Interhemispheric asymmetry in rats differentiating figures by size

Motor alimentary conditioned reflex was elaborated in Wistar line rats to presentation of various pairs of figures, those of larger area serving as positive signals. In tests on animals with intact brain and with unilateral hemispheric cortical inactivation, new pairs of figures were used besides basic stimuli. The level of analysis in testing experiment was lower than normal: by 5.6% at intact brain, by 16.4%--at right hemisphere inactivation, by 36.4%--at left hemisphere inactivation. Elimination of the left hemisphere produced prolongation of the conditioned reaction time, signs of frustration and aftereffect. In conditions of right hemisphere inactivation the level of discrimination of figures depended on their specific properties and the side of presentation. Conclusion is made on dominating role of the left hemisphere in analysis of abstract and concrete characteristics of visual stimuli, in control of temporal, spatial and emotional characteristics of reactions in situations when considerable abstraction and distinguishing of generalizing invariant sign "more-less" is necessary for elaboration of the conditioned reflex.     

Interhemispheric motor asymmetry of conditioned feedback

The interhemispheric asymmetry and lateralization of motor functions, as applied to backward conditioning, was studied in two dogs that afterwards turned to be a right-hander and a left-hander. In the process of food-procuring instrumental conditioning it was revealed that one of the dogs predominantly used the right paw (with the dominance of the left hemisphere) and the second animal used the left paw (the right brain hemisphere dominated). The earliest signs of lateralization of the motor functions were observed in the backward conditioned connections (which had been formed earlier than the direct connections or direct conditioned reflexes). Consequently, the presence and sign of asymmetry can be predicted on the basis of manifestation of the backward connections observed at the early stages of acquisition of food-procuring behavior. The backward connections are strictly specific and have the same lateralization as the direct ones.     

Mouse genetic model for left-right hand usage: context, direction, norms of reaction, and memory.

Asymmetry of paw usage in the laboratory mouse is an experimental model for left-right asymmetry of hand usage. Given a set number of reaches into a centrally placed food tube (an unbiased or U-world test), individual mice exhibit a number of left and right paw reaches that is reliably expressed on retesting. Whereas different inbred strains appear to have equal numbers of individual mice with a left- or a right-preferred paw after a U-world test, there are significant differences among strains in the degree or strength of lateralization of the preferred paw. We report here a systematic series of tests of paw usage with naive mice and retests of the individuals in test chambers with the food tube biased to the left or to the right, contrasting the highly lateralized C57BL/6J and the very weakly lateralized (or ambilateral) CDS/Lay inbred strains and their (B6 x CDS) F1 generation. The results caused a shift in the paradigm of paw usage. There is an unexpected qualitative difference in paw usage between C57BL/6J and CDS/Lay. C57BL/6J is random in its left-right paw usage, but it is conditioned by the left or right direction of the initial biased-world test and by usage. CDS/Lay is constitutively equal-pawed, responds very little to direction of the test chamber, and is not conditioned by it. The probability of left-paw versus right-paw usage depends on both the genotype and the context of the test. The (B6 x CDS) F1 generation suggests that constitutive equal-paw usage of CDS/Lay is dominant to experience-conditioned paw usage of C57BL/6J. There is also an apparent quantitative difference between the very weakly lateralized (ambilateral) preferred paw usage in CDS/Lay and the highly lateralized preferred paw usage in C57BL/6J. The difference in degree of lateralization of preferred paw usage between the constitutively equal-pawed CDS/Lay strain and (B6 x CDS) F1 generation must originate from allelic differences at other gene loci between the CDS/Lay and C57BL/6J parental strains. The SWV and NOD/Lt strains were also assessed in asymmetrical tests because they were known to be weakly lateralized and similar to each other in a U-world test and to be significantly different from both C57BL/6J and CDS/Lay. SWV is experience-conditioned and weakly lateralized; NOD/Lt is constitutively equal-pawed and weakly lateralized. Further analysis will determine the genetic cause of the qualitative difference between constitutive equal-paw and experience-conditioned paw usage and the genetic cause of the quantitative differences in degree of lateralization of the preferred paw within each type of paw usage.     

Effect of cadmium chloride on the processes of learning and memory in rats

Intraperitoneal injection of cadmium chloride (4 mg/kg) to rats before elaboration or reproduction of two-way avoidance conditioned reflex (TACR) disturbs both these processes. Deterioration of elaboration does not affect connections fixation and their subsequent reproduction. Injection of the substance before the elaboration of passive avoidance conditioned reflex (PACR) depresses elaboration and consolidation. Injection of cadmium chloride before testing of PACR preservation does not influence the processes of engrams reproduction. The observed disturbances cannot be connected with changes of animals motor activity.     

Characteristics of the perception and imagination of emotions in patients with focal brain pathology

Voluntary components of the emotion perception were shown to be related to the left hemisphere temporal area in patients with focal lesions of postero-frontal and temporal areas of both hemispheres, whereas the involuntary components required involvement of the right hemisphere temporal area. The voluntary components of the emotion reproduction are associated with involvement of the left hemisphere postero-frontal area, whereas involuntary components of perception are related to work of the right hemisphere postero-frontal area. The data obtained suggest that the voluntary (conscious) recognition and reproduction of emotions are mainly related to the sensory and motor speech centres of the left hemisphere, whereas involuntary those involve symmetrical areas of the opposite hemisphere.     

