EEG microstates

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Electroencephalography (EEG) microstates are brief periods of stable spatial patterns of brain activity that typically last around 60 to 120 milliseconds and are thought to represent the basic building blocks of human information processing. EEG is a non-invasive method used to record electrical activity of the brain from the scalp. Microstates have been linked to various cognitive and neurological processes, suggesting that they may play a fundamental role in brain function.

Overview

EEG microstates are detected by analyzing the EEG signal to identify periods where the topographical distribution of the electrical potentials remains quasi-stable for a short duration. These periods are believed to correspond to the times when the brain is momentarily "resting" in a particular state of information processing. The concept of microstates challenges the traditional view of EEG as random noise, instead suggesting that these stable patterns reflect the brain's dynamic organization.

Identification

The identification of EEG microstates involves several steps, including data preprocessing, segmentation of the EEG signal into stable topographic maps, and clustering of these maps into a finite number of classes that represent different microstates. Advanced statistical methods, such as k-means clustering or the modified Kohonen Self-Organizing Map (SOM), are commonly used for this purpose.

Classification

Typically, four canonical microstates (labeled A, B, C, and D) are identified in healthy adults, although the number and characteristics of these microstates can vary depending on the methodological approach and the population being studied. Each of these microstates has been associated with different cognitive and psychological functions:

• Microstate A has been linked to attentional processes.
• Microstate B is often associated with salience processing.
• Microstate C has been related to the default mode network, involved in mind-wandering and self-referential thought.
• Microstate D is thought to be related to networks involved in the processing of auditory information.

Clinical Relevance

Research has shown that alterations in microstate parameters (such as duration, occurrence, and coverage) can be associated with various psychiatric and neurological disorders, including schizophrenia, Alzheimer's disease, and autism spectrum disorder. This suggests that EEG microstates could serve as a potential biomarker for these conditions, offering insights into their underlying neurophysiological mechanisms.

Current Research and Applications

Current research on EEG microstates is focused on further elucidating their role in both healthy brain function and in disease. Studies are exploring the relationship between microstates and other neuroimaging measures, such as functional MRI (fMRI), to better understand the neural networks underlying these states. Additionally, there is interest in developing therapeutic applications, such as neurofeedback training based on microstate analysis, to treat neurological and psychiatric conditions.

Conclusion

EEG microstates represent a promising area of research that bridges the gap between neurophysiological processes and cognitive functions. By providing a window into the dynamic organization of the brain, microstate analysis has the potential to enhance our understanding of brain function in health and disease, offering new avenues for diagnosis and treatment.