Spectral EEG characteristics during increases in the complexity of the context of cognitive activity

Abstract

The spatial and frequency characteristics of cortical electrical activity were studied in healthy human subjects in two series of experiments involving solution of sequentially presented visual tasks. The first task was to assess the relative sizes of two circles and was identical in both series. In the first series, this was supplemented by a task consisting of recognition of pseudowords/words, presumptively also requiring predominant involvement of the ventral "what?" visual system. In the second series, the additional task (spatial localization of a target stimulus in a matrix of letters) was associated with the predominant involvement of the dorsal "where?" visual system. Cortical electrical activity immediately before presentation of pairs of tasks was analyzed. Measures of EEG spectral power in the frontal, central, occipital, and temporal areas of the cortex was subjected to dispersion analysis. The power of electrical potentials in the delta and beta1 frequency ranges was greater when both tasks were associated predominantly with activation of the ventral visual system (first series of experiments). Power in the occipital alpha rhythm was lesser in the left hemisphere in both series of experiments. The interaction of the "experimental series" and "hemisphere" factors was significant in the temporal areas for EEG activity in the alpha2 range, where the predominant involvement of the ventral visual system on solution of both tasks corresponded to greater asymmetry in the electrical oscillations in the rapid alpha2 rhythm and its neighboring beta1 range with greater desynchronization (lesser power) on the left side. Thus, the nature of the ongoing activity is reflected in the spatial-frequency characteristics of the "background" electrical activity of the cortex.

Modulation of Low-Frequency EEG Rhythms under Conditions of an Activation Reaction: Dependence on Psychological Characteristics of Personality

“…Recently, however, proofs of quite another type appear. An increase in the δ SP began to be correlated with increased mental strain, readiness for adequate reactions to certain stimuli, suppression of perception of irrelevant influences, and formation of a goal for cognitive activity [17]. It should be mentioned that a rather clearly expressed δ rhythm in EEGs recorded in the state of functional resting was readily observed in most healthy adult subjects in both our own studies [12] and studies of many other authors [1].…”

“…A rise in the δ rhythm in the frontal cortex was found after receiving an instruction disposing the subject to an activity of the certain type [17]. An increase in the proportion of the δ component was observed in the course of effective processing of visual information [26].…”

Interrelations between Peculiarities of the Motivational Sphere of a Personality and Characteristics of the Current EEG

“…On the other hand, such modulation of δ oscillations can be related to the readiness for an adequate reaction to presentation of one instructiondetermined stimulus or another [12]. Intensification of δ oscillations can coincide with the acceptance of a decision for a reaction, i.e., with a stage of formation of the aim in the course of intense cognitive activity [13]. Our tests demonstrated that the intense θ-rhythm SP was manifested in the subgroups with a medium N-Ach level and high estimates of the AchM.…”

Locus of Psychological Control and Characteristics of the EEG Frequency Components

“…This effect is observed in the course of formation of behavioral automated acts and suppression of the trend toward erroneous reactions into the activating cerebral system [8]. Relatively high SPs of the δ rhythm are also related to increased mental stress, readiness for adequate reactions to certain stimuli, inhibition of perception of irrelevant influences, and formation of orientation for cognitive activity [9]. As was mentioned, a relatively high power of δ oscillations was observed in the frontal cortical regions of low-anxiety subjects after closing the eyes [10].…”