Interhemispheric asymmetry in the functional organization of the prefrontal cortex in animals of different typologic groups

Rats allocated to groups by the method of "emotional resonance": rats which did and did not escape crying of a partner (A- and E-groups, respectively). Unit activity in the right and left prefrontal brain cortex (PFC) was recorded in these rats. The recorded neurons neurons were divided in two groups according to their reaction to a change in the level of food motivation. The so-called D-neurons decreased their activity after feeding of animals after a 24-hour food deprivation and the other group (I-neurons) increased its firing rate rate in this situation. It was shown that hemispheric distributions of D- and I-neurons are different in selected rat groups. In E-rats the I-neurons substantially predominated in the left hemisphere, whereas the D-neurons were more frequently recorded in the right one. No such asymmetry was observed in A-group of rats. During intracranial stimulation of emotionally positive brain structures I-neurons increased their firing rate, predominantly, in the left hemisphere, whereas during intracranial emotionally negative stimulation activation of the D-neurons predominated at the right. Features of the observed functional interhemispheric asymmetry of prefrontal cortex in A- and E-groups of rats were explained by differences in the interaction between hemispheres and dissimilar activation control.     

The asymmetry of cerebral hemispheric activity in dogs in a state of quiet wakefulness under the action of sensory stimuli and food deprivation]

The EEG was recorded in four dogs from symmetrical cortical areas of the left and right brain hemispheres. Activation foci were determined by the maximal values of the mean frequency of EEG oscillations and coherence function. In the background experiments, the hemispheric activation asymmetry was observed in all dogs. The individual differences were in the frequency ranges, which were asymmetrically localized. In three dogs the coherence level was significantly more frequently higher in the right hemisphere than in the left one, in one dog the opposite relations were observed. These differences in activation foci localization were correlated with different tactics of choice between two feeders under conditions of free behavior. Under the action of external stimuli, changes in hemispheric activation were observed, predominantly, in the corresponding projection areas, and at the shifts of food excitability they were localized in symmetrical frontal areas. The results suggest that the left hemisphere becomes more activated during the first presentations of indifferent stimuli, i.e., during the development of the reaction to novelty, and under conditions of food deprivation, which rises the level of brain activation.     

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.     

Recognition of visual images by separate hemispheres in conditions of masked blocking of interhemispheric transmission

The subjects learned to recognize three figures presented in the left visual hemifield and three figures presented in the right visual hemifield. During presentation of a stimulus, the contralateral hemifield was overlapped by a mask. After the training, recognition of all six figures presented in the right and left visual hemifields, was compared. Each hemisphere recognizes figures which were learned in the corresponding visual hemifield, but the recognition of figures learned in the opposite visual hemifield was poor. Thus, the ability of the hemispheres to act separately in recognizing different sets of visual images, was established.     

Rearrangement of the Prefrontal Cortex Neural Activity in Both Hemispheres during Learning

Neuronal activity of both right and left hemispheres of the rat prefrontal brain cortex was recorded in the two-ring maze during animal learning to operate in response to signals. At the beginning of learning, pairwise comparison of neural activity that accompanied correct and incorrect choice of the right and left sides showed significant differences in the left hemisphere and the lack of differences in the right one. With increasing percentage of correct choices during a session of learning, the differences in neuronal responses appeared in the right hemispheres and were reduced in the left one. The opposite trends in rearrangement of the total impulse activity are believed to be related to different roles of hemispheres in the construction of the internal behavioral model.     

Functional asymmerty of the brain and emotions

Different kinds of emotional phenomena are related in a different way with the workings of the left and right hemispheres of the brain. Emotional reactions (phasic emotions), which appear on the basis of a cognitive loading (mental representation, recognition, play, prognostication, watching movies, reading of emotionally colored texts or separate words and so on) and which are tested with the help of electrophysiological methods, activate different regions of the left and right hemispheres of the brain depending on the complexity and novelty of emotiogenic situations as well as on the degree of subject's emotional tension. The tonic emotions individual background-mood, on which depends the emotional estimation (negative of positive) of the presented stimuli or events, are determined mostly by a prolonged, relatively stable, tonic activation of each hemisphere connected with subjects' individual characteristics. The predominance of the left hemisphere activity creates positive emotional background, whereas the predominance of the right hemisphere creates negative background.     

