Small World Index in Default Mode Network Predicts Progression from Mild Cognitive Impairment to Dementia

Area of Science:

• Neuroscience
• Medical Imaging
• Cognitive Science

Background:

• Mild cognitive impairment (MCI) is a precursor to Alzheimer's disease (AD).
• Understanding functional brain connectivity, particularly within the Default Mode Network (DMN), is crucial for predicting MCI conversion to AD.
• The Small World (SW) index quantifies the balance between brain integration and segregation.

Purpose of the Study:

• To explore EEG functional connectivity within the DMN in individuals with amnesic MCI.
• To characterize differences in DMN functional connectivity between MCI subjects who convert to AD (cMCI) and those who remain stable (sMCI).
• To investigate how DMN connectivity patterns differ between MCI patients with linguistic domain (LD) impairment versus executive domain (ED) impairment.

Main Methods:

• Electroencephalography (EEG) was used to measure functional connectivity in 59 MCI subjects.
• Subjects were classified as stable MCI (sMCI) or converted MCI (cMCI) after a four-year follow-up.
• The Small World (SW) index of the DMN was computed across different frequency bands (delta, gamma, alpha1).

Main Results:

• A significantly decreased SW index in the gamma band was observed in cMCI subjects compared to sMCI subjects.
• In cMCI with linguistic domain impairment, the SW index decreased in the delta band.
• In cMCI with executive domain impairment, the SW index decreased in delta and gamma bands and increased in the alpha1 band.

Conclusions:

• Functional alterations in the DMN's connectivity are associated with MCI progression towards Alzheimer's disease.
• These alterations may reflect abnormal brain information processing during resting state, indicative of a pre-dementia stage.
• Specific patterns of DMN connectivity changes may differentiate MCI subtypes based on cognitive domain impairment.