Mapping of impaired functional connectivity during memory phases in Alzheimer's disease and its association with cortical β-amyloid

Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Background: </jats:bold>Amnesia in Alzheimer's disease (AD) could be due to disrupted encoding, consolidation dysfunction, or an impairment in the retrieval of stored memory information. The different memory phases relate with different parts of functional brain systems. <jats:bold>Methods: </jats:bold>We combine task functional magnetic resonance imaging and amyloid positron emission tomography in 72 participants (36 AD and 36 controls), to investigate the relationship between memory performance, memory phase-locked functional connectivity, and cortical β-amyloid deposition.<jats:bold>Results: </jats:bold>We found that AD was mainly characterized by decreased functional connectivity in a new data-driven Network composed of regions from default mode network, limbic network and frontoparietal network during the memory maintenance and retrieval phase. Within the Network, AD had more regions with reduced connectivity during the retrieval phase than other phases, locating mainly in the medial prefrontal cortex, posterior cingulate cortex, middle temporal and inferior parietal cortex of left hemisphere. Furthermore, functional connectivity in the Network related to memory performance. Crucially, the magnitude of the Network connectivity reduction during retrieval negatively correlated with mean cortical β-amyloid, and this relationship mediated the relationship between cortical β-amyloid and memory performance.<jats:bold>Conclusions: </jats:bold>Our findings show that memory deficiency in AD relates with decreased connectivity in specific network and cortical β-amyloid only during retrieval phase. These findings help to map impaired functional connectivity during memory phases and explain the relationship between memory deficiency and cortical β-amyloid.</jats:p>