Studying visual gnosis through EEG microstate analysis

Abstract

Objective diagnostic assessment of the human thought processes is an important issue of modern neurophysiology. The study was aimed to develop a system to analyze visual gnostic processes as a model of higher nervous function. A total of 30 people aged 30–60 having no acute disorders, exacerbations of chronic disorders or significant vision problems were examined. Electroencephalography analysis included EEG artifact removal, clustering and distinguishing specific EEG microctates according to the selected model with subsequent localization of the main source of activity, that had generated the EEG microstate, through the algorithms for solving the inverse EEG problem implemented in the sLORETA software package. When running the visual gnosis test (looking at written symbols), activity was recorded within a larger number of Brodmann areas compared to the state of relaxed wakefulness. Activity was detected within Brodmann areas 18 and 19 (11 and 45%, respectively) responsible for visual perception of images, area 39 being a part of Wernicke's area (6%), and the structures of premotor and prefrontal areas (areas 6–11) (up to 11%) (p < 0.001; Pearson's chi-squared test). Microstates defined when a subject is in a state of relaxed wakefulness or under visual load are not identical. Rather these are gauge derivatives of clustering in the context of used mathematical model. Solving the inverse EEG problem at the final stage of the study makes it possible to define the average sequences of rhythmic activity associated with realization of visual gnostic function.