The functional testing of the interhemispheric asymmetry in the spatial organization of rabbit cortical potentials]

Interhemispheric asymmetry was studied of spatial-temporal potentials organization (STPO) of the cortex in non-fixated animals in the states of deep rest, behavioural activity and in the transition period between them. Despite the intrahemispheric differences of the STPO in each of these states, interhemispheric divergences in the character of reconstructions of momentary topograms of the cortical potentials, recorded at 24-channels leading, are limited by 35% of the epoch analysis time. Comparison of the dynamics of intrahemispheric changes of topograms of cortical potentials in the left and right hemispheres in the states of rest and activity revealed a narrowing of temporal period of the absence of resemblance in reconstructions of successive topograms of the left and right hemispheres in comparison with transition processes. In the phase of rest the interhemispheric conjugation of spatial reconstructions in topograms became lowered mainly because of the disturbances of monotony of changes of their reliefs in one of the hemispheres in turn. In the active phase, deviations from STPO of the cortex, characteristic of the state of rest, were met more frequently in the right hemisphere; in that case oscillations of the topograms general mean level connected with the activity of non-specific activating subcortical brain system acquired a significant role in regulation of interhemispheric relations. Presence of interhemispheric resemblance of reconstructions of topograms reliefs in the active phase, despite the tendency to its lowering in comparison with the rest, testifies to the contribution also of the intracortical processes to the interhemispheric spatial synchronization of the cortical potentials in this state.     

Interhemispheric asymmetry of the spatial-temporal organization of human cortical potentials during the performance of an intellectual task

In 15 healthy subjects, during accomplishment of an intellectual task spatial-temporal organization of potentials (PSTO) of the left and right cerebral hemispheres was studied by the method of quantitative evaluation of successive topograms (momentary values of potentials under leading electrodes). It was found that the time of absence of resemblance (TAR) in the cortical PSTO during intellectual activity occupied totally 10-30% of the recording time what is considerably less than in the state of calm alertness where this time varied within 4-57%. Productivity of task accomplishment apparently is connected to a greater extent with TAR than with the character of intrahemispheric reconstructions of the PSTO.     

Analysis of interhemispheric asymmetries in the space-time organization of human cortical potentials

The study of spatial organization of human cortical potentials with multichannel recording (48 leads) has shown, that different functional conditions of brain (quiet alertness, excitation after caffeine administration, intellectual strain, negative emotional shifts, inhibition after administration of neuroleptics) are accompanied by synchronization changes in the left and right hemispheres specific of each brain condition. Similar shifts may be recorded both in states similar by their phenomenological characteristics (after administration of caffeine and during intellectual strain) and during the opposite levels of alertness (emotional strain and administration of neuroleptics).     

The topography of functional interhemispheric asymmetry in the visual cortex]

Functional interhemispheric asymmetry was investigated by evoked potentials method in experiments on ten cats under ethaminal anaesthesia at 200 points of the visual cortex during the action of binocular and monocular photic flashes of submaximal intensity. Topographic maps have been plotted of the functional interhemispheric asymmetry. In most of the animals a hemisphere dominant and non-dominant at the given moment can be singled out. Section of the callosal body leads to reduction of the functional interhemispheric asymmetry due to a decrease of the focus of maximum activity in the dominant hemisphere and its increase in the non-dominant one. A mozaic pattern of functional interhemispheric asymmetry has been demonstrated, as expressed in the existence of zones of inverse dominance along with prevailing zones of direct dominance. Section of the callosal body produced a decrease in the area of direct dominance and an increase in that of inverse dominance. Absolute interhemispheric asymmetry was most pronounced in the central part of the visual cortex (field 18 and its medial boundary) and the relative one, on the periphery of the visual area (fields 17 and 19).     

The interhemispheric brain asymmetry of the rabbit in a state of "animal hypnosis"]

By the method of forced immobilization the rabbits were brought into the state of "animal hypnosis" (immobilization reflex), and their ECoG was recorded, which was further processed on the computer. It was found that during hypnosis a functional interhemispheric brain asymmetry was developed in rabbits with activity predominance in the right hemisphere. The "animal hypnosis" is a phasic process: in the ECoG of the rabbit under hypnosis a regular alternation of delta and theta activity takes place. Electrophysiological reconstructions in the rabbit brain during the change of its functional state correlate with the brain thermal reactions, revealed earlier.     

The spatial organization of the cortical potentials in exposure to different forms of photic stimuli]

Reactive changes of spatial-temporal organization of cerebral cortex potentials of rabbits under the action of light stimuli of various shapes (circle, square, triangle, cross and weaker diffusive light presented prior to and after the application of structural stimuli) were studied on the basis of multi-channel EEG recording data (24 leads). The data were evaluated of spectral-correlative analysis of the electrical activity and the results of comparison of successive momentary topograms of cortical potentials (EEG) on two-second segments prior to and during the action of the applied light stimulus. The obtained results showed that localization of interconnected changes of the cortical potentials were more sensitive to the perception of the form of light stimuli than the change of frequency characteristics of the EEG rhythms.     

