechanisms of movement disorders and gait rehabilitation.

One-year retention of general and sequence-specific skills in a probabilistic, serial reaction time task

Procedural skills such as riding a bicycle and playing a musical instrument play a central role in daily life. Such skills are learned gradually and are retained throughout life. The present study investigated 1-year retention of procedural skill in a version of the widely used serial reaction time task (SRTT) in young and older motor-skill experts and older controls in two experiments. The young experts were college-age piano and action video-game players, and the older experts were piano players. Previous studies have reported sequence-specific skill retention in the SRTT as long as 2 weeks but not at 1 year. Results indicated that both young and older experts and older non-experts revealed sequence-specific skill retention after 1 year with some evidence that general motor skill was retained as well. These findings are consistent with theoretical accounts of procedural skill learning such as the procedural reinstatement theory as well as with previous studies of retention of other motor skills.

The role of functional magnetic resonance imaging in the study of brain development, injury, and recovery in the newborn

Development of brain functions and the structural-functional correlates of brain injury remain difficult to evaluate in the young infant. Thus, new noninvasive methods capable of early functional diagnosis are needed. This review describes the use of functional magnetic resonance imaging (fMRI) for studying localization of brain function in the developing brain when standard clinical investigations are not available or conclusive. This promising neuroimaging technique has been successfully used in healthy newborns and in newborns with brain injury using different paradigms, including passive visual, somato-sensorial, and auditory stimulation. We summarize the major findings of previous fMRI studies in young infants, describe ongoing methodological challenges, and propose exciting future developments in using resting-state protocols and functional connectivity techniques to assist in evaluating early life brain function and its recovery from injury.

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.

Association between gait asymmetry and brain lesion location in stroke patients

BACKGROUND AND PURPOSE

Associations between the site of brain injury and poststroke gait impairment are poorly understood. Temporal gait asymmetry after stroke is a salient index of gait dysfunction that has important functional consequences. The current study investigated whether subtraction lesion analysis could distinguish brain regions associated with persisting temporal gait asymmetry in chronic stroke patients.

METHODS

Analysis was conducted on 37 chronic ambulatory stroke patients (17 symmetrical gait, 20 asymmetrical gait). Spatiotemporal gait parameters were recorded using an instrumented walking surface. Lesions were traced from 3D T1-MRI, and region of interest images were generated. The lesion overlay of patients with symmetrical gait was subtracted from patients with asymmetrical gait to highlight voxels more frequently lesioned in asymmetrical patients and relatively spared in symmetrical patients.

RESULTS

Demographic data were comparable between the 2 groups. Asymmetrical patients exhibited significantly higher National Institute of Health Stroke Scale neglect scores and more severe motor impairment. Gait asymmetry was significantly correlated to Chedoke-McMaster Stroke Scale leg (r=-0.767, P<0.001) and foot (r=-0.759, P<0.001) scores, whereas gait speed correlated less strongly. After subtraction analysis, injury to the posterolateral putamen was evident 60% to 80% more frequently in the asymmetrical group compared to the symmetrical group.

CONCLUSIONS

In this sample of ambulatory chronic stroke patients, damage to the posterolateral putamen was associated with temporal gait asymmetry. Further advances in our understanding of the neural correlates of gait asymmetry may provide prognostic markers for future persistent gait dysfunction and lead to early targeted rehabilitation when key regions are damaged.