Disruptions of the olfactory and default mode networks in Alzheimer's disease

• Published in: Brain and behavior Vol. 9; no. 7; pp. e01296 - n/a
• Main Authors: Lu, Jiaming, Yang, Qing X., Zhang, Han, Eslinger, Paul J., Zhang, Xin, Wu, Sichu, Zhang, Bing, Zhu, Bin, Karunanayaka, Prasanna R.
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 01.07.2019; John Wiley and Sons Inc; Wiley
• Subjects: Age; Aged; Alzheimer Disease - physiopathology; Alzheimer Disease - psychology; Alzheimer's disease; Atrophy; Behavior; Brain research; Cognition - physiology; Correlation of Data; default mode network; Dementia; Female; Humans; Identification; Magnetic Resonance Imaging - methods; Male; Memory; Memory - physiology; mild cognitive impairment; Nerve Net - diagnostic imaging; Nerve Net - physiopathology; Neurodegeneration; NMR; Nuclear magnetic resonance; Olfactory Cortex - diagnostic imaging; Olfactory Cortex - physiopathology; olfactory fMRI; olfactory network; Olfactory Perception - physiology; Original Research; Pathology; United States > US; Pennsylvania; mild cognitive impairment; default mode network; olfactory network; Alzheimer's disease; olfactory fMRI
• ISSN: 2162-3279; 2162-3279
• DOI: 10.1002/brb3.1296

Introduction Olfactory deficits are prevalent in early Alzheimer's disease (AD) and are predictive of progressive memory loss and dementia. However, direct neural evidence to relate AD neurodegeneration to deficits in olfaction and memory is limited. Methods We combined the University of Pennsylvania Smell Identification Test (UPSIT) with olfactory functional magnetic resonance imaging (fMRI) to investigate links between neurodegeneration, the olfactory network (ON) and the default mode network (DMN) in AD. Results Behaviorally, olfactory and memory scores showed a strong positive correlation in the study cohorts. During olfactory fMRI, the ON showed reduced task‐related activation and the DMN showed reduced task‐related suppression in mild cognitive impairment (MCI) and AD subjects compared to age‐matched cognitively normal subjects. Conclusions The results provide in vivo evidence for selective vulnerability of ON and DMN in AD and significantly improves the viable clinical applications of olfactory testing. A network‐based approach, focusing on network integrity rather than focal pathology, seems beneficial to olfactory prediction of dementia in AD. Olfactory and memory scores can differentiate Alzheimer's disease (AD) from mild cognitive impairment (MCI). Neurodegeneration, as measured by hippocampus and primary olfactory cortex (POC) volume is similar in AD and MCI. Patterns of ON activation support compensatory mechanisms in MCI and not in AD. DMN suppression during olfactory processing is impaired in AD. Effective connectivity between DMN and ON, in a model of causal influence, is impaired in AD.