Posts Tagged brain activation
[ARTICLE] Increased Sensorimotor Cortex Activation With Decreased Motor Performance During Functional Upper Extremity Tasks Poststroke – Full Text
Background and Purpose: Current literature has focused on identifying neuroplastic changes associated with stroke through tasks and in positions that are not representative of functional rehabilitation. Emerging technologies such as functional near-infrared spectroscopy (fNIRS) provide new methods of expanding the area of neuroplasticity within rehabilitation. This study determined the differences in sensorimotor cortex activation during unrestrained reaching and gripping after stroke.
Methods: Eleven individuals with chronic stroke and 11 neurologically healthy individuals completed reaching and gripping tasks under 3 conditions using their (1) stronger, (2) weaker, and (3) both arms together. Performance and sensorimotor cortex activation using fNIRS were collected. Group and arm differences were calculated using mixed analysis of covariance (covariate: age). Pairwise comparisons were used for post hoc analyses. Partial Pearson correlations between performance and activation were assessed for each task, group, and hemisphere.
Results: Larger sensorimotor activations in the ipsilesional hemisphere were found for the stroke compared with healthy group for reaching and gripping conditions despite poorer performance. Significant correlations were observed between gripping performance (with the weaker arm and both arms simultaneously) and sensorimotor activation for the stroke group only.
Discussion and Conclusions: Stroke leads to significantly larger sensorimotor activation during functional reaching and gripping despite poorer performance. This may indicate an increased sense of effort, decreased efficiency, or increased difficulty after stroke. fNIRS can be used for assessing differences in brain activation during movements in functional positions after stroke. This can be a promising tool for investigating possible neuroplastic changes associated with functional rehabilitation interventions in the stroke population.
Video Abstract available for more insights from the authors (see Video Abstract, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A269).
Stroke is the leading cause of long-term disability in Canada, with approximately 405 000 Canadians currently living with its long-lasting effects.1 While the site of injury and the specific presentation of symptoms are heterogeneous, up to 70% of these individuals experience upper extremity hemiparesis,2 and even after rehabilitation, greater than 65% of this population have difficulty utilizing their affected limb in activities of daily living.3 Decreased use of the paretic arm can lead to chronic pain and weakness, decreased bone density,4 cerebral cortex changes,5and an overall decrease in quality of life.6 In addition, stroke rehabilitation and continual care are costly for the health care system.7 Therefore, it is important to maximize patient recovery in an effective and efficient manner.
One area that has been highly debated for rehabilitation efficacy is the side of arm training. Numerous reviews have stated conflicting and inconclusive results pertaining to benefits of the paretic (affected) arm or bilateral arm training8–10 and a few studies have recently investigated the effects of the nonparetic (less-affected) arm training.11,12 Investigating how stroke itself affects neural activation during unilateral and bilateral upper extremity activities may help explain the mechanisms underlying such training.
In individuals living with the chronic effects of stroke, nonnormal brain activation is commonly seen with irregular activation in both the ipsi- and contralesional hemispheres during movement. A meta-analysis of 20 studies13 calculated increases in contralesional primary motor cortex, and bilateral premotor and supplementary motor areas with use of the paretic hand compared with healthy individuals. Systematically reviewing 22 functional magnetic resonance imaging (fMRI) and positron emission tomography studies, Buma et al14 reported general initial increases in contra-, ipsi-, and perilesional activation during paretic upper extremity movement in individuals with cortical and subcortical strokes when compared with healthy adults. In addition, as paretic arm performance increased with training, these authors also showed that in many, but not all participants, activation decreased in areas such as the contralesional motor cortex (ie, ipsilateral to the movement arm), which is not typically activated in healthy individuals. Previous reviews have also reported increases in cortical activation of motor supporting areas (bilateral premotor and supplementary motor areas) later in recovery that are associated with greater function,15 although the opposite has also been reported.16
The majority of previously mentioned evidence utilized neuroimaging techniques that require an individual to remain fairly still, especially at the head, and recorded in the supine position. While there are many advantages to these techniques, such as high spatial resolution and penetration depth using fMRI, the functional imaging data acquired from these studies may not be truly indicative of the neural correlates involved during rehabilitation tasks. Thus, assessment of brain activation during upright, unrestrained, functional tasks is needed. Functional near-infrared spectroscopy (fNIRS) is an emerging neuroimaging device that has the capabilities of determining cortical activation while the participant is mobile. Similar to fMRI, fNIRS is an indirect measure of cortical activation that utilizes the neurovascular coupling theory to estimate changes in brain activity.17 Near-infrared light emitted by this device is absorbed by areas high in oxyhemoglobin or deoxyhemoglobin content and is measured through detectors placed on the individual’s head. When an increase in brain activity occurs, a typical overall increase in oxyhemoglobin concentration and a slight decrease in deoxyhemoglobin are observed.17 Due to its portability, fNIRS has been used to investigate cortical activation during various mobile tasks after stroke.18,19 To our knowledge, no work has been done to compare sensorimotor cortex activation of paretic, nonparetic, and bilateral arm movements poststroke using fNIRS.
