Reorganization of system brain activity while understanding visually presented texts with the increasing completeness of information

The characteristic features of brain activity under variation of the information regimes associated with the stages of understanding visually presented texts in adult subjects (n = 148) have been studied. An original methodology for step-by-step presentation of texts has been developed in order to “detect” the psychophysiological markers of different degrees of understanding and to identify the successive steps in this process. The following three stages were determined by spectral analysis and calculation of the fractal dimension of EEG: “before understanding,” “understanding,” and “after understanding.” The phenomenon of V-shaped changes in the values of EEG fractal dimension was discovered. The first stage is characterized by the increasing power of EEG spectrum in the high frequency range and by the enhanced fractal dimension of EEG, which probably reflects the process of idea generation and the search for solutions. At the next stage (“understanding”), the value of EEG fractal dimension decreases and the spectrum power of the low-frequency range increases, which seems to reflect simplification of invariance to the only valid alternative. The last stage is characterized by an increasing power of EEG spectrum in the high-frequency range and the increasing value of EEG fractal dimension, which may reflect the intensification of brain activity related to solution validation. The findings are a step closer to understanding the neurophysiological mechanisms of system brain activity reorganization while making sense of visually presented texts; they outline the pathway to elimination of the contradictions existing in the literature as concerns the role of high- and low-frequency EEG components as markers of the state of understanding.