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Biomedical subjects

V V Lavrov

Publications and source records attributed to V V Lavrov.

At least 19 recordsLinked to original sources
PubMed1992

[The activation and inhibitory postactivation effects of chemical interoceptive stimulation under normal conditions and in experimental neurosis].

The realisation of hemointeroceptive effects was found to begin with a period of the brain activation. In normal conditions a positive correlation was found between the EEG arousal response and the concentration of mustard administered into the stomach. In experimental neurosis, both regulatory influences of the hemointeroceptive stimulation were decreased.

Animals↗
PubMed1991

[An increase in the excitability of nonspecific cortical formations during a decrease in the level of influences from the brain stem reticular formation].

In chronic experiments on alert unrestrained cats with cortical implanted electrodes, the thresholds of EEG activation to electrical stimulation were investigated in normal cats and in animals with diminished influences from the mesencephalic RF. Comparative analysis of the thresholds revealed an increase of the cortical unspecific excitability in diminished reticular influences. The relation of this increase to the neurophysiological mechanisms of neurotic pathology is discussed.

Animals↗
PubMed1989

[The dynamics of superslow oscillations in multineuronal activity and bioelectrical potentials of the cat brain during unreinforced photic stimulation].

The slow changes of the electrocorticogram, the multineuronal activity, the cortical EEG and the cat behaviour were simultaneously observed in chronic experiments before and after light stimulation of different intensity. The slow electrical potentials correlated with changes in the multineuronal activity, the correlation increasing with the amount of recorded neurons. A different character of the slow changes in electrogram (synchronization and desynchronization) and multineuronal activity (excitation and inhibition) in response to the light stimuli, was revealed. The slow electrophysiological processes seem to depend on the light intensity to a lesser extent than the EEG reactions.

Animals↗
PubMed1988

[Role of specific and nonspecific afferent currents in forming evoked brain potentials to photic stimulation in the cat].

Evoked potentials during light stimulation were investigated in normal cats and after bilateral destruction of specific (the optical tracts, the lateral geniculate nuclei) and nonspecific (the brachia colliculi superioris) visual pathways. A component corresponding to the primary response was present in evoked potentials in all cases. It is concluded that photoinduced responses mainly depend on the quantity but not on the quality of the exciting afferent flow.

Afferent Pathways↗
PubMed1986

[Source of light-evoked cortical activity after destruction of the main visual pathway].

Electrical responses to flashes and single electrical stimuli applied to optical nerve were recorded from the visual and sensomotor cortex, the lateral geniculate nucleus, the hypothalamus and the caudate nucleus in normal cats and after bilateral lesion of the specific visual pathways. The light-imduced EPs were preserved after transection of the optical tracts and after lesion of the lateral geniculate nuclei. The EPs to flashes were absent after transection of the optical nerves. After lesion of the lateral geniculate nuclei, sparing all optical tract connections to the colliculi superior, activation of the EEG was possible with strong light flashes. The significance of the retino-hypothalamic and retino-collicular connection for formation of the light-induced cortical responses, is discussed.

Animals↗
PubMed1982

[Participation of the lateral geniculate body in the mechanisms of brain activation].

In chronic experiments on cats with intact LGB, electrical stimulation of the latter (120-190 microA) caused brain activation with the same threshold as the stimulation of the mesencephalic RF or of the thalamic CM with 50-80 microA. With all but the geniculo-cortical connections of the LGB disrupted, the threshold for brain activation increased to 220-400 microA. After LGB coagulation leaving intact all optical tract connections to the superior colliculi and to the brain stem, the adequate cortical activation was only possible with very strong light flashes (250-1000 l). This suggests that the LGB participates in unspecific brain mechanisms and can induce cortical activation regulated afterwards by the cortex itself.

Animals↗
PubMed1981

[Activation response to photic stimulation in normal cats and after transection of the afferent pathways of the mesencephalic reticular formation].

In chronic experiments on waking unrestrained cats with implanted electrodes the reaction of EEG activation to light stimulation was recorded in two sets of experiments in normal cats and in animals with transsection of brachia colliculi superioris that separated mesencephalic reticular system. The intensity of the activating reaction in the intact cats increased ith a rise in the light stimulus intensity. In the cats with brachia-colliculi superioris transsected there was no definite dependence on the stimuli intensity and the intensity of the activating reaction changed randomly. It is suggested that this irregularity is accounted for by blocking of the excitating afferent flow usually coming to the mesencephalic reticular formation through brachia and colliculi both from the visual pathways (ascending flow) and from the cortex (descending activation regulating flow).

Animals↗
PubMedDate not supplied

Cyclical processes in neuronal populations of the cat somatosensory cortex during extero- and interoceptive activation and in the course of its extinction.

The EEG reactions were recorded in chronic experiments in awake cats and the slow periodic changes in the frequency of the multicellular impulse activity were observed at points (standard localization) of the somatosensory (1) zone of the cortex. Results of the analysis of both processes were combined in graphs in a single time scale. The correlation of the expressivity of the activation reaction and degree of modulation of the cyclical fluctuations of the frequency of the impulse activity were followed both during the action of exteroceptive (conditional, light; unconditional, sound) and the interoceptive (mechanical and chemical) stimuli. A particular characteristic of the interoceptive stimulation as compared with the exteroceptive consisted in the inertia of the respondent reaction and the lesser contrast in relation to the background. During the extinction of the responses the decrease in the activation reaction correlated with a decrease in the initial (after the switching on of the stimulus) fluctuation of the frequency of the multicellular impulse activity. The data obtained serves as proof of the unity of the two processes: the regulation of the activation of the brain and the regulation of the periodicity of the neuronal impulse activity.

Acoustic Stimulation↗
PubMedDate not supplied

Increase in excitability of cortical nonspecific structures in the presence of a decreased level of influences from the brainstem reticular formation.