The dynamics of forming an active defensive reflex in cats]

Active defensive reflexes were elaborated in cats with pain stimulations of the forepaw by means of an electrical pricking device with a target attached to it. The elaboration was carried out during action of a flickering light used for the convenience of the EEG analysis. Repeated pain stimulation led to elaboration of an aggressive attacking reaction, chiefly manifested in the paw striking the target. At the beginning of the elaboration, passive-defensive reactions were manifest, which did not completely disappear even after formation of a stable attacking reflex. Two types of active defensive reflexes were elaborated: A-type reflex which helped the animal to get rid of the pain stimulation at the very beginning; B-type reflex which prevented the pain stimulation. The difference beteween these two types is discussed.     

Levels of consciousness and levels of activation

In the paper Pavlov's idea is used about "the bright spot of consciousness" as a zone of increased excitability which moves over the cerebral cortex. Zone of increased activation is revealed migrating from the frontal parts of the left hemisphere to the occipital parts of the right hemisphere. By means of various methods (record of amplitude and latency of the visual evoked responses, frequency and amplitude of the dominant rhythm, spectral-coherent analysis of the electroencephalogram) the activation of focus in the cerebral cortex was singled out, which moved, depending on the novelty, complication and degree of automatization of the task, from the frontal parts of the left hemisphere to the occipital parts of the right hemisphere. A parallel is drawn between Pavlov's hypothesis on the focus of consciousness as foci of increased brain activity, and revealed foci of activation. The conclusion is made about fluctuations of consciousness level as a factor which is in the basis of activation focus migration.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.     

Hemispheric lateralization of visuo-spatial function in man

Two parts of a geometrical figure are consecutively presented to healthy adult subjects in the left and right visual fields; the subjects have to compare them mentally and to decide whether these parts form a standard figure or not. Correctness of the reaction is controlled by a computer which lights up on the screen the words "good" or "error". The number of correct decisions of this visual-spatial task does not depend on the hemisphere to which information is addressed. The reaction time is substantially shorter if the information comes "directly" to the right hemisphere. Due to better training in the left hemisphere interhemispheric difference in reaction time gradually disappears in repeated tests. Training to mental "constructing" takes place only in the tests following positive feedback stimulus. Analysis of amplitude-temporal parameters of P300 wave shows that at correct decision of the visual-spatial task the level of activation in the right hemisphere is higher than in the left one.     

"Animal hypnosis" and defensive dominant,behavioral aspect

A stationary excitation focus produced in the sensorimotor cortex of a rabbit by rhythmic electrodermal paw stimulation was manifested in the reaction to a testing sound stimulus earlier indifferent for the animal. Regardless of the stimulated paw (left or right), reactions to the testing stimuli appeared approximately in the equal percent of cases (70.7% and 71.5%, respectively). After a single-trial induction of the "animal hypnosis" state, it was difficult to produce the dominant focus by simulation of the left paw, whereas the results of the right-paw stimulation did not differ from those obtained during control stimulation. Consequently, the influence of hypnosis on defensive stationary excitation foci in different hemispheres was not the same.     

Interhemispheric asymmetry of "emotional resonance" in the rat

Hemispheric asymmetry of "emotional resonance" elaborated by the method of P.V. Simonov was studied in Wistar rats. Inactivation of hemispheres was carried out by means of spreading depression. When using as "victims" and "recipients" the animals of the same sex, lateralization of emotional resonance was found to depend upon the velocity of reaction elaboration. In rats rapidly elaborating avoidance reaction the right hemisphere dominated during its performance and so did the left one in animals learning after additional training. When using the animals of different sex as "victims" and "recipients", the right hemisphere dominated in "emotional resonance" performance. Hemispheric asymmetry of "emotional" resonance was more expressed in males than in females.     

Increased regularity of activity of cortical neurons in learning due to disinhibitory effect of reinforcement

This paper reviews the author's studies on neurophysiologic mechanisms of conditioned reflex learning. Electroencephalograms, evoked potentials, activity of neocortical and hippocampal neurons and the rabbits' behavior in the course of elaboration of defensive and inhibitory conditioned reflexes to light flashes have been recorded. Electric shock (ECS) applied to the paw served as reinforcement. The study demonstrated three types of reinforcement effect on the activity of cortical neurons: activating, disinhibitory, and inhibitory. EEG activation due to reinforcement is accompanied by a change in phasic cortical neuronal activity from chaotic or irregular, typical of rest or inhibition, to regular tonic discharges (in neocortex and hippocampus) and group discharges in the stress rhythm, 5-7 Hz in the hippocampus. Following a number of conditioning trials, the effect of reinforcement is simulated by the effect of a conditioned stimulus. With EEG activation and increased regularity in impulses, facilitation of motor reactions is observed.     

