V. I. Davydov

Properties of spreading depression identified by EEG spectral analysis in conscious rabbits

Reflection of cortical waves of spreading depression in changes in high-frequency gamma activity was shown to improve significantly in conditions of bipolar recording of brain electrical activity. Intense suppression of the EEG gamma range (37–47 Hz) was seen in all cortical areas studied at the moment of onset of waves of spreading depression. The drop in the power of EEG gamma activity had clear leading and trailing fronts, allowing the passage time of the wave to be evaluated in each cortical area, as well as the sequence of propagation. Waves of spreading depression were characterized by normal, i.e., sequential movements across the cortex, only in the first 3–4 experiments. When experiments were continued, there were changes in the latent period and distortions of the propagation sequence. In some cases, waves of spreading depression responded to standard injections of KCl by developing rapidly (0.5–2 min) over the whole of the dorsal surface of the neocortex. More frequently, the wave was delayed (to 6–9 min) was completely blocked in some areas of the cortex. Different types of mild convulsive activity could accompany both the rapid propagation of waves across the cortex and inhibition of wave development. In most cases, there were no electrophysiological signs of changes in neocortical excitability. However, alterations to the spatial characteristics of waves of spreading depression and the spontaneous appearance of repeated waves provided evidence of changes in the functional state of the brain. Overall, EEG spectral analysis in conscious rabbits allowed analysis of spreading depression both in cases of sequential propagation across the cortex and in cases of atypical modes of development of this phenomenon.

Dynamics of Changes in Electrical Activity in the Rabbit Cerebral Cortex during Sequential Sessions of “Animal Hypnosis”

The dynamics of changes in individual electrical activity rhythms in the premotor, sensorimotor, and temporal-parietal areas of the cortex in both hemispheres were studied in chronic experiments in rabbits during sequential sessions of “animal hypnosis.” These experiments showed that during the first session of “animal hypnosis,” significant changes in electrical activity occurred only in the premotor area of the cortex of the right hemisphere, where there were increases in spectral power in the delta-1 and delta-2 ranges and decreases in spectral power in other ranges of electrical activity. Subsequent sessions of “animal hypnosis” formed increasing changes in electrical activity, which were particularly marked in cortical areas in the right hemisphere. Significant changes in spectral power in the delta and theta ranges of electrical activity in cortical areas did not arise at the beginning of the hypnotic state, but after 4–6 min. During the third session of “animal hypnosis,” the course of electrical activity in the alpha and beta rhythms in the premotor and sensorimotor areas of the cortex became wave-like in nature.

Influence of music with different volumes and styles on recognition activity in humans.

The efficiency of the recognition of masked visual images (Arabic numerals) increased when accompanied by classical (62 dB) and rock music (25 dB). These changes were accompanied by increases in the coherence of potentials in the frontal areas seen on recognition without music. Changes in intercenter EEG relationships correlated with the formation a dominant at the behavioral level. When loud music (85 dB) and music of other styles was used, these changes in behavior and the EEG were not seen; however, the coherence of potentials in the temporal and motor cortex of the right hemisphere increased and the latent periods of motor reactions of the hands decreased. These results provide evidence that the “recognition” dominant is formed when there are particular ratios of the levels of excitation in the corresponding centers, which should be considered when there is a need to increase the efficiency of recognition activity in humans.

Suppression of EEG gamma activity--an informative measure of spreading depression waves in the neocortex of the conscious rabbit.

Spreading depression can arise spontaneously in convulsions, migraine attacks, vascular lesions, and other pathological brain states. However, the methodological complexity of recording a direct current potential in the neocortex in humans and conscious animals significantly limits studies of the functional consequences of spreading depression. The present report describes a detailed analysis of the EEG dynamics at the moment of development of spreading depression waves and identifies specific signs allowing spreading depression to be recorded without recording changes in the direct current potential. At the moment of arrival of spreading depression, the interhemisphere equilibrium is highly disturbed because of large decreases in high-frequency activity. The time parameters of the dynamics of the gamma-1 and gamma-2 ranges were the most informative features of the development of spreading depression waves. Increases in power in the delta range developed with some delay on the background of a deep inhibition of high-frequency activity and are in essence a consequence of spreading depression. The encephalographic criteria of spreading depression waves identified here can significantly simplify the detection of this phenomenon both in experimental and clinical conditions in a number of pathological brain states.

