Abstract
Language is an essential higher cognitive function supported by large-scale brain networks. In this study, we investigated functional connectivity changes in the left frontoparietal network (LFPN), a language-cognition related brain network in aphasic patients. We enrolled 13 aphasic patients who had undergone a stroke in the left hemisphere and age-, gender-, educational level-matched controls and analyzed the data by integrating independent component analysis (ICA) with a network connectivity analysis method. Resting state functional magnetic resonance imaging (fMRI) and clinical evaluation of language function were assessed at two stages: 1 and 2 months after stroke onset. We found reduced functional connectivity between the LFPN and the right middle frontal cortex, medial frontal cortex, and right inferior frontal cortex in aphasic patients as compared to controls. Correlation analysis showed that stronger functional connectivity between the LFPN and the right middle frontal cortex and medial frontal cortex coincided with more preserved language comprehension ability after stroke. Network connectivity analysis showed reduced LFPN connectivity as indicated by the mean network connectivity index of key regions in the LFPN of aphasic patients. The decreased LFPN connectivity in stroke patients was significantly associated with the impairment of language function in their comprehension ability. We also found significant association between recovery of comprehension ability and the mean changes in intrinsic LFPN connectivity. Our findings suggest that brain lesions may influence language comprehension by altering functional connectivity between regions and that the patterns of abnormal functional connectivity may contribute to the recovery of language deficits.
Highlights
Stroke-related aphasia is a significant clinical problem persisting in one third of acute stroke patients and one fifth of chronic stroke patients (Wade et al, 1986; Berthier, 2005)
When we compared the patients to the matched healthy controls, we found significantly reduced functional connectivity between the left frontoparietal network (LFPN) and the right middle frontal cortex, the medial frontal cortex, and the right inferior frontal cortex (Figure 4A, Table 3) in aphasic patients
The results showed a significant association between the medial frontal cortex and comprehension score (r = 0.555, P = 0.049; Figure 4B) and strong correlation between the right middle frontal cortex and comprehension score (r = 0.781, P = 0.002; Figure 4C), such that lower intrinsic functional connectivity between the LFPN and right middle frontal cortex and medial frontal cortex coincided with greater impairment of comprehension ability in aphasic patients
Summary
Stroke-related aphasia is a significant clinical problem persisting in one third of acute stroke patients and one fifth of chronic stroke patients (Wade et al, 1986; Berthier, 2005). Identifying the brain mechanisms underlying stroke-related aphasia is critical for understanding its prognosis and developing new therapeutic methods to treat it. In order to understand the influence of an individual cortical lesion, we must consider the loss of local neural function, and the lesion-induced changes in the larger network interactions in the brain. Functional segregation and integration are two major organizational principles of the human brain. An optimal brain requires a balance between local specialization and global integration of brain functional activity. Understanding connectivity within a whole network is critical both to understanding its normal function and to explaining brain recovery (Catani et al, 2005). The function of any brain region cannot be understood in isolation but only in conjunction with the regions with which it interacts (Seghier et al, 2010)
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