Asymmetry in the dopamine content in the nucleus accumbens and the motor preference in rats

A number of published studies reported a correlation between the paw preference in mice and asymmetry of tissue concentrations of dopamine (DA) and DA metabolites measured in the nucleus accumbens (NAcb) the DA concentration being higher in the nucleus ipsylateral to a preferred paw. This study aimed to investigate whether such asymmetry existed in rats. The paw preference was defined by reaching into a small horizontal tube for a food pellet. Tissue concentration of DA was measured by high-performance liquid chromatography with electrochemical detection. It was shown that the DA concentration in the left NAcb was significantly higher in "left-handed" rats than in "right-handed" animals. Within the group of "right-handers", the DA concentration was significantly higher in the right NAcb than in the left NAcb. The results confirm in part the experimental data obtained in mice and support the hypothesis that the paw preference is paralleled by elevated tissue DA in the ipsylateral NAcb of rodents.     

Models of learning based on the plastic properties of the "placing reaction" in cats]

A possibility of functional reorganization of initial sensorimotor connections of the forepaw has been shown on seven cats. The main initial relationships between the afferent tactile input and motor output for the ulnar joint of the cat forepaw are as follows: tactile stimulation of the dorsal surface of the paw produces a flexion in the ulnar joint ("placing reaction"), and that of the ventral surface, an extension of the paw in the ulnar joint ("magnetic reflex"); simultaneous tactile stimulation of the ventral surface of the paw blocks the "placing reaction" evoked by a touch of the dorsal side. Extinction was produced of the above unconditioned connections and elaboration of a new "cross" connection consisting in that tactile stimulation of the ventral side of the paw resulted in flexion in the ulnar joint.     

The thermal activity of the rabbit brain during the interaction of "animal hypnosis" and of the hunger dominant]

The character of interaction between two dominant foci (motivation hunger dominant and "animal hypnosis") which had been formed in the rabbit brain was ambiguous: the foci could either function simultaneously or compete. In the first case, summation food reactions were observed when the hunger dominant was tested during a hypnotic episode against the background of deep and continuous hypnotic state. Brain thermal activity was asymmetric the temperature being higher in the parieto-occipital areas of the left hemisphere. If the hypnosis inhibited the hunger dominant, summation reactions were absent and the brain temperature was higher in the parieto-occipital areas of the right hemisphere. In cases when despite the repeated immobilization sessions the hunger dominant prevented from induction of hypnosis, the left-hemisphere thermal dominance persisted against the background of general brain cooling.     

Thermoencephaloscopy of brain responses to emotionally significant visual stimuli in depressive patients

The thermoencephaloscopic study of patients with reactive depression during exposure to emotionally significant visual stimuli detected a functional change in the state of the frontal associative area of the right hemisphere and the parietal associative area of the left hemisphere and the activation of the left temporal area, closely related to the limbic system. The data obtained may be used for the elaboration of new methods of diagnosis and therapy of reactive depressions.     

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.     

Interhemispheric relations of prefrontal cortical neurons in rats during emotional stimulation of increasing intensity

Unit activity of the prefrontal cortex of the right and left brain hemispheres of rats was recorded during intracranial stimulation of emotionally positive and negative brain structures. The neurons were divided according to their reaction to a change in food motivation: cells that decrease (M-neurons) and cells that increase their firing frequencies (R-neurons) after feeding. Three levels of stimulation current intensity were used. When stimuli of subthreshold intensity (evoking the behavioral reaction of smelling) were applied, the recorded neuronal activity was higher in the left hemisphere. During threshold emotionally positive or negative stimulation (producing approach behavior or freezing, respectively), activity of M-neurons was higher in the right hemisphere, whereas the left-side R-neurons were more active than the right-side ones. During strong emotionally positive stimulation producing self-stimulation, the firing frequency of both groups of neurons was higher in the left hemisphere. Strong emotionally negative stimulation that evoked behavioral avoidance to a greater extent activated the right hemisphere.     

Effects of thymosin and B-activin on lateralization of sensomotor control in rats

Characteristics of regulatory effects of B-activin and thymosin (fraction 5) on the activity of right and left hemispheres were studied in rats. The results obtained were estimated basing on the analysis of the following components of food-searching behavior: lateralization of a single conditioned-reflex response; preference of right or left paw; spontaneous rotations. Opposite effects of thymosin and B-activin were found at different stages of the food-searching behavior. Thymosin activated structures of the left hemisphere. A conclusion is made on the possibility of application of these drugs for targeted influencing the balance of intra-hemispheric activity in the brain functional pathology and during the compensatory process.     

Changes in dry weight of pyramidal cell nuclei in the motor cortex during local motor-food conditioning

The formation of a local motor-food conditioned reflex in rats, consisting of pressing on a level with the unpreferred paw, in one session led to a decrease in dry weight of the large pyramidal cell nuclei in the area of representation of that paw in the motor cortex. Frequent repetition of the local motor-food conditioned reflex consisting of pressing on the level with the preferred paw was not accompanied by any such changes. It is suggested that changes in dry weight of the large pyramidal cell nuclei in the area of representation of the unpreferred paw are due to involvement of these neurons in the formation of the new motor coordination (the local conditioned reflex).