Functional MRI Study Of Post-stroke Basal Ganglia Aphasia

Objective:The broad objective of this study is to characterize the brain language areas in patients with basal ganglia aphasia using resting state functional magnetic resonance imaging(re-fMRI).A multi-modality approach is taken to identify changes of brain functions by calculating degree centrality(DC),functional connectivity(FC),regional homogeneity(ReHo)and fractional amplitude of frequency fluctuation(fALFF).Based on the results,we have hypothesized the etiology of basal ganglia aphasia,its disease progression,as well as its compensation mechanism.Method:The cohort included 12 patients(7 males and 5 females)and 17 healthy controls(9 males and 8 females).All patients were diagnosed with ischemic stroke with lesions in subcortical regions,mainly located in basal ganglia,by conventional T1WI,T2WI and FLAIR MRI.In addition,no structural damage was observed in the cortical language areas.Resting stage fMRI was performed on both patients and controls.The obtained images were pre-processed with DPASAF and analyzed using REST on the Matlab 2013a platform.The degree centrality was first calculated.Then Broca's area and Wernicke's area were selected as the region of interest(ROI)for voxel-wise functional connectivity analysis.Next,a total of 4 ROI,including Broca's area,Wernicke's area and their respective mirror areas in the right brain,were selected for ROI-wise functional connectivity analysis.The change in the functional connectivity between the patients and the controls were subsequently identified.Last,the ReHo and fALFF were measured and compared.All measurements were tested using either one-sample or two-sample t-test.The locations and peak values of clusters with statistically significant changes were reported.Results:One of the regions with significant changes in the degree centrality was located in the language area at the left temporal lobe.Both the voxel-wise and ROI-wise functional connectivity analysis suggested that the Broca's area had increased connectivity with other language areas in the left brain but decreased connectivity with regions in the right brain,including the mirror area of Broca's area and Wernicke's area.The same results were observed with the Wernicke's area.Furthermore,the functional connectivity between the language areas and the cortex associated with the visual functions increased,and the functional connectivity between the language areas and the cingulate cortex decreased.ReHo results indicated the functional homogeneity within the language areas increased.The fALFF did not have statistical difference in the language areas between the patients and the controls.However,significant change of fALFF was observed in the occipital lobe,in regions closely associated with visual functions.Conclusion:This study suggests that patients with basal ganglia aphasia may not necessarily have structural damage at the cortex associated with language functions.After the development of aphasia post-stroke,the degree of neuron activity at the language areas does not increase significantly.The most significant change between patients and controls is the functional connectivity of the language areas.The functional connectivity between language areas within the left hemisphere increases,and the functional connectivity between the left and the right hemisphere decrease.We hypothesize that the lesion at the basal ganglia induces hypoperfusion,compromising the language functions by cutting down the blood supply to the cortex.Because of the vital roles of basal ganglia in several functional loops,the lesion at the basal ganglia may reduce or even complete sever the functional connectivity between the left and right hemisphere.As a result,the brain tries to compensate by increasing the functional connectivity within the hemispheres,which further enhances the functional lateralization.