Blood oxygenation-level dependent functional MRI in evaluating the selective activation of motor cortexes associated with recovery of motor function in hemiplegic patients with ischemic stroke

INTRODUCTION Ischemic stroke can result in disability for a long time or all the life, and the major one is the hemiplegia in limbs, systematic and individu- alized rehabilitative treatment at early period is good for the early functional recovery, and ca…     

Executive functions with different motor outputs in somatosensory Go/Nogo tasks: an event-related functional MRI study

The aim of this event-related functional magnetic resonance imaging (fMRI) study was to investigate and compare executive functions with different motor outputs in somatosensory Go/Nogo tasks: (1) Button press and (2) Count. Go and Nogo stimuli were presented with an even probability. We observed a common network for Movement and Count Go trials in several regions of the brain including the dorsolateral (DLPFC) and ventrolateral prefrontal cortices (VLPFC), supplementary motor area (SMA), posterior parietal cortex (PPC), inferior parietal lobule (IPL), Insula, and superior temporal gyrus (STG). Direct comparison revealed that primary sensorimotor area (SMI), premotor area (PM), and anterior cingulate cortex (ACC) were more activated during Movement than Count Go trials. In contrast, the VLPFC was more activated during Count than Movement Go trials. Our results suggest that there were two neural networks for the supramodal executive function, common and uncommon, depending on the required response mode.     

Interconnected large-scale systems for three fundamental cognitive tasks revealed by functional MRI

The specific brain areas required to execute each of three fundamental cognitive tasks - object naming, same-different discrimination, and integer computation - are determined by whole-brain functional magnetic resonance imaging (fMRI) using a novel technique optimized for the isolation of neurocognitive systems. This technique (1) conjoins the activity associated with identical or nearly identical tasks performed in multiple sensory modalities (conjunction) and (2) isolates the activity conserved across multiple subjects (conservation). Cortical regions isolated by this technique are, thus, presumed associated with cognitive functions that are both distinguished from primary sensory processes and from individual differences. The object-naming system consisted of four brain areas: left inferior frontal gyrus, Brodmann's areas (BAs) 45 and 44; left superior temporal gyrus, BA 22; and left medial frontal gyrus, BA 6. The same-different discrimination system consisted of three brain areas: right inferior parietal lobule, BA 40; right precentral gyrus, BA 6; and left medial frontal gyrus, BA 6. The integer computation system consisted of five brain areas: right middle frontal gyrus, BA 6; right precentral gyrus, BA 6; left inferior parietal lobule, BA 40; left inferior frontal gyrus, BA 44; and left medial frontal gyrus, BA 6. All three neurocognitive systems shared one common cortical region, the left medial frontal gyrus, the object-naming and integer computation systems shared the left inferior frontal gyrus, and the integer computation and same-different discrimination systems shared the right precentral gyrus. These results are consistent with connectionist models of cognitive processes where specific sets of remote brain areas are assumed to be transiently bound together as functional units to enable these functions, and further suggest a superorganization of neurocognitive systems where single brain areas serve as elements of multiple functional systems.     

The functional anatomy of motor recovery after stroke in humans: a study with positron emission tomography

We have studied regional cerebral blood flow changes in 6 patients after their recovery from a first hemiplegic stroke. All had a single well-defined hemispheric lesion and at least a brachial monoparesis that subsequently recovered. Each patient had 6 measurements of cerebral blood flow by positron tomography with 2 scans at rest, 2 during movement of fingers of the recovered hand, and 2 during movement of fingers of the normal hand. When the normal fingers were moved, regional cerebral blood flow increased significantly in contralateral primary sensorimotor cortex and in the ipsilateral cerebellar hemisphere. When the fingers of the recovered hand were moved, significant regional cerebral blood flow increases were observed in both contralateral and ipsilateral primary sensorimotor cortex and in both cerebellar hemispheres. Other regions, namely, insula, inferior parietal, and premotor cortex, were also bilaterally activated with movement of the recovered hand. We have also demonstrated, by using a new technique of image analysis, different functional connections between the thalamic nuclei and specific cortical and cerebellar regions during these movements. Our results suggest that ipsilateral motor pathways may play a role in the recovery of motor function after ischemic stroke.     

Effect of socioeconomic status on functional and motor recovery after stroke: a European multicentre study

Background

Previous studies have shown an inverse gradient in socioeconomic status for disability after stroke. However, no distinction has been made between the period in the stroke rehabilitation unit (SRU) and the period after discharge. The purpose of this study was to examine the impact of education and equivalent income on motor and functional recovery for both periods.

