Interrelations of the cerebral hemispheres in the cat in early stages of ontogeny

Multiple recording of transcallosal responses (TCRs) from different cortex areas has been carried out by means of acute experiments with immobilized and anesthetized kittens at the age of 1 to 30 days after birth. Homotopical TCRs in kittens at the age of 2-15 days appear earlier, are presented wider and reveal features of a greater maturity configuration and of amplitudinal-temporal parameters in association zone (parietal and sensorimotor) in comparison with projection zones (somatosensory, visual and auditory). Interhemispheric interrelations in association cortex of kittens are carried out not only by means of callosal but extracallosal system. In the course of animal developing in the parietal cortex the drain of the surface-positive oscillation moves from V to III layer and the drain of the surface-negative deviation remains at the level of II-III layers. The late component is registered up to the depth of III-IV layers, having the drain in I-II layers. In sensorimotor cortex the surface-negative oscillation has the drain in I-II layers, surface-positive--in III and V--VI layers. The interhemispheric asymmetry emerging from the moment of responses appearance is peculiar to TCRs of projection and association zones. In the first month of the postnatal development the asymmetry of positive and negative TCR oscillation amplitude has an individual character in sensorimotor cortex and a specific one--in parietal. The temporal parameters of TCR in association areas of the left hemisphere cortex are significantly shorter than of the right one. The data given testify to the possibility of interhemispheric interrelation realization and the presence of interhemispheric asymmetry in cat's brain on the early stages of postnatal ontogenesis.     

Ontogenesis of the asymmetry of transcallosal responses in the cat parietal cortex

In acute experiments on 2-24 days old immobilized kittens and adult cats, studies have been made on the development of functional interhemispheric asymmetry of homotopical transcallosal responses in the parietal cortex. It was found that the number of animals with evident asymmetry increases with age. Alongside, with respect to such characters as asymmetry coefficient, mean amplitude of components of transcallosal components and the ratio of zones of direct and inverse domination, the increase in functional interhemispheric asymmetry was observed during the second week of postnatal life of kittens, which was accompanied by the inversion of its sign; in adult cats, the decrease in the asymmetry up to its complete absence was found. The data obtained are discussed with respect to peculiarities of the development and functional properties of the associative parietal cortex in cats.     

Sexual differences in the interhemispheric asymmetry of the transcallosal responses of the associative areas in the cat neocortex

Sex differences of hemisphere asymmetry of homo- and heterotopic transcallosal responses in association cortex of 48 cats (24 male and 24 female) immobilized by tubocurarine have been studied by means of topographic EPs recordings in both hemispheres. In males left hemisphere dominates by the amplitude of homotopic and positive wave of heterotopic EPs and right hemisphere dominates by the amplitude of negative wave of heterotopic sensorimotor cortex EPs. The individual asymmetry of EPs has been observed in sensomotor cortex of females and in parietal cortex of animals of both sex. The interhemispheric asymmetry is expressed distinctly in females than in males. It is concluded that sex dimorphism is present in functional organization of associative system of (callosal and intracortical) connections in cat's neocortex projection and association areas which means its more expressed hemisphere lateralization in males with more expressed interhemispheric asymmetry of functional transcallosal connections in females.     

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.     

Functional Asymmetry of the Brain and Ignoring of the Environment

Manifestations of functional asymmetry of human cerebral cortex at spatial orientation in the visual and auditory systems are considered. Disorder of the right hemisphere activity leads to two main interrelated disorders: ignoring of a portion of the extrapersonal space on the left and compression of this space on the right. The revealed disorders are considered as a result of suppression of activity of brain structures (first of all, of the parietal area of the right cortex) that form body scheme (the reference level at the spatial orientation). The suggestion is made about causes of ignoring of the external sensory space in disturbances of the right parietal cortex area. Role of the right hemisphere in other possible forms of ignoring of the external space is considered.     

Anatomical brain asymmetry in monkeys: frontal, temporoparietal, and limbic cortex in Macaca

Measurements evaluating possible cerebral hemispheric asymmetries were taken by hand on frontal, parietal, and temporal cortex on 60 formalin-fixed Macaca mulatta and Macaca fascicularis brain specimens. No statistically significant (P less than 0.05) right/left side differences in the mean length of four sulci in visual-processing areas of the cortex were found. The sulcus adjacent to the region cytoarchitecturally homologous to the motor speech area in the human brain did not show pronounced asymmetry. In both species, however, a small parietal lobe sulcus showed greater development on the left hemisphere than in the right. In measurements made using digital planimetry, right/left side differences in the area of the dorsal cingulate gyrus were not found. Behavioral evidence suggests that monkeys do not exhibit a consistent pattern of cerebral dominance for functions associated with most of these regions of the brain.     

Left and right brain hemispheres in the regulation of pain sensitivity biorhythms in mice during stress

The foot-shock effects on ultradian and circadian rhythms of pain sensitivity in the SHR mice were studied after unilateral brain cortex hemisphere inactivation by means of the Leao spreading depression. Under acute painful stress, the left hemisphere partially loses its synchronizing effect on circadian rhythm and supports the 12-hour and particularly 6-hour periodicities. The left hemisphere effect dominates in intact animals under stress. The right hemisphere under the same conditions mainly loses its activating effect on circadian rhythm and supports the 8- and 16-hour periodicities. The right hemisphere effect dominates in animals under stress operated 2-3 days prior to the experiment.     