Recognition of visual images in a rich sensory environment: Musical accompaniment

Human recognition of visual images in the form of Arabic numerals affected by “noise” showed a reduction in the time needed for recognition and an increase in the probability of making a correct identification in a rich sensory environment (use of classical or rock music). There was no direct relationship between the volume of the music and its positive effect on the recognition of visual images. The greatest changes in the recognition time and quality of correct recognition occured at specific volume levels for both classical and rock music, and there were individual differences. The efficiency of image recognition decreased when the same musical fragments were used again with the same volume. The data are interpreted as a manifestation of the dominant.

Coherence analysis of the electrical activity of the rabbit brain in the presence of a hunger dominant.

A hunger dominant was created in rabbits deprived of food for 24 hours. The presence of summations was judged on the basis of the appearance in the response to sound of swallowing or chewing movements. When a hunger dominant is created, the coherence (Coh) of the electrical activity of the frontal, sensorimotor, and parietal areas of the cerebral cortex increases, especially in the range of the delta and theta frequencies. Variously directed coherence of the potentials of the lateral (LH), middle (VmH) hypothalamus and the cortex is established, the Coh of the potentials of the LH and cortex decreases, and of the VmH and the cortex, by contrast, increases. A definite mosaic of the coherence connections of the electrical processes of the hypothalamus appears: the Coh of the potentials of the LH and VmH increases, and the Coh between the potentials of the medial and lateral preoptic areas decreases.

Solution of Mathematical Logical Problems in a Sensory Enriched Environment (classical music)

Accompaniment of the solution of mathematical logical problems with classical music at levels of 35 and 65 dB led to decreases in problem solution times. Louder music (85 dB) had no significant influence on the problem solution process. Solution of mathematical logical problems without musical accompaniment led to increases in the coherence of potentials in the beta1, beta2, and gamma frequency bands in the occipital areas of the cortex, with a predominance in the left hemisphere. EEG coherence decreased in the frontal area of the cortex. Music decreasing problem solution time induced increases in left-sided EEG asymmetry. Accompaniment of problem solution by classical music increased both intrahemisphere and interhemisphere coherence of potentials in the frontal areas of the cortex. Use of louder music (85 dB) to accompany problem solution induced right-sided EEG asymmetry, and foci of coherence links also often appeared on the EEG of the temporal area of the right hemisphere.

The EEG during Solution of Mathematical Logical Tasks

A model creating a dominant focus in the CNS arising on solution of specially constructed mathematical logical tasks was developed. The dominant state was accompanied by increases in coherence in the delta range. The low-frequency ranges (dealt, theta, alpha) showed increases in combinations of potentials in the frontal cortex. In the high-frequency ranges (beta1, beta2, gamma), coherence decreased in the frontal areas of the cortex, while increases were seen in the central, parietal, temporal, and occipital areas, with a predominance in the left hemisphere. Significant changes in the numbers of connections (increases) were seen in diagonal coherence values. Analysis of EEG spectral power showed that solution of tasks was associated with generalized increases in values in the delta range across the cortex. Theta activity increased in the frontal cortex and gamma activity increased in the occipital areas. Spectral power in the alpha range mainly decreased.

Asymmetry of the Brain Electrical Processes in the “Animal Hypnosis” Phenomenon in Rabbits

The study of “animal hypnosis” in rabbits by means of thermoencephaloscopy showed that general cooling of the brain occurs, the right hemisphere cooling slower than the left hemisphere [5]. During “animal hypnosis,” the number of high correlation coefficients between the electrical activities in different regions of the right hemisphere increases; in the left hemisphere, the interrelationship between the electrical processes in the cortical zones decreases as compared with the control [5].

Coherence analysis of electrical activity in the rabbit brain during the process of substitution of dominants.

Coherence analysis was used to study intercenter relationships between biopotentials in the sensorimotor cortex (forelimb and blink representation areas) and the visual cortex in both hemispheres and the ventrolateral nucleus of the thalamus (VPL) of the left and right thalami during the formation of a motor defensive dominant (electrical stimulation of the limb skin) on a background of an induced (by stimulation of the cornea with an air jet) blink dominant. Characteristic electrophysiological measures of the dominant state (increases in the mean coherence level of potentials in the delta frequency range in, structures involved in the functional defensive limb reflex system), along with the absence of behavioral manifestations of the motor dominant in the blink dominant, indicated that a cryptic potential dominant focus was created in the CNS in these conditions, and that this affected ongoing animal activity.