Therefore, the primary purpose of this study was to investigate differences in cortical brain activation during performance of upper extremity activities in an upright position after stroke and in neurologically healthy individuals. Based on the current evidence, we hypothesized that greater sensorimotor cortex activation would be observed in the stroke group compared with the neurologically healthy group, particularly when using the weaker arm. For our secondary measures, we hypothesize that (1) individuals in the stroke group will perform worse than the control group when using their weaker arm and (2) cortical activation in the contralateral hemisphere (eg, ipsilesional hemisphere during paretic arm movements) will positively correlate with task performance.[…]
[ARTICLE] Brain activation is related to smoothness of upper limb movements after stroke – Full Text
It is unclear whether additionally recruited sensorimotor areas in the ipsilesional and contralesional hemisphere and the cerebellum can compensate for lost neuronal functions after stroke. The objective of this study was to investigate how increased recruitment of secondary sensorimotor areas is associated with quality of motor control after stroke. In seventeen patients (three females, fourteen males; age: 59.9 ± 12.6 years), cortical activation levels were determined with functional magnetic resonance imaging (fMRI) in 12 regions of interest during a finger flexion–extension task in weeks 6 and 29 after stroke. At the same time points and by using 3D kinematics, the quality of motor control was assessed by smoothness of the grasp aperture during a reach-to-grasp task, quantified by normalized jerk. Ipsilesional premotor cortex, insula and cerebellum, as well as the contralesional supplementary motor area, insula and cerebellum, correlated significantly and positively with the normalized jerk of grasp aperture at week 6 after stroke. A positive trend towards this correlation was observed in week 29. This study suggests that recruitment of secondary motor areas at 6 weeks after stroke is highly associated with increased jerk during reaching and grasping. As jerk represents the change in acceleration, the recruitment of additional sensorimotor areas seems to reflect a type of control in which deviations from an optimal movement pattern are continuously corrected. This relationship suggests that additional recruitment of sensorimotor areas after stroke may not correspond to restitution of motor function, but more likely to adaptive motor learning strategies to compensate for motor impairments.
Outcomes of neurorehabilitation after stroke are variable and depend largely on the intensity and task specificity of the intervention applied as well as the severity of initial impairment at stroke onset (Langhorne et al. 2011). For the paretic upper limb in particular, treatment effects are mainly restricted to patients with some voluntary control of finger extension after stroke (Kwakkel and Kollen 2013; Langhorne et al. 2011). These findings suggest that there is a need for a better understanding of the neuronal mechanisms underlying functional recovery after stroke.
Task-related recruitment of secondary sensorimotor areas in the affected and non-affected hemisphere has been associated with poor motor recovery in terms of body functions and activities (Buma et al. 2010; Ward et al. 2004). It is therefore unlikely that secondary sensorimotor areas are able to take over the functions of the primary injured motor areas (Buma et al. 2010; Ward et al. 2004). Recruitment of these additional areas may rather reflect support in the execution of compensatory motor control while performing a motor task with the paretic upper limb.
