Functional and Structural Connectivity in a Non-Transgenic Model of Alzheimer’s Disease

Background: Alzheimer’s disease (AD) is a progressive neurodegenerative disorder marked by memory loss and cognitive decline, reflecting widespread brain dysfunction across multiple neural systems. Early detection of pathological changes is critical for enabling timely intervention, improved management, and better therapeutic outcomes. Methods: Using non-transgenic AD rats (Samaritan) and sham rats (Long–Evans), we explored structural and functional differences with multimodal MRI and multi-unit activity (MUA). Results: Diffusion tensor imaging (DTI) revealed no significant changes in mean diffusivity of water, but AD-related microstructural alterations of fractional anisotropy were confined to subcortical regions with cortical areas and white matter tracts remaining intact. We used functional MRI (fMRI) with blood oxygenation level-dependent (BOLD) contrast in rest-state (R-fMRI) and task-based (T-fMRI) paradigms. R-fMRI revealed much stronger functional connectivity in subcortical vs. cortical areas in AD rats, implicating AD-related functional changes in subcortical areas in agreement with DTI data. T-fMRI with sensory stimulation revealed reproducible fMRI responses in both groups; however, AD rats exhibited reduced BOLD response amplitude and spatial activation extent, which was accompanied by attenuated stimulus-evoked MUA responses. These suggest that attenuated evoked BOLD response reflects diminished neuronal activity in AD, rather than impaired neurovascular and/or neurometabolic coupling. Conclusions: Together these findings suggest that AD-induced anatomical and functional changes in subcortical areas are related to altered cortical responses, highlighting multimodal MRI as a sensitive tool for early AD-related brain changes.