A. V. Bogdanov

Effects of “animal hypnosis” on a rhythmic defensive dominant

A defensive dominant was created in rabbits using rhythmic electrocutaneous stimulation of the left forelimb at a frequency of 0.5 Hz. After stimulation ended, the latent excitation state was tested using sound stimuli. Animals responded either with increases in non-rhythmic paw muscle activity or with rhythmic twitching of the paw at a frequency close to that of the electrocutaneous stimulation. After hypnotization, the incidence of rhythmic responses to the stimulation testing the dominant focus increased, while the incidence of non-rhythmic responses decreased.

The assessment of the strength of interaction between neurons of the motor cortex of the cat in a conditioned reflex to time

The study was carried out in cats, with the recording of multineuronal activity of the motor cortex during the development of a conditioned reflex to time. The strength of the interaction between adjacent and remote neurons within a range of 0.5 mm was assessed. The dynamics of the strength of the interneuronal interaction did not correlate in the overwhelming majority of cases with the dynamics of the frequency of the impulse activity of the neurons under investigation. Changes in the strength of interaction between neurons separated from one another in a conditioned reflex (CR) to time were encountered more often than between adjacent neurons; this may serve as additional evidence in favor of the hypothesis of the more rigid structure of connections within microsystems and the greater plasticity of connections between microsystems.

Correlations between Neuron Activity in the Sensorimotor Cortex of the Right and Left Hemispheres in Rabbits during a Defensive Dominant and “Animal Hypnosis”

A latent focus of excitation with a rhythmic nature (a defensive dominant focus) was created in the CNS of rabbits. The focus was formed by threshold electrocutaneous stimulation of the left forelimb using series of impulses consisting of 15–20 stimuli with interstimulus intervals of 2 sec. The linked activity of cells in the sensorimotor cortex of the right and left hemispheres was analyzed. When cross-correlation histograms of the spike activity of sensorimotor cortex neurons in the left hemisphere were constructed and analyzed in relation to spikes of high and intermediate amplitude recorded in the right hemisphere, the linked activity of 15% and 23% of neuron pairs, respectively, showed predominance of a rhythm equal or close to the stimulation rhythm used to form the dominant focus. When the appearance times of spikes from neurons in the sensorimotor cortex of the right hemisphere were analyzed in relation to spikes of high and intermediate amplitude recorded in the cortex of the left hemisphere, predominance of 2-sec rhythms was seen in the linked activity of only 3% and 10% of neuron pairs, respectively. After induction of “animal hypnosis,” differences between the hemispheres in relation to this measure leveled out.

Linked Activity of Neurons in the Sensorimotor Cortex of the Rabbit in the State of a Defensive Dominant and “Animal Hypnosis”

A cryptic focus of excitation (a dominant focus) was created in the brains of rabbits by threshold stimulation of the left limb with a current at a frequency of 0.5 Hz. After creation of a focus, there were equal probabilities of detecting pairs of neurons whose linked activity was dominated by a 2-sec rhythm in the sensorimotor cortex of both the right and left hemispheres (29.3% and 32.4%, respectively). When animals were placed in “animal hypnosis,” the total proportion of neuron pairs whose activity was dominated by the rhythm created by establishment of the dominant decreased significantly only in the right hemisphere (21%). After exiting the state of animal hypnosis, the proportion of neurons in the cortex of the right hemisphere whose activity was dominated by the 2-sec rhythm increased significantly if the neurons in the pair were close-lying but decreased significantly if the neurons in the pair were mutually distant. No such changes after hypnotization were seen in the cortex of the left hemisphere. In both the right and left hemispheres, dominance of the 2-sec rhythm in the activity of pairs of neurons was seen significantly more frequently when cross-correlation histograms were constructed by analyzing cells in relation to the spike activity of neurons generating spikes of the lowest (right hemisphere) or lowest and intermediate (left hemisphere) amplitude on neurograms of multineuron activity.

Correlated activity of sensorimotor cortex neurons in the left and right hemispheres of the rabbit brain in immobilization catatonia

Spike sequences extracted from multineuron activity from neurons in the sensorimotor cortex, and recorded simultaneously in the left and right hemispheres of the brains of rabbits in the state of immobilization catatonia (“animal hypnosis”) and on recovery of animals from this state were analyzed. Cross-correlation analysis of spike flows revealed a temporal relationship between the appearance of neuron spikes in the left and right hemispheres; these were regarded as the mutual influences of these neurons on each other. The intensity of the influences of left hemisphere neurons on cells in the right brain was shown to change significantly in relation to baseline measures at all stages of the experiment and at all of the time points studied. The intensity of the influences of neurons in the right hemisphere on cells in the left hemisphere changed significantly only after animals recovered from the state of immobilization and over much more restricted time periods.

Analysis of the Linked Spike Activity of Pairs of Neurons in Cortical Microstructures

Three behavioral models were used to analyze the dynamics of linked spike activity of pairs of simultaneously recorded cortical neurons. These experiments showed that the time distribution of linked cell activity can encode the parameters of the stimuli used.