Effects of intra-amygdala injection of GABA(A)-receptor agonist and antagonist on behavior of active and passive rabbits in negative emotional situations

The effects of right-side or left-side intra-amygdala injections of the GABA(A)-receptor agonist muscimol hydrobromide (0.1 microg/1 microl) and antagonist bicuculline methiodide (0.05, 0.1, 0.5 microg/1 microl) on the behavior of active and passive rabbits were studied in open field, light-dark test and during presentation of emotionally significant stimuli. The effect of compounds injection was differed in active and passive rabbits. The active rabbits were more sensitive to bicuculline injection and the passive rabbits to muscimol administration. Bicuculline induced anxiolytic-like effects on the active animals in open field, light-dark test and motor-activating effects during emotionally significant stimuli. Muscimol induced anxiolytic-like effects on the passive rabbits and sedative effects on the both groups of rabbits. The differences in effectiveness of right-side and left-side intra-amygdala injections on behavior of rabbits were revealed: more powerful changes were during injection of bicuculline in left and muscimol in right amygdala. Anxiolytic-like effects were revealed during injection of bicuculline into left amygdala of active rabbits and muscimol into right amygdala of passive rabbits. These findings indicate that there are individual-typological and interhemispheric differences in functioning of GABAergic system of amygdala.     

Asymmetry of aging of the large hemispheres of the rat brain

The dynamics of the accumulation of free-radical oxidation products in the brain hemispheres of rats in rate ontogenesis was studied. Multiphase changes in the concentration of products in the right and left hemispheres in different age groups were registered. Significant differences in the contents of hydroperoxides, Schiff's bases of phospholipids and lipofuscin in brain hemispheres revealed, which correlates with different rate of ageing of hemispheres.     

Bilateral Skin Conductance Responses to Emotional Faces

Skin conductance responses (SCR) measure objective arousal in response to emotionally-relevant stimuli. Central nervous system influence on SCR is exerted differentially by the two hemispheres. Differences between SCR recordings from the left and right hands may therefore be expected. This study focused on emotionally expressive faces, known to be processed differently by the two hemispheres. Faces depicting neutral, happy, sad, angry, fearful or disgusted expressions were presented in two tasks, one with an explicit emotion judgment and the other with an age judgment. We found stronger responses to sad and happy faces compared with neutral from the left hand during the implicit task, and stronger responses to negative emotions compared with neutral from the right hand during the explicit task. Our results suggest that basic social stimuli generate distinct responses on the two hands, no doubt related to the lateralization of social function in the brain.     

Linear Blood Velocity in Arteries of the Brain Hemispheres in Left-Handers and Right-Handers during Hypoxia

Transcranial Doppler ultrasonography was used to measure the linear blood velocity (LBV) in the middle cerebral artery (MCA) of the right and left hemispheres in right-handers and left-handers who were breathing a gas mixture with 10% oxygen through a mask at normal barometric pressure. No interhemispheric differences were found in left-handers before hypoxia. The maximum systolic velocity was higher in the MCA of the left hemisphere in right-handers. Left-handers had a higher LBV in the right hemisphere than did right-handers. LBV in the MCA of both hemispheres increased in both left-handers and right-handers as a result of hypoxia. Aggravation of hypoxia caused a decrease in LBV in the left hemisphere in right-handers.     