Methods

419 consecutive patients were recruited from six SRUs across Europe. The Barthel Index (BI) and Rivermead Motor Assessment (RMA) were measured on admission, at discharge and 6 months after stroke. Ordinal logistic regression models were used, adjusting for case mix. Cumulative odds ratios (OR) were calculated to measure differences in recovery between educational levels and income groups with adjustments for case mix.

Results

Patients with a low educational level were less likely to improve on the BI (OR 0.53; 95% CI 0.32 to 0.87) and the RMA arm during inpatient stay (OR 0.54; 95% CI 0.31 to 0.94). For this period, no differences in recovery were found between income groups. After discharge, patients with a low equivalent income were less likely to improve on all three sections of the RMA: gross function (OR 0.20; 95% CI 0.06 to 0.66), leg and trunk (OR 0.22; 95% CI 0.09 to 0.55) and arm (OR 0.30; 95% CI 0.10 to 0.87). No differences were found for education.

Conclusions

During inpatient rehabilitation, educational level was a determinant of recovery, while after discharge, equivalent income played an important role. This study suggests that it is important to develop a better understanding of how socioeconomic factors affect the recovery of stroke patients.Socioeconomic health inequalities have been studied for a long time but the publication of the Black Report¹ in the UK provoked the attention of policy makers for the existence of important health inequalities² and resulted in an increased awareness of these issues in health care in general.³ At the end of the 20th century, some authors even considered socioeconomic health disparities as the most important public health issue.⁴Stroke is no exception to the general findings on health inequalities. The incidence of fatal and non‐fatal strokes shows an inverse gradient over socioeconomic groups. In an unselected population based sample, Thrift and colleagues⁵ found that the incidence rate of both stroke types was higher in disadvantaged areas. These disparities remain in the post‐acute period. The proportion of patients who are dependent or dead at 6 months after stroke varies between groups of different socioeconomic status (SES). Patients with a lower SES are at greater risk for stroke morbidity and stroke mortality compared with higher SES groups.^6,7 However, these associations were not confirmed by other studies.^8,9 In a recent review by Cox and colleagues¹⁰ it was concluded that the association between SES and morbidity and mortality is well known but that the reasons behind this association are far from clear.The socioeconomic gradient in disability after stroke is also observed in the chronic phase. Patients with lower SES experienced more disabilities up to 3 years post‐stroke compared with the group of patients with a higher SES.¹¹ It remains unclear whether these differences are the result of differences in stroke severity at onset or whether they become more prominent over time.Comparison of results between studies may be difficult because of the different methods used to define SES. Several indicators are used to determine SES (eg, education, income). Various models are used explaining health inequalities, and education and income reflect different dimensions of socioeconomic inequalities in health.¹² The behavioural/cultural explanation is perhaps the most widely used.¹³ This model refers to the more systematic unhealthy behaviours and lifestyle in lower socioeconomic groups, in part related to differences in knowledge or awareness of risks. In this model, distinction between SES groups is often based on educational attainment.¹³ The materialist model tries to explain differences in health between SES groups by material factors (eg, housing, work conditions), and income is mainly used as an indicator for material stratification.¹⁴Apart from the choice of SES indicator, differences in how the selected indicator is measured may hamper comparison between studies and make general conclusions more difficult. For example, the measurement of an indicator can be based on an individual level or at a more aggregated area level. Although individual based indicators are preferred,¹⁵ the availability of data is probably an underestimated factor in how indicators are measured.As most functional recovery is expected to take place in the first 5 months after stroke,¹⁶ stroke rehabilitation units (SRUs) may play an important role in minimising discrepancies between socioeconomic groups. However, the influence of SES on recovery during inpatient stay has not been studied. Moreover, illness trajectories are not often considered in the comparison of functional recovery between socioeconomic groups.¹⁷ To the best of our knowledge, no distinction has been made between recovery during stay in an inpatient SRU and after discharge for different SES groups. Therefore, the aim of this study was to assess the association of education and equivalent income with functional and motor recovery for these two periods.     