Dynamics of the Assimilation of Rhythms of Electrocutaneous Stimulation by Sensorimotor Cortex Neurons in the Rabbit Brain

A dominant focus is a zone with stably increased neuron excitability in the cerebral cortex arising as a result of prolonged stimulation of some kind of effector (in our case the animal’s forepaw) or the direct cortical representation of this effector. Apart from increased excitability and stable excitation of the neurons within the zone, the dominant focus has two further very important properties – the ability of its neurons to sum excitation arriving in the cortex and propagating across cortical neural networks and inertia. This latter property is manifest as activation of the reaction in response to test stimuli (previously indifferent for the animal), leading to action by the effector even several days after cessation of the stimulation which formed the dominant. Stimulation of the paws in rabbits with rhythmic current impulses of threshold strength formed a rhythmic defensive dominant. The interaction (linkage) of sensorimotor cortex neuron activity in rabbits in the dominant focus was studied. The time sequences of the accumulation of intervals between linked spikes were analyzed as peaks on cross-correlation histograms (CCH). The frequencies of linked spikes or the intervals between them in the CCH peak during the 1-min analysis period were determined using “secondary” autocorrelation histograms (ACH). Further analysis was performed using selected peaks on secondary ACH, which dominated over the mean histogram level with significance p < 0.05. Formation of a rhythmic defensive dominant in the cerebral cortex was associated with the appearance of linked spikes not only at the stimulation rhythm (2 sec), but also at rhythms which were multiples of this (4, 6, and 8 sec). Neuron activity was recorded and analyzed after creation of a rhythmic dominant. At the beginning of each experiment (i.e., before presentation of test stimulation), linked spikes were dominated by the 2-sec rhythm. Repeated peaks on secondary ACH, providing evidence that linked activity was dominated by rhythms of 4, 6, and 8 sec, were absent or rare. Presentation of test stimuli showed a significant increase in the number of repeated peaks. It is suggested that subsequent exposure to test stimuli during the experiment enhanced the previously created latent focus of excitation, which became apparent as an increase in the complexity of the rhythm.

Neuron Activity before Behavioral Reactions and before Missed Reactions in a Defensive Dominant

The network relationships of neocortical neurons in rabbits with a defensive dominant in the CNS were studied in conditions of calm waking and during the intervals between presentations of light stimuli testing the dominant. Statistical analysis of spike trains extracted from multineuron traces allowed detection of differences in the functional organization of neurons in the excitation focus (sensorimotor cortex) and the representation area of the stimulus testing it (visual cortex) in calm waking before triggering of effector reactions and before missed reactions. These experiments yielded data on the different roles of sensorimotor cortex cells responding and not responding to light stimuli in the network activity of the areas of cortex studied.

Distribution in Time and Space of Linked Spikes in Closed Neural Circuits of the Sensorimotor Cortex in the Rabbit (a rhythmic defensive dominant)

Analysis of linked spike activity in simultaneously recorded neurons in the rabbit sensorimotor cortex identified 22 closed neural circuits consisting of three or four neurons. In experiments using a model of a defensive dominant, the distribution of linked spikes was analyzed in real time 1–3 weeks after imposition of a rhythmic (2 sec) activity on the rabbit. The analysis showed that events in which linked spikes in neuron pairs arose with 2-sec intervals could be displaced in time and space in one direction along the closed neuron circuit. Two-second intervals between linked spikes in neighboring pairs could be “conjugated,” i.e., the end of one interval in one pair was beginning of the 2-sec interval in the neighboring pair. “Conjugated” intervals of neighboring pairs could promote “pass-though” of information relating to the properties of the stimulus via the closed neuron circuit, thus completing a complete cycle of passage of the information through it. There could be several such cycles in a period of 1 min. The longest “passthrough” transfers lasted 10–12 sec. Complex variants of information transmission were identified, with not only pass-through transfers of the 2-sec interval from one neuron pair to another, but also repeat occurrences of linked spikes with this interval in any of the pairs constituting the circuit being analyzed. The longest transfers lasted 16 and 22 sec.

Dynamics of the Assimilation of an Imposed Rhythm by Neuron Assemblies in the Sensorimotor and Visual Cortical Areas of the Rabbit Brain

The linked activity of pairs of neurons in the sensorimotor and visual zones of the cortex was analyzed in naïve rabbits, rabbits being trained, and trained rabbits during formation of a latent rhythmic focus of excitation (defensive dominant) in the central nervous system. During formation of the dominant in the cortex, there was a progressive increase in the proportion of neuron pairs whose linked activity was dominated by the rhythm applied by the experimental stimulation. In the sensorimotor zone of the cortex of trained rabbits, as compared with untrained animals, there were significantly greater proportions of pairs of both close-lying and distant neurons, whose linked activity was dominated by the rhythm imposed during stimulation. In the visual zone of the cortex, a significantly greater proportion of these pairs was see only when distant neurons were studied. Analysis of the interactions of neurons in the sensorimotor and visual areas of the cortex also revealed training-associated increases in the numbers of pairs with the activity rhythm imposed during the experiment when the influences of sensorimotor cortex neurons on visual cortex neurons and vice versa were analyzed.