The results of the measurement of the threshold of electrical stimulation of the cortex sufficient to elicit the EEG activation reaction in the norm and under conditions of the reduction of influences from the brainstem of the reticular formation are presented. A decrease in the thresholds was observed in those conditions which are regarded as evidence of an increase in the excitability of the nonspecific cortical formations. The increase was uneven: it was maximal in the sensorimotor and minimal in the visual cortex. It is hypothesized that the data obtained in brain preparations with a decreased level of brainstem reticular influences may be applied to the understanding of certain phenomena of neurotic pathology in its neurophysiological aspect.

Animals↗
PubMedDate not supplied

Participation of the lateral geniculate body in mechanisms of brain activation.

The significance of the lateral geniculate body for nonspecific activation of the brain was elucidated in experiments on cats. It was established that when the connections of the lateral geniculate body remain intact, its stimulation elicits the usual activation of the EEG, but at higher threshold values of the current (120-190 microA) than when the mesencephalic reticular formation of the medial center of the thalamus is stimulated (50-80 microA). If only direct connections with the cortex remain, however, and the others are disrupted, the threshold for activation increases to 220-400 microA. When the lateral geniculate body is coagulated, cortical activity occurs only in response to very bright light flashes (250-1000 1x). All of this indicates that, in addition to carrying out its principal function of processing and sending the basic flow of visual impulsation to higher optical centers, the lateral geniculate body may be the source of activating transmissions sent to the cortex. Nonspecific stimulation that develops in the cortex is subsequently regulated by the cortex itself; the cortex plays a leading role in these processes.

Animals↗
PubMedDate not supplied

[Electrical reactions in the cat brain during differentiation of photic stimuli].

Study of EEG responses to photic conditioned stimuli in cats has shown that the extent of brain activation depends not on the physical strength of the stimulus, but on its biological significance. The longest activation is recorded to a positive signal, even if it is the weakest flash of light. The intensity of EEG responses to negative stimuli is determined by the nearness of their physical parameters to those of the positive signal. Repeated presentation of a non-reinforced flash leads to a gradual extinction of EEG reactions. Brain activation in response to a reinforced positive signal persists unchanged even after a large number of its repetitions. The revealed properties of brain electrical reactions to stimuli of different significance accord with those previously recorded in response to acoustic stimuli. In both cases the data are in agreement with hypothesis of a central system of signal analysis, which performs the estimation of stimuli according to their biological quality.

Animals↗
PubMedDate not supplied

[The regulatory effect of the functional status of the cat on the perception of an external afferent stimulus].

Experiments were conducted on cats by conditioned food-procuring method. Behavioural, vegetative reactions and a set of electrophysiological characteristics were recorded. It was found that regulatory influence of an extraneous stimulus and of artificial excitation of the brain was expressed in an increase of reactivity to conditioned and unconditioned sensory stimuli and in disinhibition of effector responses. This influence was realized not only during the development of EEG activation reaction but could be preserved over a long period in conditions of the deactivated brain state. Regulatory influence of interceptive factors is characterized by a decrease of reactivity and by inhibition of effector responses. As in the case of external effects, the realization of this influence begins with a period of brain activation and is preserved for a long time in conditions of deactivated state.

Afferent Pathways↗
PubMedDate not supplied

[Effect of pretuning of the visual analyzer and activation of the brain on the development of experimental neuroses].

It is shown that pretuning of analyzer system is a factor initiating a sharpening of the analysis and subsequent development of experimental neurosis resulting from excessively acute differentiation. A number of behavioural and electrophysiological characteristics was recorded in cats in norm and in neurotization. Pathological action was established of both artificially increased and lowered brain activation. The increase was reached by additional electrical stimulation of various cortical and subcortical brain structures. The lowering took place following isolation of the reticular formation from the visual system. In response to artificial increase of excitation in neuroticized animals seizures took place. The obtained facts confirm the suggestion that pathogenesis of neurosis is accompanied by disturbance of normal activity of activation-deactivation mechanism.

Animals↗
PubMedDate not supplied

[Significance of presetting an analyzer system in discriminating light intensity in the cat].

EEG and behavioural reactions were studied at the action of signal and nonsignal light flashes. The minimal time of stimulus exposition necessary for preserving differences in EEG activation reactions to nonreinforced stimuli of different intensity (in a diapason from 3.5 to 250 lk) was shown to exceed 1 s. After giving the signal meaning to the flashes the minimal time of stimulus exposition when the animals were capable to discriminate intensity of the flashes (in a diapason from 3.5 to 30 lk) just at the first presentation, was equal to 0.1 s. Decrease of the minimal time of stimulus exposition necessary for discrimination of the light signals was supposed to be stipulated by their biological significance and presetting of the analyzing system being organized by preliminary learning a crude analysis of stimuli. Discrimination of the light stimuli of short duration was impossible without such presetting.

Animals↗
PubMedDate not supplied

[Analysis of photic signals by cats according to their intensity following transection of the superior quadrigeminal brachii].

In experiments on cats trained by the motor alimentary conditioned method to discriminate photic stimuli by intensity, EEG changes were studied when differentiating signals of different biological significance before and after transection of the brachii of the superior colliculi. The normal direct proportional dependence of pronouncedness of brain electrical reactions on the complexity of stimuli analysis was disturbed after transection. The operated animals retained only the capacity for a rough differentiation by brightness, the fine gradation of EEG responses to negative signals of different fineness being lost. The disturbance of interaction between the analysing and activating brain systems after transection of the brachii may be due to both the lack of non-specific ascending tonic influences of the midbrain reticular formation on the cortex, and to the destruction of many pathways for corticofugal control of the activity of the brainstem non-specific apparatus.

Animals↗