The effect of sex steroid hormones on interhemispheric asymmetry in rats]

The effect of gonadectomy and sex-steroid hormones treatment on functional interhemispheric asymmetry to the reaction of pain cry avoidance of another species (emotional reactions) and motor and exploratory activity of open-field behavior in Wistar rats of 3 months old has been investigated. A spreading depression technique for hemisphere inactivation has been used. The hemispheric asymmetry of the reactions in intact rats was characterized by sex dimorphism; the left hemisphere dominated to a great extent in males than in females under the control of emotional reactions; in motor and exploratory activity in open-field behavior of rats the left hemisphere dominated in males and the right one--in female. In both sexes the neonatal gonadectomy levelled the interhemispheric differences in reactions under investigation. The following treatment of females with estradiol and males with testosterone didn't restore the asymmetry. After the castration at the age of 3 months the correlation between the size and direction of interhemispheric differences became reverse. The treatment of females with testosterone and males with estradiol both castrated in adulthood restored the interhemispheric asymmetry in males and had no effect in females. The treatment of intact rats with hormones of opposite sex led to the enhancement of left hemisphere dominance in motor and exploratory activity in males and levelled the asymmetry in females. It has been shown that in adult rats sex-steroids effect predominantly the right hemisphere.     

Interhemispheric asymmetry of the spatial organization of human cortical potentials during the perception of emotional and indifferent images

In 13 healthy subjects dynamic characteristics of potentials spatial-temporal organization (PSTO) in the cortical left and right hemispheres at presentation of emotionally coloured and indifferent graphic images were studied by the method of quantitative evaluation of subsequent electroencephalotopograms. It is shown that, in contrast to the state of calm alertness, presentation of emotional and indifferent images leads to a decrease of the time of discordance in the hemispheres activity i.e. to synchronization increase. At the action of emotionally coloured images differences were found between the reorganizations of the left and right hemispheres, while there were no such differences at the presentation of indifferent images.     

Thermal interhemispheric asymmetry of the brain in rats in a cataleptic state]

The rat brain thermal fields were studied using the thermoencephaloscopic technique in three experimental conditions: the genetic catalepsy (GC rat strain), cataleptic phase of an audiogenic epileptic seizure (Krushinski?-Molodkina strain), and pharmacological catalepsy produced by haloperidol injection (Wistar rats). Irrespective of the experimental conditions, the state of catalepsy, accompanied by a decrease in the muscle tone and inhibition of motor reactions, was characterized by total asymmetric cooling of the brain cortex with the dominance of the right hemisphere. Temperature difference between the parieto-occipital areas of the right and left hemispheres reached 0.3-0.6 degree C.     

Effect of masking on interhemispheric and bilateral asymmetry of long-latency auditory evoked potentials

Considering the effects of noise on the amplitude of long-latent auditory evoked potentials, it is concluded that masking interference diminishes the right hemisphere dominance in the processing of the non-speech acoustic information. The decrease is observed both with the monotic and dichotic delivery of signals and noise. With monotic presentation masking interference also decreases the extent of the lateralization of monaurally delivered information predominantly to the contralateral hemisphere.     

The effect of scopolamine on the spatial organization of rat cortical potentials

The influence of scopolamine (1 mg/kg, i.p.) on the spatial organization of the neocortical electrical activity was studied in rats. A decrease in the spectral power and coherence of brain potentials in the range of the dominant theta-rhythm peak (6.00-7.25 Hz) and their increase in the adjacent low-frequency band were observed. Both indices were decreased in the wide beta band (19.00-30.00 Hz). The described changes took place over the whole areas of the right hemisphere and parieto-temporal region of the left hemisphere. The obtained results are discussed with respect to the role of the cholinergic brain system in the higher nervous activity.     

The study of interhemispheric asymmetry in spatial-perceptive problem solving

Features of brain interhemispheric asymmetry during solving the spatial figurative task (maze model) were studied in men and women with different intelligence quotients (IQ). It was shown that during task solving the rate of information processing was higher in the right brain hemisphere, and amplitude characteristics of the event-related potentials were higher in the left hemisphere. No gender and IQ differences in the character of interhemispheric interaction were found during the realization of the maze-model task. The results testify that the character of hemispheric interaction depends om the task rype rather than gender and intelligence level.     

The effect of gonadectomy on interhemispheric asymmetry in rats

The influence was studied of the gonadectomy in the newborn and mature male and female rats on functional interhemispheric asymmetry of the reaction of avoidance of pain scream of another rat ("emotional resonance"), and motor and investigatory activity in the open field. Consecutive inactivation of the hemispheres was realized by K+ spreading depression. It has been shown that neonatally gonadectomized rats have no interhemispheric asymmetry of the studied reactions. In male rats gonadectomized in mature state, interhemispheric asymmetry of "the emotional resonance" reaction is not significant and in the motor and investigatory activity in the open field, in contrast to intact animals, the right hemisphere is dominant and not the left one. Ovariectomy of mature female rats led to the increase of the dominance of the left hemisphere in the control of "the emotional resonance" and change of the right hemispheric dominance in the control of the motor and investigatory activity in the open field for the left hemispheric one. Gonadectomy of male and female mature rats had an opposite effect on the functioning of the right hemisphere: facilitating in male rats and inhibitory in female ones.     

Electrophysiologic characteristics of functional interhemispheric asymmetry

Change of biopotentials spatial synchronization under functional loads addressed predominantly to one or the other hemisphere (correlative analysis of the first EEG derivative of more than two thousands healthy subjects of various age), allowed to single out three phenotypes of hemispheric relations differing mainly by different types of information processing: right-hemispheric, left-hemispheric or mixed. Expressed EEG activation in both hemispheres (judged by alpha-index change) is manifest when the subject is presented with a task, the context of which does not correspond to the initially dominating type: in right-hemispheric--at solution of tasks, oriented to logical-verbal context and in left-hemispheric--to spatial-image one. The high level of non-specific EEG activation may be considered as an attempt of compensation of relative functional insufficiency of the right hemisphere systems in initially left-hemispheric or left-hemisphere systems in right-hemispheric individuals.