Abstract
BackgroundMotor outcome after stroke is associated with reorganisation of cortical networks and corticospinal tract (CST) integrity. However, the relationships between motor severity, CST damage, and functional brain connectivity are not well understood. Here, the main objective was to study the effect of CST damage on the relationship between functional motor network connectivity and hand motor function in two groups of stroke patients: the severely (n=8) and the mildly impaired (n=14).MethodsTwenty-two carotid stroke patients with motor deficits were studied with magnetic resonance imaging (MRI) at 3 weeks, at 3 and 6 months. Healthy subjects (n=28) were scanned once. The CST injury was assessed by fractional anisotropy values. Functional connectivity was studied from a whole-hand grip task fMRI in a cortical and cerebellar motor network. Functional connectivity indexes were computed between these regions at each time point. The relationship between hand motor strength, ipsilesional CST damage and functional connectivity from the primary motor cortex (M1) was investigated using global and partial correlations.FindingsIn mildly impaired patients, cortico-cortical connectivity was disturbed at three weeks but returned to a normal pattern after 3 months. Cortico-cerebellar connectivity was still decreased at 6 months. In severely impaired patients, the cortico-cortical connectivity tended to return to a normal pattern, but the cortico-cerebellar connectivity was totally abolished during the follow-up. In the entire group of patients, the hand motor strength was correlated to the ipsilesional functional connectivity from M1. Partial correlations revealed that these associations were not anymore significant when the impact of CST damage was removed, except for the ipsilesional M1-contralateral cerebellum connectivity.ConclusionFunctional brain connectivity changes can be observed, even in severely impaired patients with no recovery. Upper limb function is mainly explained by the CST damage and by the ipsilesional cortico-cerebellar connectivity.
Highlights
Motor outcome after stroke is associated with the cerebral reorganisation of local and remote cortical areas, leading to restore a functionally efficient motor network [1,2,3]
We further examined the partial correlation coefficients between grip strength ratio and functional connectivity indexes to remove the effect of changes due to Fractional anisotropy (FA) in the corticospinal tract (CST)
The median time delay between stroke and each of the three visits was identical in the two groups of patients (median, interquartile range (IQR) at V1: 25 (15–35) vs. 28 days (22–34), p=0.9; median, IQR at V2: 93 (89–95) vs. 88 days (83–94), p=0.9; median, IQR at V3: 233 (204–254) vs. 213 days (196–221), p=0.95, for the mildly and severely impaired groups, respectively)
Summary
Motor outcome after stroke is associated with the cerebral reorganisation of local and remote cortical areas, leading to restore a functionally efficient motor network [1,2,3]. Several longitudinal fMRI studies have described time-related changes of brain activation during the recovery of the paretic hand [4,5,6,7,8,9,10,11,12,13,14,15,16,17]. The relationship between longitudinal functional changes and CST integrity has been assessed in only a few studies [4,6,13]. The main objective was to study the effect of CST damage on the relationship between functional motor network connectivity and hand motor function in two groups of stroke patients: the severely (n=8) and the mildly impaired (n=14). Upper limb function is mainly explained by the CST damage and by the ipsilesional cortico-cerebellar connectivity
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