Lateral effects of emotional stimulation on verbal memory processes in men and women

Effects of short-term changes in emotional state of men and women on hemispheric organization of verbal memory processes were studied in the model of emotional electrodermal stimulation. Retrieval of dichotically presented lists of words was analyzed. The lists of words included pairs of emotionally neutral word and pairs combined of a neutral and emotional or both emotional words. There were no gender differences in the immediate retrieval of the words. Electrodermal stimulation prior to presentation of list of word resulted in a lateralized reduction of the immediate report of neutral words presented to the right ear and of emotional words presented to the left ear. Gender-related differences were shown in the delayed retrieval. In women, the stimulation applied before word presentation induced a decrease in delayed retrieval of left-ear emotional words. In men, the stimulation applied after the word presentation improved the retrieval of word lists independently of the side of presentation. Mechanisms of gender-related differences in interhemispheric interaction in verbal memory processes are discussed.     

The Lateralizer: a tool for students to explore the divided brain

Despite a profusion of popular misinformation about the left brain and right brain, there are functional differences between the left and right cerebral hemispheres in humans. Evidence from split-brain patients, individuals with unilateral brain damage, and neuroimaging studies suggest that each hemisphere may be specialized for certain cognitive processes. One way to easily explore these hemispheric asymmetries is with the divided visual field technique, where visual stimuli are presented on either the left or right side of the visual field and task performance is compared between these two conditions; any behavioral differences between the left and right visual fields may be interpreted as evidence for functional asymmetries between the left and right cerebral hemispheres. We developed a simple software package that implements the divided visual field technique, called the Lateralizer, and introduced this experimental approach as a problem-based learning module in a lower-division research methods course. Second-year undergraduate students used the Lateralizer to experimentally challenge and explore theories of the differences between the left and right cerebral hemispheres. Measured learning outcomes after active exploration with the Lateralizer, including new knowledge of brain anatomy and connectivity, were on par with those observed in an upper-division lecture course. Moreover, the project added to the students' research skill sets and seemed to foster an appreciation of the link between brain anatomy and function.     

Asymmetry of the cerebral hemispheres during comparison of paired visual stimuli

In conditions of tachistoscopic presentation of visual stimuli, healthy (male and female) right-handed subjects carried out a paired comparison of the stimuli presented unilaterally and in the center of the visual field. In case of recognition of images of words and objects, the number of correct answers and motor reaction time usually did not significantly differ at two interstimuli intervals (1 and 10 s). In comparing images of faces, there also were no differences by the number of reactions, and the reaction time was less at the intervals of 1 s. The left hemisphere dominated at the identification of words and female faces, the right one--at the recognition of male faces. When the right visual field was stimulated images of various classes were recognized more differentially than at the stimulation of the left visual field. The male subjects had more prominent interhemispheric differences than the females. The increase of the interstimuli interval from 1 to 10 s brought to a weakening of the functional interhemispheric asymmetry and decreasing of the differences between the male and female subjects. The obtained data show that in the processes connected with short-time memory, functional interhemispheric asymmetry is basically formed at the initial stages of the information processing.     

Free Fatty Acid Content and Release Kinetics as Manifestations of Cerebral Lateralization in Mouse Brain

Free fatty acid (FFA) content was analyzed in mouse cerebral hemispheres and cerebellum under basal and postdecapitative ischemic conditions. Total FFA content immediately after decapitation (2 s) was about two-fold higher in the left hemisphere than in the right. Marked dissimilarities between hemispheres were also apparent when FFA levels were measured during short periods of ischemia. Whereas in the right side a significant FFA release took place as early as 10 s, no accumulation was detected in the left in the 2-20 s interval. The highest rates of total fatty acid release occurred in the 20-30 s interval in both hemispheres and decreased afterwards (3 min). Individual FFA, especially stearate and arachidonate, differed in their rates of production, the right cerebral hemisphere being more active in releasing arachidonic acid. In cerebellum, FFA levels were lower and accumulation was slower than in cerebrum in both intervals. When subjected to 3 min ischemia, the same difference in FFA levels between right and left hemispheres (50%) was observed in heads kept at 20 or 30 degrees C. The differences between hemispheres are interpreted as manifestations of an inherent lateralization in the regulation of acylation-deacylation reactions of complex lipids.     

