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V N Andreeva

Publications and source records attributed to V N Andreeva.

10 recordsLinked to original sources
PubMed1977

[Low-threshold mechanisms and pathways of corticofugal activation].

In chronic experiments of alert cats, moderate electrical stimulation of different points on the lateral cortical surface led to activation of different cerebral areas. Both the high-threshold and the low-threshold points were revealed in the sensorimotor cortex and in the Ep field of auditory area. The latter had as low a threshold of the activation response as the points within the mesencephalic RF and the thalamic CM, VPL and GM. In the morphological aspect, projections from the auditory Ep field to the thalamic intralaminar nuclei and to the brain stem RF, were revealed. Major projections spread from the dorsal part of the Ep field to the lateral tegmentum. The data obtained seem to provide better comprehending of the mechanisms for corticofugal activation. The functional role of the low-threshold loci in the cortex can involve triggering of unspecific apparatus of activation with a graduated volley which controls its excitation in accordance with biological significance of analysed signals.

Animals↗
PubMed1975

[Extinction of brain activation responses to direct electrical stimulation of its structures in normal awake cats].

In unrestrained cats, repeated electric stimulation of the mesencephalic reticular formation (MRF), center median (CM) of the thalamus, and different cortical areas: both the low--and the high--threshold points (in regard to the brain activation), with the threshold strength current evoked similar EEG reactions of activation which diminished and disappeared after 3--5 repetitions of the stimuli. The moderate strength current evoked, apart from the EEG activation, pseudoviolent movements (turning of the head, etc.) and changes in the breathing rate. All these reactions could be extinguidhed by sufficient number of repetitions of stimuli, the effector reactions disappearing first, the EEG changes--last. The essential difference of the stimulation effects emerged when the strong current stimulation was used. In this case, when stimulating the high-threshold cortical points, the EEG and effector reactions could be abolished during long enough repetition of the stimuli, but it was impossible when stimulating the low-threshold cortical points, the MRF or CM: all the reactions stayed intense and stable, the animals became highly irritated. The data obtained are discussed from the point of view of the authors' concept of the interaction between the activating and integrative analysing mechanisms of the brain.

Animals↗
PubMed1975

[Arousal thresholds during stimulation of brain structures in nonanesthetized cats].

In cats, there was no apparent difference between the average low thresholds for evoking EEG arousal when stimulating the mesencephalic RF, thalamic CM or some cortical structures (sensorimotor area, inferior part of auditory Ep). Most of other cortical points had much higher thresholds (g. lateralis anterior, g. suprasylvius posterior, g. ectosylvius med. and sup.). The possible role of some cortical and mesencephalic structures in the brain activating mechanisms is discussed.

Animals↗
PubMedDate not supplied

Low-threshold mechanisms and cortical activation pathways.

In chronic experiments with alert cats, stimulation with electrical current of moderate strength at various points on the lateral surface of the cerebral hemispheres leads to activation of various brain regions. In addition to high-threshold cortical points, low-threshold points have been discovered which are located in the sensorimotor region and in the Ep field of the auditory zone. The latter possess the same low thresholds for evoking an activation response as do points in the mesencephalic RF and the thalamic CM, VPL, and GM. Connections have been discovered (in the morphological part of the study) between the auditory Ep field and the intralaminar nuclei of the thalamus and the brain-stem part of the RF; the major projections run from the dorsal part of the Ep field into the lateral zone of the tegmentum. It is proposed that the role of the cortical low-threshold foci could involve the triggering of the nonspecific activation apparatus in accord with the biological significance of the signals being analyzed.

Animals↗
PubMedDate not supplied

[The disinhibitory influence of the activating system when artificially excited from different points in the brain].

EEG activation can be produced by electrical stimulation of some cortical points with the same threshold current strength as by the midbrain RF and thalamic CM stimulation. Near-threshold stimulation of all these points acting simultaneously with inhibitory conditioned signals does not disturb the effector inhibition but displays an EEG difference between negative signals: the fine differentiation sound evokes considerable EEG desynchronization, while the rough one does not change the background rhythms. The same stimulation combined with a positive signal which has been made ineffective by successive inhibition or extinction, reestablishes the intensive EEG activation in response to this signal and the effector conditioned reflex. Therefore a mode-rate additional stimulation of the activating points in the cortex, RF and CM has a disinhibitory influence. When initiated in the cortex this influence may be transmitted from the cortical point to other parts of the brain along transcortical and corticofugal connections.

Animals↗
PubMedDate not supplied

[Generalization of activation reaction extinction during consecutive stimulation of different parts of the brain].

The process of extinction of the brain activation reactions ("arousal") was studied in chronic experiments on cats with implanted electrodes during repeated electrical stimulation of alternated points in the cortex and in the brain stem reticular formation. Extinction of the reactions achieved by stimulation of one point resulted in the loss of excitability both at this point and in other activating structures at different levels of the brain. The sequence of stimulated structures was of no importance. A possibility is suggested of development of a generalized inhibition in the neural net of the non-specific reticular system of the brain which may be inciated in any point of this system: in the brain stem, in the thalamus or in the cortex.

Animals↗