Regional Variation in Interhemispheric Functional Connectivity (IFC) for Different Types of Dementia: A Resting State fMRI Study

Abstract

PURPOSE: To explore Interhemispheric functional connectivity (IFC) in patients of Alzheimer's disease (AD), Mixed Dementia (MD), Vascular Dementia (VD) and Subjective Cognitive Decline (SCD) based on Default Mode Network (DMN), Salience Network (SN) and Executive Control Network (ECN) with Heathy control (HC). The IFC was analyzed using voxel-mirrored homotopic connectivity (VMHC). METHOD AND MATERIALS: 75 participants (25 HC, 21 AD, 6 MD, 18 VD and 6 SCD) were recruited to undergo MRI scanning using Siemens 3T scanner. All participants were asked to remain quiet and relax during the scan, with their eyes closed but not to fall asleep. Resting state functional images were acquired using echo-planning imaging (EPI) technique. The fMRI images were preprocessed by SPM12 with Mathlab 2018a. It included elimination of the first 10 time points, slice timing correction and head motion correction. For VMHC, we adopted the method of calculation used by Kelly et al 2011 and Zuo et al 2010. VMHC map was obtained. T-test was performed by SPSS (v.25.0) to compare each group with HC. RESULTS: AD group showed significant lower VMHC values in DMN (T=-2.48 to -3.49, p<0.05) than that of HC. For SCD group showed significant higher VMHC values in SN (T=+2.68 to +4.336, P<0.05) and ECN (T=+2.537 to +3.203, P<0.05) than HC. For MD, significant higher VMHC values was found in SN (T=+2.743 to +4.464, p<0.05) but lower VMHC values in other networks (T=-2.989 at mid temporal gyrus to -4.487 at lateral occipital cortex, p<0.05). For VD group, VMHC values was significantly lower in DMN (T= -2.942 to -3.065, p<0.05) than that of HC, while having higher VMHC values in ECN (T=+2.502 to +3.540, P<0.05). CONCLUSION: Resting state fMRI showed different patterns in interhemispheric functional connectivity for AD, VD, MD, and SCD groups when comparing to HC group based on the DMN, SN, and ECN. Consistent with other studies, AD showed decreased IFC in all three networks. While for VD and MD, coexistence of decreased and increased IFC among three networks. The result suggested that recruitment of other brain regions as adaptations to compensate for the reduced IFC. CLINICAL RELEVANCE/APPLICATION: Characterization of different types of dementia, including AD, MD, VD and SCD by IFC using resting state fMRI. Resting state fMRI can be a non-invasive tool for early diagnosis of dementia