Neuronal activity in the prefrontal cortex in rats with various typological features during emotional affect

Unit activity in the right and left prefrontal cortex was recorded in male Wistar rats after testing by the emotional resonance technique. Rats were divided in two groups by their reaction to the suffering cry of a partner. Rats from the group A ("altruists") escaped partner's crying, and those from the group E ("egoists") did not. Activity of neurons was analyzed in hungry rats, after feeding, during intracranial emotionally positive and negative stimulation, and during crying of the rat partner. Some differences in neural activity between A and E groups were revealed. In the hungry state the rate of neuronal discharges was higher in the A group. In both groups of animals the positive emotional stimulation was accompanied by more intensive neuronal reaction that the negative stimulation, but in the E group increase in the rate of neuronal discharges in both hemispheres was significantly more pronounced. Negative stimulation produced in both groups a significantly greater activation in the left hemisphere than in the right one while during the positive stimulation the neural activity was more intensive in the left hemisphere. The neuronal reaction to partner's crying was significantly higher in the A group in both hemispheres, while the neuronal activity in E group did not significantly change.     

Gender differences in EEG coherence during memorization of dichotically and monaurally presented verbal stimuli

Gender differences in changes of coherence values in the theta and alpha frequency bands during encoding of dichotically and monaurally presented verbal information were studied. Right-handed students (14 male and 14 female subjects) participated in experiments. The EEG was recorded from 16 electrodes placed at homologous sites of the left and the right hemispheres. In male subjects, numerous differences in coherence values between conditions of dichotical and monaural word presentation were found in the theta2- and alpha1-bands, in females, the differences were most pronounced in the theta1- and theta2-frequency bands. Numerous differences in coherence values differentiated between dichotic and left-sided monaural presentations in males and between dichotic and right-sided monaural presentations in females. As compared to dichotic presentation, in condition of the monaural presentation, higher coherence values were observed in men and lower in women. The features of gender differences in frequency-spatial patterns of changes in EEG coherence values under conditions of bilaterally and unilaterally directed attention in male and female groups may testify that female subjects predominantly use right-hemispheric processing strategy, whereas male subjects use, mainly, left-hemispheric strategy for selection and memorization of concrete nouns.     

Electrophysiologic analysis of the process of recognizing target and non-target stimuli in healthy and oligophrenic children

In an automatized experiment, with a computer on line, amplitude-temporal parameters of evoked potentials (EPs) to purposive and non-purposive stimuli (digits), were analyzed in normal and mental retarded children. At unilateral stimuli presentation to the left or right visual half-fields EPs were recorded simultaneously in projection, TPO, parietal and central areas of the left and right hemispheres. It has been shown that in normal children, differential involvement of projection and associative structures in the analysis of sensory information takes place in both hemispheres. The amplitudes of most EP components in the range of 100-400 ms to the purposive stimuli are higher than to the non-purposive ones. Considerable similarity of EPs developing in response to ipsi- and contralateral stimulations of visual fields ("direct" and "transmitted" EP) is observed. In mental retarded children significant changes are revealed in intra- and interhemisphere organization of the process of perception of purposive and non-purposive stimuli. In the right hemisphere structures there are no differential EP reactions to the two types of stimuli. Significant, in comparison with the norm, prolongation of the latencies of most EP components is noted, especially in the structures of the left hemisphere, to the purposive stimuli. In the process of perception, changes are seen of the integration of functions of both hemispheres. The totality of disturbances of systemic brain organization at perceptive activity in mental retarded children may reflect neurophysiological mechanisms of mental deficiency.     

Basic principles of structural asymmetry of cortex formations in the human brain

Studying the cytoarchitectonical asymmetry of human brain cortex requires using the new approaches and modern quantitative methods. One of the promising ways is analyzing relation between the macroscopic and neuronal structure of the brain. The present article contains original data of histological and morphological studies. The authors develop the concept of different degree of expression of asymmetry in the cortex formations of left and right hemispheres. The data on the principal differences of topography and types of structure of fissure and gyrus in different brain hemispheres are presented. Results of the analysis carried out enable one to show the basic criteria of peculiarities of cytoarchitecture of human brain cortex in the left and right hemispheres.