Relating MRI changes to motor deficit after ischemic stroke by segmentation of functional motor pathways

BACKGROUND AND PURPOSE: Infarct size on T2-weighted MRI correlates only modestly with outcome, particularly for small strokes. This may be largely because of differences in the locations of infarcts and consequently in the functional pathways that are damaged. To test this hypothesis quantitatively, we developed a "mask" of the corticospinal pathway to determine whether the extent of stroke intersection with the pathway would be more closely related to clinical motor deficit and axonal injury in the descending motor pathways than total stroke lesion volume. METHODS: Eighteen patients were studied > or =1 month after first ischemic stroke that caused a motor deficit by use of brain T2-weighted imaging, MR spectroscopic (MRS) measurements of the neuronal marker compound N-acetyl aspartate in the posterior limb of the internal capsule, and motor impairment and disability measures. A corticospinal mask based on neuroanatomic landmarks was generated from a subset of the MRI data. The maximum proportion of the cross-sectional area of this mask occupied by stroke was determined for each patient after all brain images were transformed into a common stereotaxic brain space. RESULTS: There was a significant linear relationship between the maximum proportional cross-sectional area of the corticospinal mask occupied by stroke and motor deficit (r(2)=0.82, P<0.001), whereas the relationship between the total stroke volume and motor deficit was better described by a cubic curve (r(2)=0.76, P<0.001). Inspection of the data plots showed that the total stroke volume discriminated poorly between smaller strokes with regard to the extent of associated motor deficit, whereas the maximum proportion of the mask cross-sectional area occupied by stroke appeared to be a more discriminatory marker of motor deficit and also N-acetyl aspartate reduction. CONCLUSIONS: Segmentation of functional motor pathways on MRI allows estimation of the extent of damage specifically to that pathway by the stroke lesion. The extent of stroke intersection with the motor pathways was more linearly related to the magnitude of motor deficit than total lesion volume and appeared to be a better discriminator between small strokes with regard to motor deficit. This emphasizes the importance of the anatomic relationship of the infarct to local structures in determining functional impairment. Prospective studies are necessary to assess whether this approach would allow improved early estimation of prognosis after stroke.     

Changes of cortico-cortical neural connections associated with motor functional recovery after stroke

ObjectivesDuring functional recovery after stroke, some neural connections in the brain are augmented and new neural networks are constructed to compensate for impaired neurological functions. Recently, it was reported that the extent of cortico-cortical neural connections can be estimated by correlation analysis based on electroencephalography (EEG). The purpose of this study was to investigate changes of correlation coefficients in the cerebral cortex with motor functional recovery after stroke.Materials and methodsTwenty-two post-stroke hemiparetic patients admitted to our rehabilitation ward (mean age at admission: 71.4 ± 12.9 years old), were studied. For the evaluation of hemiparesis, Fugl-Meyer Assessment (FMA) was applied. All subjects underwent EEG with electrodes placed according to the international 10-20 system for correlation analysis, on admission to our ward and 4 weeks after admission. EEG data were analyzed with the program software FOCUS (NIHON KOHDEN, Japan), and squared correlation coefficients in some cortico-cortical areas of the cerebral cortex were calculated.ResultsThe correlation coefficients in some cortico-cortical areas of the lesional hemisphere, such as C3-F3 or C4-F4, C3-F7 or C4-F8, and F3-F7 or F4-F8, significantly increased with rehabilitation training. The change of the correlation coefficient in F3-F7 or F4-F8 and F7-T3 or F8-T4 in the lesional hemisphere was significantly correlated with the change of the upper-limb FMA.ConclusionsThe augmentation of cortico-cortical connections, represented by an increase of the correlation coefficient in the lesional hemisphere, may contribute to motor functional recovery, especially in hemiparetic upper limbs, after stroke.     

Imaging motor recovery after stroke

Most patients show improvement in the weeks or months after a stroke. Recovery is incomplete, however, leaving most with significant impairment and disability. Because the brain does not grow back to an appreciable extent, this recovery occurs on the basis of change in function of surviving tissues. Brain mapping studies have characterized a number of processes and principles relevant to recovery from stroke in humans. The findings have potential application to improving therapeutics that aim to restore function after stroke.     

A review of motor recovery mechanisms in patients with stroke

Elucidation of the motor recovery mechanisms in stroke patients is important because such information could provide the scientific basis for stroke rehabilitation. The motor recovery mechanism after stroke, however, has not yet been clearly elucidated, but several suggested mechanisms have been proposed. These include the ipsilateral motor pathway from the unaffected motor cortex to the affected hand, peri-lesional reorganization, the recovery of a damaged lateral corticospinal tract, and contribution of the secondary motor area. Additionally, little is known about the motor recovery mechanism for patients with intracerebral hemorrhage, for locomotor recovery, and for damage at the subcortical level. Therefore, we suggest that further research should be focused on the elucidation of motor recovery mechanisms in relation to the above topics. In the current study, we tried to review the literatures about the motor recovery mechanisms of the patients with stroke.     

Manganese-enhanced MRI of brain plasticity in relation to functional recovery after experimental stroke.

