Imbalance, compensation, and rigidity in brain functional connectivity and microstates among older adults with cognitive impairment.

OBJECTIVE: This study seeks to analyze the coordinated patterns of spontaneous neural activity and instantaneous electrical activity in the brain using dual-dimensional indicators of brain functional connectivity and microstates, aiming to identify potential biomarkers for early screening and precise classification. METHODS: A case-control study design was utilized, with 195 older adults suffering from cognitive impairment (with a roughly equal distribution of mild and moderate cases) serving as the case group, and 65 healthy older adults matched as the control group. Participants were required to complete a demographic questionnaire, the Montreal Cognitive Assessment Scale, the short form of the International Physical Activity Questionnaire, and the Pittsburgh Sleep Quality Index, after which 5 min of eyes-closed resting EEG signals were recorded. RESULTS: Significant differences were observed in the average strength and density of brain functional connectivity within the δ and θ frequency bands among older adults with different cognitive levels, indicating that higher average strength and density corresponded to more severe cognitive impairment (P < 0.05). Older adults with varying cognitive levels showed significant differences in both static features (Duration, Coverage, Occurrence) and dynamic features (transition probabilities) of microstates A, B, C, and D (P < 0.05). In terms of static features, stronger temporal characteristics of microstates B and D were associated with greater severity of cognitive impairment, while microstate A demonstrated the most pronounced temporal characteristics during the mild cognitive impairment stage (P < 0.05). In dynamic features, healthy older adults primarily exhibited bidirectional balanced transitions between A/C↔C/A and B/D↔D/B, while those with mild cognitive impairment displayed transitional characteristics in the paths A→B/D and C→D. In contrast, older adults with moderate to severe cognitive impairment showed significantly enhanced directed transitions from microstates B/D to A/C (P < 0.05). CONCLUSION: Older adults with mild cognitive impairment demonstrated increased abnormal and redundant brain functional connectivity, inefficiency in microstate C, and compensatory mechanisms in low-frequency connectivity in brain functions as well as microstates A, B, and D. Older adults with moderate to severe cognitive impairment displayed sustained compensatory mechanisms in brain functional connectivity and microstates, characterized by dominant abnormal and redundant connections, along with pathological hypersynchrony in microstates B and D, which persisted until rigidity set in.