Default Mode Network Complexity and Cognitive Decline in Mild Alzheimer's Disease

Area of Science:

• Neuroscience
• Cognitive Science
• Biomedical Engineering

Background:

• The default mode network (DMN) is crucial for self-referential cognition and mental health.
• Disruptions in DMN functional connectivity are observed in Alzheimer's disease (AD).
• Early AD may present subtle physiological changes not detected by functional connectivity alone.

Purpose of the Study:

• To investigate alterations in DMN functional connectivity and multi-scale entropy (MSE) in mild AD.
• To assess the association between MSE, functional connectivity, and cognitive function (MMSE) in AD.
• To explore MSE as a sensitive marker for early cognitive decline in AD.

Main Methods:

• Compared DMN functional connectivity and MSE in 15 mild AD patients and 14 controls.
• Utilized blood-oxygen level dependent (BOLD) signal complexity analysis (MSE) and functional connectivity measures.
• Assessed correlations between MSE, functional connectivity, and Mini-Mental State Examination (MMSE) scores.

Main Results:

• Mild AD showed reduced DMN functional connectivity between posterior cingulate cortex and right hippocampus, but not whole-network.
• The AD group exhibited significantly lower global DMN-MSE, particularly in the hippocampi.
• MSE positively correlated with functional connectivity and MMSE scores in AD patients, with right hippocampal MSE linked to semantic memory.

Conclusions:

• Decreased signal complexity (MSE) in DMN nodes reflects cognitive decline in AD.
• Altered MSE suggests impaired local information processing and inter-regional communication in AD.
• Loss of nodal signal complexity may precede and contribute to functional connectivity disruptions in AD, positioning MSE as a sensitive biomarker.