Abstract
Brain lesions caused by cerebral ischemia lead to network disturbances in both hemispheres, causing a subsequent reorganization of functional connectivity both locally and remotely with respect to the injury. Quantitative electroencephalography (qEEG) methods have long been used for exploring brain electrical activity and functional connectivity modifications after stroke. However, results obtained so far are not univocal. Here, we used basic and advanced EEG methods to characterize how brain activity and functional connectivity change after stroke. Thirty-three unilateral post stroke patients in the sub-acute phase and ten neurologically intact age-matched right-handed subjects were enrolled. Patients were subdivided into two groups based on lesion location: cortico-subcortical (CS, n = 18) and subcortical (S, n = 15), respectively. Stroke patients were evaluated in the period ranging from 45 days since the acute event (T0) up to 3 months after stroke (T1) with both neurophysiological (resting state EEG) and clinical assessment (Barthel Index, BI) measures, while healthy subjects were evaluated once. Brain power at T0 was similar between the two groups of patients in all frequency bands considered (δ, θ, α, and β). However, evolution of θ-band power over time was different, with a normalization only in the CS group. Instead, average connectivity and specific network measures (Integration, Segregation, and Small-worldness) in the β-band at T0 were significantly different between the two groups. The connectivity and network measures at T0 also appear to have a predictive role in functional recovery (BI T1-T0), again group-dependent. The results obtained in this study showed that connectivity measures and correlations between EEG features and recovery depend on lesion location. These data, if confirmed in further studies, on the one hand could explain the heterogeneity of results so far observed in previous studies, on the other hand they could be used by researchers as biomarkers predicting spontaneous recovery, to select homogenous groups of patients for the inclusion in clinical trials.
Highlights
Stroke is a leading cause of severe long-term disability in both the United States (Benjamin et al, 2018) and Europe1.Ischemic stroke damages the brain tissue in the affected vascular territories, inducing a corresponding loss of function
The results obtained in this study demonstrated that brain electrical activity and connectivity are significantly modified by a stroke event, and such modifications depend on lesion location
Analysis of brain power computed from regions of interest (ROIs) revealed that baseline clinical status (BI T0) and low-frequency oscillations in stroke patients show an opposite correlation depending on lesion location
Summary
Stroke is a leading cause of severe long-term disability in both the United States (Benjamin et al, 2018) and Europe (source)1.Ischemic stroke damages the brain tissue in the affected vascular territories, inducing a corresponding loss of function. A relationship between interhemispheric activity balance and functional recovery was demonstrated (van Putten, 2007; Agius Anastasi et al, 2017) and a different involvement of the affected and unaffected hemispheres (AH and UH, respectively) in different post-stroke phases was highlighted (Murase et al, 2004; Sheorajpanday et al, 2011). In this regard, recent studies have described a specific brain reorganization in the UH that tends to interact with functional recovery in patients in the early post stroke stage (Van Kaam et al, 2018). The UH appears to be involved in a continuous support function even long after the injury (Lotze et al, 2006; Riecker et al, 2010; Finnigan and van Putten, 2013)
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