Visuospatial processing in early Alzheimer's disease: a multimodal neuroimaging study

Area of Science:

• Neuroscience
• Cognitive Neurology
• Neuroimaging

Background:

• Dorsal pathway dysfunction is linked to visuospatial deficits in Alzheimer disease (AD).
• Prior research suggests compensatory mechanisms in dorsal or ventral pathways.
• Functional and structural connectivity changes may indicate pathway disconnection.

Purpose of the Study:

• To investigate functional alterations in the dorsal pathway in mild cognitive impairment (MCI), a prodromal stage of AD.
• To combine functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) to explore brain activity and structural connectivity.
• To understand the relationship between functional reorganization and structural changes in MCI.

Main Methods:

• Recruited 18 male individuals with amnestic MCI (aMCI) and 18 age- and education-matched healthy controls.
• Utilized fMRI during an object recognition task, comparing responses to non-canonical versus canonical object orientations.
• Applied DTI to investigate structural connectivity in regions with observed functional differences.

Main Results:

• Patients with aMCI exhibited increased frontal, temporal, and parietal activation when recognizing non-canonical objects.
• Less deactivation in areas with decreased diffusion and increased activation in areas with increased diffusion were observed in aMCI patients.
• Decreased diffusion in the hippocampal cingulum, a pathway connecting dorsal and ventral regions, was found in aMCI patients.

Conclusions:

• Increased activation in both ventral and dorsal pathways suggests functional reorganization in early AD.
• Decreased deactivation and diffusion indicate functional reorganization, while increased activation and diffusion suggest compensatory processes.
• This study provides the first structural evidence of functional reorganization in MCI, potentially linked to cingulum connectivity loss.