Associations of Cortical Activation Patterns and Integrity of Corticospinal Tract with Lower Extremity Motor Functions in Patients with Chronic Stroke: Neural Plasticity Studies
Date Issued
2012
Date
2012
Author(s)
Chen, Hsiu-I
Abstract
Study I:
Purposes: The aim of this study was to examine how the intensity and lateralization of cortical activations in the primary sensorimotor cortex (SMC), supplementary motor area (SMA), and cingulate motor area (CMA) during ankle movements correlate with motor impairment and functional mobility in patients with chronic stroke.
Methods: Functional magnetic resonance imaging (fMRI) data of cortical activations during active ankle dorsiflexion movements (0.17 Hz) were acquired using a 3 Tesla MR scanner from 15 patients (6 females and 9 males; mean age, 61.2 ± 7.6 years) with unilateral hemiplegia following stroke (mean post-onset time, 18.0 ± 15.8 months) and from 15 age-matched healthy subjects (5 males and 10 females; 61.6 ± 7.3 years). The lower extremity motor component of the Fugl-Meyer Assessment (FMALE) and the Timed “Up & Go” Test (TUGT) were used to assess motor impairment of the affected lower extremity and functional mobility of patients, respectively. The activation intensity in three paired regions of interest (ROIs)- the bilateral SMC, SMA, and CMA, were calculated by summing the t values (Σt) of voxels which t values were above the t threshold defined as 50% of the mean of the top 5% maximum t values in the corresponding homologous ROIs. The degree of lateralization of cortical activation in each pair of ROIs was calculated by using a weighted laterality index (wLI) proposed by Fernandez. An wLI value of +1 indicated absolute contralateral cortical activation during ankle movements, whereas an wLI value of -1 indicated absolute ipsilateral cortical activation. The correlations between the Σt values in bilateral SMC, SMA, and CMA, and the wLI values for each pair of SMC, SMA, and CMA with the FMALE and TUGT scores were analyzed using partial correlations, controlling for age and post-onset time.
Results: The FMALE scores showed a significant negative correlation with the Σt value of SMC of the unaffected hemisphere (r= -0.627, p= 0.022) and a trend of positive correlation with the wLI of the SMC (r= 0.500, p= 0.082), suggesting that patients with greater affected lower extremity motor impairment presented greater activation intensity in the SMC of unaffected hemisphere and smaller lateralization of SMC activation during affected ankle movements. The TUGT performance showed a significant positive correlation with the Σt value of the SMC of the affected hemisphere (r= 0.729, p= 0.005), and a trend of correlation with the Σt values of the SMC of the unaffected hemisphere (r= 0.491, p= 0.09), with those of SMA of affected and unaffected hemispheres (r= 0.509, p= 0.076 and r= 0.542, p= 0.056, respectively), and with that of the CMA of the affected hemisphere (r= 0.524, p= 0.066). Patients with poorer functional mobility demonstrated greater activation intensity in bilateral SMC, SMA, and CMA of the affected hemisphere during affected ankle movements.
Discussion and Conclusions: Results of this study revealed that different aspects of lower extremity motor functions in patients with chronic stroke were correlated with different adaptive cortical activation patterns in bilateral SMC, SMA, and CMA regions in patients with stroke. While patients’ degree of motor impairment of the affected lower extremity was primarily associated with the activation intensity and lateralization of the SMC, their functional mobility was associated with activation intensity in more widespread cortical motor regions, including bilateral SMC and SMA, and CMA of the affected hemisphere. These findings suggest that the recovery of motor impairment and functional mobility of stroke patients may depend upon functional reorganization of different brain regions.
Study II:
Purposes: The two purposes of this study were (1) to investigate the associations of the structural integrity of the corticospinal tract lower extremity motor fibers (CSTLE) and cortical activation patterns with the affected lower extremity motor functions in hemiplegic patients following chronic stroke and (2) to determine the relative contributions of the structural integrity of CSTLE and cortical activation patterns to affected lower extremity motor functions in these patients.
Methods: Eighteen hemiplegic patients with chronic stroke (7 females and 11 males; mean age, 61.0 ± 7.4 years, mean post-onset time, 16.6 ± 15.0 months) were recruited. All patients underwent clinical measures and MRI scans using a 3 Tesla MR scanner. The lower extremity motor component of the Fugl-Meyer Assessment (FMALE) and the Timed “Up & Go” Test (TUGT) was used to assess motor impairment of affected lower extremity and functional mobility, respectively. Cortical activations during active ankle dorsiflexion movements were measured using an fMRI paradigm. Cortical activation patterns were assessed by calculating absolute summation of t values ( ) above activation threshold in the primary sensorimotor cortex (SMC), supplementary motor area (SMA), and cingulate motor area (CMA) of both hemispheres, as well as the relative activation intensity in these three regions of interest (ROIs) between the two hemispheres, denoted as the weighted laterality index (wLI). The Diffusion spectrum imaging (DSI) was used to assess the structural integrity of the posterior limb of internal capsule (PLIC) segment of the CSTLE. The integrity was indicated by calculating general fractional anisotropy of the PLIC segment of the CSTLE in the affected hemisphere (GFAPLIC_AH) in absolute term and by calculating the relative GFA of the PLIC (rGAFPLIC) between bilateral hemispheres in relative term. The associations of the two clinical measures (FMALE and TUGT) and the absolute and relative DSI (GFAPLIC_AH and rGAFPLIC) and fMRI measures (Σt values of bilateral SMC, SMA, and CMA activations, as well as wLI of SMC, SMA, and CMA activations) were first analyzed using the univariate linear regression analyses, controlling for age and post-onset time. Then, the multivariate linear regression analyses were performed to determine the relative contributions of the structural integrity of CSTLE and cortical activation patterns to FMALE and TUGT.
Results: Univariate analyses showed that the FMALE score was moderately to highly correlated with two DSI measures, GFAPLIC_AH (R2= 0.392, p= 0.011) and rGFAPLIC (R2= 0.572, p= 0.001), and with two fMRI measures, Σt of SMC of the unaffected hemisphere (Σt SMC_UH) (R2= 0.619, p= 0.004) and wLISMC (R2= 0.389, p= 0.056). The TUGT performance was only strongly correlated with Σt of SMC of the affected hemisphere (Σt SMC_AH) (R2= 0.688, p= 0.004), Σt SMC_UH (R2= 0.545, p= 0.034), and Σt of CMA of the affected hemisphere (Σt CMA_AH) (R2= 0.610, p= 0.014), but not with DSI measures. Multivariate regression analyses showed that Σt SMC_UH (adjusted R2= 0.505, p= 0.004) was the only significant predictor for FMALE in the model using solely absolute DSI and fMRI measures and rGFAPLIC (adjusted R2= 0.486, p= 0.031) were the only significant predictor for FMALE in the model using solely relative DSI and fMRI measures. The Σt SMC_AH alone significantly predicted TUGT performance (adjusted R2= 0.595, p= 0.004).
Discussion and Conclusions: Results of this study suggest that relative CST structural integrity measure and absolute SMC activation intensity measure in the unaffected hemisphere are the most important independent predictors for the lower extremity motor impairment level in patients with chronic patients. On the other hand, only the absolute SMC activation intensity in affected hemisphere was an independent predictor for functional mobility performance of these patients measured by TUGT. These findings suggest that different aspects of brain plasticity following stroke may contribute differentially to different dimensions of clinical motor performance.
Subjects
lower extremity motor function
functional magnetic resonance imaging
cortical activation
weighted laterality index
Type
thesis
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