Correlation of the neuronal impulse activity of different areas of the neocortex in rabbits in the switching of positive and inhibitory conditioned reflexes

By cross-correlation method conjugation in impulse activity of pairs of simultaneously recorded units in the visual and sensorimotor areas of the neocortex (representations of the conditioned and unconditioned stimuli) was studied during the switching of defensive positive and inhibitory reflexes in rabbits. 30-second fragments of impulse activity were analyzed in intervals before and after three presentations of positive and inhibitory conditioned stimuli (CS). The activity of single pairs of units in the process of stimuli presentation was characterized by instability. Only in 29% of 51 units' pairs the presence or absence of correlation between their discharges was stable. Analysis of activity of 75 pairs of units showed differences in impulse activity in inhibitory and positive tonic reflexes. The number of pairs of correlated units in about 30 s after inhibitory CS decreased (27%) in comparison with the interval before its action (52%). In the inhibitory tonic conditioned reflex, temporal intervals of discharges of one unit correlated with discharges of the second unit undergo changes. The obtained results testify that such parameter as the number of pairs of units with correlated activity in intersignal time interval is very important for the realization of motor reaction to conditioned stimuli.     

Effect of sodium nitrite on the activity of the neocortex neurons during realization of defense and inhibition conditioned reflexes

A decrease in intensity and duration of short-latency reaction components of the sensorimotor and visual cortical neurons to specific stimuli (pain reinforcement and light flashes, respectively) was observed after the administration of NO-generating sodium nitrite (11 mg/kg, subcutaneously). Activation decrease in the visual cortex took place irrespective of biological significance of the light flashes, i.e., in case when this stimulus was a signal of defensive conditioning and in case when these flashes were applied with continuous light (a conditioned inhibitor). Sodium nitrite almost did not change the late activation of sensorimotor and visual neurons in response to pain reinforcement and disinhibitory action of the latter. The results confirm the viewpoint about different neurotransmitters in "specifically modal" and "non-specific" pathways to the neocortex during learning.     

Effect of piracetam on the neuronal activity of the neocortex and on behavior in rabbits during learning

Against the background of the action of piracetam--a cyclic derivative of GABA--in a dose of 200-400 mg/kg, no significant changes were observed of probabilities of motor reactions to inhibitory and reinforced light flashes. Piracetam in that dose did not affect inhibitory pauses in responses of neurones in the visual area and corresponding late components of the evoked potential to nonreinforced light flashes, i.e. it did not intensify inhibitory hyperpolarization processes in the cerebral cortex. Piracetam administration improved differentiation of inhibitory and reinforced light flashes judging by bioelectric parameters of the brain activity as a result of intensification of pain reinforcement action on cortical neurones. The carried-out experiments revealed significant differences in neurophysiological mechanisms of action of piracetam and fenibut--GABA linear derivate related to nootropic class.     

Interhemispheric asymmetry of neocortex and hippocampus in orienting exploratory behavior of rabbits

Correlation of discharges of cortical neurons in symmetrical points of the visual and parietal cortices and left and right hippocampal CA1 neurons was studied in freely moving rabbits during exposure to emotional stimuli. Crosscorrelation histograms were plotted. As compared to the initial state, during an active orienting exploratory reaction to stimuli, the left-side influence on right-hemispheric cortical neurons with a delay about 100 ms increased, which led to asymmetry in interhemispheric interaction with the left-side dominance. During freezing, the left-side influence became weaker, and the effects of the right hemisphere prevailed. Hippocampal asymmetry in neuronal activity was in reciprocal relationship with neocortical asymmetry. In the hippocampus, the right-side influence with a delay about 200 ms increased during the active exploratory reactions resulting in the right-side dominance. Freezing was accompanied by strengthening of the left-side influence (the left-side dominance). During the active locomotion, neuronal interaction in the hippocampus was predominantly realized in the theta-range frequency, whereas freezing was characterized by the delta-range correlation. It was concluded that the active or passive nature of a behavioral reaction to emotional stimuli was correlated with changes in asymmetry in the interhemispheric neuronal interactions at the cortical and hippocampal levels.     

