Abstract
To describe structural covariance networks of gray matter volume (GMV) change in 28 patients with first-ever stroke to the primary sensorimotor cortices, and to investigate their relationship to hand function recovery and local GMV change. Tensor-based morphometry maps derived from high-resolution structural images were subject to principal component analyses to identify the networks. We calculated correlations between network expression and local GMV change, sensorimotor hand function and lesion volume. To verify which of the structural covariance networks of GMV change have a significant relationship to hand function, we performed an additional multivariate regression approach. Expression of the second network, explaining 9.1% of variance, correlated with GMV increase in the medio-dorsal (md) thalamus and hand motor skill. Patients with positive expression coefficients were distinguished by significantly higher GMV increase of this structure during stroke recovery. Significant nodes of this network were located in md thalamus, dorsolateral prefrontal cortex, and higher order sensorimotor cortices. Parameter of hand function had a unique relationship to the network and depended on an interaction between network expression and lesion volume. Inversely, network expression is limited in patients with large lesion volumes. Chronic phase of sensorimotor cortical stroke has been characterized by a large scale co-varying structural network in the ipsilesional hemisphere associated specifically with sensorimotor hand skill. Its expression is related to GMV increase of md thalamus, one constituent of the network, and correlated with the cortico-striato-thalamic loop involved in control of motor execution and higher order sensorimotor cortices. A close relation between expression of this network with degree of recovery might indicate reduced compensatory resources in the impaired subgroup.
Highlights
As both cross-sectional and a few longitudinal observational studies have demonstrated, behavioral recovery from hemiparesis after ischemic stroke shows marked between-subject variability [1, 2]
Response feature analysis (RFA) of the picking small objects (PSO) task indicated that eight patients showed normal motor performance at baseline, ten patients exponential recovery that converged to normal motor performance (“slow recovery”) and eight whose recovery trajectories followed exponential recovery curves that did not reach normal performance (“impaired recovery”) [21]
PC2TBM expression could distinguish between subgroups: When dividing patients into subgroups with positive versus negative network expression coefficients, we found that the positive subgroup has significantly higher thalamus gray matter volume (GMV) change, whereas the negative subgroup shows no significant change
Summary
As both cross-sectional and a few longitudinal observational studies have demonstrated, behavioral recovery from hemiparesis after ischemic stroke shows marked between-subject variability [1, 2]. Activation studies performed with fMRI have shown that successfully recovered subjects show almost normal cerebral patterns, exhibiting change during recovery from attention demanding controlled processing of motor performance in the subacute stage to more fluent and automatic processing in the late chronic stage [12]. This suggests recovery at the synaptic and/or neuronal level in the perilesional zone. An additional aspect of the recovery process evidenced by studies at varying stages post-stroke is the influence of the contralesional hemisphere, functionally rather supporting motor activity in the early acute phase and mainly inhibiting it in the chronic stage [16, 17]
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