Restoration of function after stroke may be associated with structural remodeling of neuronal connections outside the infarcted area. However, the spatiotemporal profile of poststroke alterations in neuroanatomical connectivity in relation to functional recovery is still largely unknown. We performed in vivo magnetic resonance imaging (MRI)-based neuronal tract tracing with manganese in combination with immunohistochemical detection of the neuronal tracer wheat-germ agglutinin horseradish peroxidase (WGA-HRP), to assess changes in intra- and interhemispheric sensorimotor network connections from 2 to 10 weeks after unilateral stroke in rats. In addition, functional recovery was measured by repetitive behavioral testing. Four days after tracer injection in perilesional sensorimotor cortex, manganese enhancement and WGA-HRP staining were decreased in subcortical areas of the ipsilateral sensorimotor network at 2 weeks after stroke, which was restored at later time points. At 4 to 10 weeks after stroke, we detected significantly increased manganese enhancement in the contralateral hemisphere. Behaviorally, sensorimotor functions were initially disturbed but subsequently recovered and plateaued 17 days after stroke. This study shows that manganese-enhanced MRI can provide unique in vivo information on the spatiotemporal pattern of neuroanatomical plasticity after stroke. Our data suggest that the plateau stage of functional recovery is associated with restoration of ipsilateral sensorimotor pathways and enhanced interhemispheric connectivity.     

An event-related functional MRI study comparing interference effects in the Simon and Stroop tasks

The Stroop and Simon tasks typify a class of interference effects in which the introduction of task-irrelevant stimulus characteristics robustly slows reaction times. Behavioral studies have not succeeded in determining whether the neural basis for the resolution of these interference effects during successful task performance is similar or different across tasks. Event-related functional magnetic resonance imaging (fMRI) studies were obtained in 10 healthy young adults during performance of the Stroop and Simon tasks. Activation during the Stroop task replicated findings from two earlier fMRI studies. These activations were remarkably similar to those observed during the Simon task, and included anterior cingulate, supplementary motor, visual association, inferior temporal, inferior parietal, inferior frontal, and dorsolateral prefrontal cortices, as well as the caudate nuclei. The time courses of activation were also similar across tasks. Resolution of interference effects in the Simon and Stroop tasks engage similar brain regions, and with a similar time course. Therefore, despite the widely differing stimulus characteristics employed by these tasks, the neural systems that subserve successful task performance are likely to be similar as well.     

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.     

Hand motor recovery after stroke: a transcranial magnetic stimulation mapping study of motor output areas and their relation to functional status

The respective contributions of the stroke and undamaged hemispheres to motor recovery after stroke remains controversial. The aim of this article is to evaluate the relationship between location and size of cortical motor areas and outcome after stroke. Twelve controls and 12 stroke patients were studied. Hand cortical motor output areas were determined using transcranial magnetic stimulation. Motor-evoked potentials were recorded simultaneouslyfrom both hands. Functional motor abilities were evaluated using well-validated measures. Surface area, weighted surface area, and center of gravity of motor output areas were calculated. Different patterns of motor output areas to the paretic band were observed; there was no motor output from the stroke hemisphere in patients with poor outcome, contrasting to large motor output area in the stroke hemisphere in patients with good outcome, regardless of infarct size or location. A significant correlation was found between measures of motor outcome in the stroke-affected upper extremity and both the surface area and weight of the central motor output area in the stroke hemisphere. No ipsilateral motor response was obtained after stimulation of either hemisphere. These data support an association between preservation of cortical motor output area to the paretic hand in the stroke hemisphere and good motor outcome.     

Cortico-spinal excitability and hand motor recovery in stroke: a longitudinal study

Objective

To describe the relationship between changes of cortico-spinal excitability and motor recovery of the affected hand after stroke.

Methods

Eighteen hemiparetic stroke patients with a severe-to-mild upper limb motor impairment were randomized. Cortico-spinal excitability measures (resting motor thresholds and motor evoked potentials) obtained from a distal (abductor pollicis brevis) and proximal (biceps brachii) upper limb muscle were assessed for both hemispheres. Motor function of the affected hand was tested by the Wolf Motor Function and Action Research Arm tests. The evaluations were performed at baseline and weekly over 7 weeks of in-patient neurological rehabilitation.

Results

Severe hand dysfunction was associated with a strong suppression of ipsilesional cortico-spinal excitability and a shift of excitability towards the contralesional hemisphere. Mild hand impairment was associated with a shift of cortico-spinal excitability towards the ipsilesional hemisphere. Favorable motor recovery correlated with an increase of ipsilesional cortico-spinal excitability.