Effect of electrical stimulation of the hippocampus and neocortex on cingulate cortical neurons in rabbits

Extracellular unit activity of the anterior and posterior zones of the cingulate cortex and also of the anterior and posterior cortical association areas was analyzed in unanesthetized rabbits. In the posterior zone considerably more cells (60%) responded to hippocampal stimulation than in the anterior zone (18%). In 43% of these cells in the posterior zone but only in 5% in the anterior zone, the responses followed the frequency of stimulation. Unit responses in the posterior zone could be divided into two discrete groups: those with short (12.3 ± 6.5 msec) and those with long (50.2 ± 10.0 msec) latent periods. Inhibitory phenomena also were well marked during hippocampal stimulation. More than one-third of cells of the cingulate cortex responded to stimulation of the posterior association zones by spikes which followed the stimulus, and by subsequent inhibition. Responses of this kind to stimulation of the anterior association zones were found in only a few cells in the anterior zone of the cingulate cortex. The results are discussed in the light of data from morphological investigations relating to connections between these structures.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 270–277, May–June, 1982.     

Kallikrein effect on the acquisition and extinction of conditioned reflexes in rats

The effect of kallikrein was studied on the acquisition and extinction of conditioned reactions in rats. It was demonstrated that kallikrein in doses of 50 and 100 mu/kg i.p. accelerated the process of learning in these animals. The observed effect might be connected with a rise in the activity of kininogenic enzymes in the central nervous system.     

Analysis of changes in the electrical activity of the neocortex in dogs during the formation of the stereotype of food-procuring conditioned reflexes in them

A system of food-procuring conditioned reflexes (dynamic stereotype after I.P. Pavlov) was elaborated in dogs. In the interstimuli periods, 0.6 to 0.8 sec. prior the action of the conditioned stimulus, they exhibited a "state of expectancy" characterized by an increase of frequency (up to 80 per sec.) of potential oscillations of a small amplitude (20 to 30 mcv) and their pronounced sychroneity, predominantly in the anterior parts of the neocortex. The conditioned signal acting against such background produced specific reactions in the form of a limited number of bursts (3 to 4 in 0.5 sec.) of highfrequency (up to 100 per sec.) synchronized activity (HSA) of considerable amplitude (50 to 60 mcv) which always preceded conditioned reactions, being in certain temporal relations with them. A correlation-spectral analysis has shown that in the HSA period, electrical activity became considerably more regular; in the intensity spectra the extreme frequencies of the analyzed band (5 to 7 c/s and 90 to 100 c/s) became prominent, and in most cases high values of the coherence function were due to them. HSA reactions are regarded as a major link in the trigger mechanism of conditioned food-procuring reactions.     

Correlation of neuronal reactions of different regions of the neocortex of the rabbit to conditioned positive and inhibitory stimuli

The activity of neurones of the visual and sensorimotor areas of the neocortex was simultaneously recorded in rabbits under the action of conditioned, inhibitory stimuli (CS, IS) and at simultaneous presentation of CS and the unconditioned stimulus (US) after trans-switching of the positive and inhibitory conditioned reflexes. Mean time of conjugated reactions of simultaneously recorded pairs of neurons is similar under the action of CS, combined action of CS and US and under IS. During the IS action as compared with CS, the phasic activity of some neurones in different areas increased, and due to this the similarity of reactions also increased; in other pairs of neurones the reactions weakened and the responses similarity decreased. The frequency of the appearance of intervals of the conjugated excitation after CS corresponds to 4.3 Hz; under combined action of CS and US it increases up to 5.9 Hz, and after IS--it decreases to 3.6 Hz. The order of coming into conjugated action of different pairs of neurones changes depending on the signal significance of the stimuli.