On the intercorrelation of some frequency and amplitude parameters of the human EEG and its functional significance. Communication I: Multidimensional neurodynamic organization of functional states of the brain during intellectual, perceptive and motor activity in normal subjects

In 95 normal subjects, a separate evaluation of the amplitude and frequency parameters of EEG by period analysis made it possible to reveal, using factor analysis, four independent groups of parameters — the EEG factors, two of which being independent of the amplitude fluctuations. They were considered as integral EEG characteristics of qualitatively different neurophysiological processes. Decrease of Factor I values during mental activity (called `general activation') reflected an intercorrelated desynchronization of the wave amplitudes in all the bands, a decrease of α-index (percentage presence in epoch) and regularity together with parallel increase of the indices and mean periods of Δ- and θ-waves. This generalized reaction has shown `non-specific' dependence upon novelty and difficulty of the tasks and stimuli with certain task-specific topographical distribution. An increase of values of regional Factor Ia in the anterior areas was caused by Δ- and θ-amplitude synchronization, more pronounced during matching the rhymes (MR) than in mental multiplication (MM). An increase of Factor II values (related to increase of the index, frequency and regularity of β-activity and called `cortical excitation' , CE) was more expressed during MR, whereas an increase of Factor III values (an increase of mean α-period and θ-index called `active selective inhibition', ASI) was characteristic of MM, the latter reaction being evident in the right hemisphere. During analysis of external sound stimuli and rhythmical clenching of a fist, an increase of Factor III values was accompanied by decrease of Factor II values in the motor activity; such reciprocal reaction being localized in the central areas contralateral to the hand moved. Neuropsychological analysis suggests that CE correlates with associative and successively organized mental operations involving search for memory traces and ASI presumably relates to different aspects of mental selectivity such as simultaneous mental operations, voluntary attention and mental automation, the latter two cases being supported by parallel reduction of CE.