However, it is still unclear how brain activation patterns are associated with quality of upper limb control after stroke (Buma et al. 2013). Most traditional clinical assessment scales are not suitable for capturing howpatients perform functional tasks. By contrast, 3D kinematics can assess intra-limb coordination and smoothness of movement patterns, which are important characteristics of quality of motor control.
A recent study with intensive repeated 3D kinematic measurements in the first 6 months after stroke suggested that basic synergistic couplings between the shoulder and elbow during a functional reaching task diminished as a function of time after stroke (van Kordelaar et al. 2013). This suggests that the ability to plan movements in advance (i.e. feedforward motor control) may improve, thereby decreasing the continuous online corrections based on proprioceptive feedback (van Kordelaar et al. 2014; Meulenbroek et al. 2001). Such corrections based on afferent information have been shown to negatively affect the smoothness of hand and finger movements (Merdler et al. 2013).
An important measure to quantify smoothness is normalized jerk. Jerk is the third time derivative of the position of a particular body part. Normalized jerk is obtained by correcting for differences in movement duration and movement distance (Caimmi et al. 2008). As high smoothness is reflected by minimal changes in position, smoothness is inversely related to normalized jerk. We have recently shown that this jerk measure decreases (i.e. smoothness increases) substantially in the first 8 weeks after stroke (van Kordelaar et al. 2014) and levels off up to 26 weeks after stroke, suggesting that jerkiness is a sensitive measure to investigate time-dependent changes in quality of motor control, particularly early after stroke. However, due to a lack of studies combining imaging techniques with kinematic analyses, the neurological mechanisms underlying the recovery of smoothness of upper limb movements are still largely unknown.
We hypothesized that elevated recruitment of secondary sensorimotor areas would be associated with jerky movements. This hypothesis was tested by investigating the association between smoothness of finger movements during a reach-to-grasp task, measured with 3D kinematics, and activation levels in sensorimotor networks of the brain during a finger flexion–extension task, measured with functional MRI (fMRI) (Buma et al. 2010). There are strong indications that the potential for neural adaptation is mainly limited to a time window of 10 weeks after stroke in which most spontaneous neurological recovery occurs (Murphy and Corbett 2009; Langhorne et al. 2011). We tested the association between brain activation and smoothness of finger movements at 6 and 29 weeks after stroke, to assess whether this association changes with time after stroke (Buma et al. 2010; van Kordelaar et al. 2014).
- Post stroke motor impairments involving force control capabilities are devastating.
- Bimanual motor synergies provide robust data on coordinating forces between hands.
- Low-force frequency patterns reveal fine motor control strategies in paretic hands.
- Analyzing both novel approaches advance understanding of post stroke force control.
Force control deficits are common dysfunctions after a stroke. This review concentrates on various force control variables associated with motor impairments and suggests new approaches to quantifying force control production and modulation. Moreover, related neurophysiological mechanisms were addressed to determine variables that affect force control capabilities. Typically, post stroke force control impairments include:
(a) decreased force magnitude and asymmetrical forces between hands,
(b) higher task error,
(c) greater force variability,
(d) increased force regularity, and
(e) greater time-lag between muscular forces.
Recent advances in force control analyses post stroke indicated less bimanual motor synergies and impaired low-force frequency structure.Brain imaging studies demonstrate possible neurophysiological mechanisms underlying force control impairments:
(a) decreased activation in motor areas of the ipsilesional hemisphere,
(b) increased activation in secondary motor areas between hemispheres,
(c) cerebellum involvement absence, and
(d) relatively greater interhemispheric inhibition from the contralesional hemisphere.
Consistent with identifying neurophysiological mechanisms, analyzing bimanual motor synergies as well as low-force frequency structure will advance our understanding of post stroke force control.
ARTICLE: Changes in brain activation in stroke patients after mental practice and physical exercise: a functional MRI study – Full Text
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.