Functional degeneration in dorsal and ventral attention systems in amnestic mild cognitive impairment and Alzheimer's disease: an fMRI study.

Attention deficits in patients with amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD) have already been previously proposed. However, previous studies lacked systematic comparisons on multiple phases of disease progression. In this work, we compared spontaneous functional connectivity in dorsal and ventral attention networks (DAN, VAN) in patients with aMCI and AD. Additionally, we performed a behavioral test-attention network test (ANT) which examined three attention performances: alerting, orienting, and executive control. One-way analysis of variance revealed significant group-differed functional connectivity in both networks. Specifically, functional connectivity with the dorsal seed differed in left lateralized fronto-parietal area and medial dorsal frontal cortex and posterior cingulate cortex, whereas functional connectivity with the ventral seed differed in right ventral and dorsal frontal cortex. For patients with AD, both attention networks showed decreased functional connectivity in regions of interest comparisons. Accordingly, the behavioral results showed bad performance in three attention functions. These findings suggested impaired functional anatomy for top-down and bottom-up processing in AD patients. Whereas for patients with aMCI, attention systems degenerated in a selective way, specifically, with decreased functional connectivity in DAN, but preserved or enhanced one in VAN. Additionally, patients with aMCI showed selective attention deficits with preserved alerting and orienting performance but impaired executive control performance, suggesting an impaired functional anatomy for top-down processing, while preserved functional architecture for bottom-up performance. The findings indicated that diverse extent and onset of functional degenerations in dorsal and ventral attention systems as the disease severity progressed. This might provide more evidence to distinguish aMCI which would easily progress to AD.