Electroencephalogram-Based Metastability in Mild Cognitive Impairment Alzheimer's Disease

Background: The current study analyses metastability, a feature of brain dynamics in subjects experiencing mild cognitive impairment Alzheimer's disease (MCI-AD) under eyes open (EO) and eyes closed (EC) conditions. Alzheimer's disease is a critically prolonged brain disorder that alters brain connectivity through changes in neural synchronization and desynchronization. Metastable states occur when functional connectivity patterns changes as a consequence of temporal dynamics of brain. Thus, studying metastability under EO and EC would help in understanding the cortical dynamics and its impact in early-stage Alzheimer's disease. Methods: The study estimated metastability from three methods namely frequency variance analysis, Kuramoto order parameter and through meta-state activation patterns. Frequency variance estimated from 21 EEG channels were clustered into three regions namely anterior, central and posterior to study the regional metastability analysis. Global metastability was assessed from Kuramoto order parameter and meta-state activation patterns by collating the 21 EEG channels. Results: Reduction in metastability was observed in central regions of MCI-AD subjects through the study of frequency variance analysis. There was a marked reduction in global metastability in the patient group under resting EO condition. Reduction in meta-state activation properties such as TAS complexity, modularity and leap size in MCI-AD condition under EO condition indicates an overall reduction in brain flexibility. Conclusion: Taken together, the study infers an underlying structural change in neuronal dynamics influencing the reduction of metastability under MCI-AD condition. The study further revealed that this reduction in metastability is more pronounced in EO condition.