Altered EEG microstate dynamics in mild cognitive impairment and Alzheimer's disease.

Objective: Resting-state EEG microstate is a promising neurophysiological tool to explore the temporal dynamics of cognitive activity. Till now, the microstate syntax is far from being fully understood in mild cognitive impairment (MCI) and Alzheimer's disease (AD). We aim to investigate the possible explanation for the alterations of transition probabilities in microstate syntax between different stages of cognitive impairment.

Methods: The artefact-corrected resting-state EEG in patients with MCI (n = 46), AD (n = 43) and healthy controls (HC, n = 43) were used for microstate analysis. Four microstates were labeled A-D according to the study (Koenig et al., 2002).

Results: Microstate duration, occurrence and coverage showed overall differences between HC, MCI and AD. Duration and coverage B increased significantly in AD compared with HC and MCI. Coverage C decreased significantly in AD compared with MCI. Microstate syntax had specialized single transitions in MCI and AD. Transitions between symmetrical (C and D) and asymmetrical (A and B) classes showed a decreased pattern. It was only in MCI that an increased transition from A to C was found and only in AD an increased transition from A to B was found. Besides, a negative spearman's correlation was found between the transition probability from A to B and Mini-Mental State Examination (MMSE) scores.

Conclusion: Altered resting-state EEG microstates in particular specialized single transitions in microstate syntax were showed in MCI and AD.

Significance: For the first time, we discovered which single transitions between pairs of microstates play an important role in microstate syntax in different stages of cognitive impairment.