The hemispheric lateralization of the recognition of noisy visual stimuli in man

At tachistoscopic unilateral presentation of noisy visual stimuli and application of "yes-no" method in man predominance was found of the right hemisphere by the number and "yes" reaction time and of the left hemisphere by the number of responses "no". At verbal mnemic load preceding the presentation of visual patterns the left hemisphere asymmetry was observed by the number of "yes" responses and reactions time of both types. FMA was more clearly expressed in men in the first case and in women--in the second one. In more difficult conditions of recognition of several types of patterns, FMA was noticed mainly in women: initial left hemisphere advantage during the increase of the disturbance was changed to the right hemispheric one and appeared again. Preferential participation of the right hemisphere in singling out of the visual signal from noise is supposed. Possibility of the left hemispheric asymmetry manifestation was determined by the specificity and complexity of the visual task, by the level of the disturbance, presentation of competitive task and sexual composition of the group.     

Quantitative characteristics of cells formed during early postnatal ontogenesis in the cytoarchitectonic layers of the parietal region of the cortex in normal mice and following brain injuries]

By means of computer analysis, size distribution of neurons and glial cells together with the label of 3H-thymidin labelled cells were studied in cytoarchitectonic layers of the field 1 in the mouse parietal cortex injected with the isotope on the 5th day of life and killed 1 month later. In some animals, 3 days before 3H-thymidin injection, the parietal region in the right hemisphere was perforated. The labelled cells were subdivided into 2 groups according to their size: astrocytes (A) and small gliocytes (mg). Labelled A and mg were stated to be rather evenly distributed along the cytoarchitectonic layers in the field 1. The trauma performed resulted in increasing amount of the labelled A and MG in the operated hemisphere. Uniformity in distribution of the labelled A and mg, occupying the position of satellites, did not change considerably at the trauma, in spite of general quantitative increase of the labelled glial cells. One month after the trauma, body dimentions of the mice labelled with A and mg did not considerably differ from those of intact animals, while the size of nerve cells increased. Thus, neurons in the parietal cortex of a growing brain respond to brain trauma with hypertrophy of cell bodies, and glial populations--with increase of their number.     

Hemispheric asymmetry of the space-motion component of a food-conditioned motor reflex

The preference of movement direction in the process of motor food conditioned reaction has been investigated in rats with intact brain and after unilateral cortical inactivation. It was shown that the degree of motorspatial preference diminished with the maturation of reaction. At the high level of differentiation the valid preference was shown only in 38% of animals investigated but it was absent in the rest of animals. After inactivation of right hemisphere cortex left-side preference occurred in the presence as well as in the absence of the original preference. Inactivation of the left hemisphere cortex is less significant; it influences the original preference of movement direction permanently affecting those animals which normally had evident preference. It is concluded that the right hemisphere cortex plays dominant part in both sensor and motorspatial components of motor food conditioned reaction. It is supposed that the definite relationship exists between the degree of preference of movement direction and the functional asymmetry of cerebral hemispheres.     

The role of the frontal cortex of the left and right hemispheres in regulating the intraspecific interaction of rats with differing zoosocial experience

By means of the analysis of probabilistic ethological structures of the intraspecies rats behaviour in the test "stranger-resident" and by the method of isolated destruction of the frontal cortex or the left and right hemispheres,--it is established that the frontal cortex of the left hemisphere regulates the intraspecies sociability and keeps it on a certain level, because the change (increase) of the intraspecies sociability is observed only at the unilateral destruction of the left frontal cortex. Isolation from the relatives in early ontogenesis leads to the loss of regulating influence of the left frontal cortex on the intraspecies sociability. In isolated animals the frontal cortex of the left hemisphere regulates the level and probability of the appearance of aggression. The right hemisphere ensures the adequate inclusion of the aggression in the probabilistic ethological structure of the total intraspecies behaviour; at its damage the forms appear of an adequate pathological aggression, and connection is lost between the elements of aggressive behaviour and the acts of intraspecies sociability.     

Evoked potentials in the parietal cortex in response to stimulation of the posterolateral nucleus of the thalamus in kittens of different ages

In kittens of the first month of postnatal life, studies have been made of the evoked potentials in the parietal cortex elicited by stimulation of the posterior lateral thalamic nuclei. It is suggested that within the first days of life the EPs result mainly from the electrical activity of the deep (V-VI) layers of the cortex. This suggestion is confirmed by a significant increase in the velocity of the rising phase and the decrease of the duration of the EPs in the deep layers in newborn animals, as well as partial inversion of the negative wave of the EP at the level of these layers in 1-week kittens. Total depth of the median layers in 1-week kittens is twice less than that in 1 month old ones. To the end of the 2nd week, the input of the activity of the median layers into total activity increases: the focus of partial inversion of the negative wave of the EPs is translocated upward to the border of layers II-III. In 1-month kittens, the general pattern of the EPs in the parietal cortex is the same as in adult cats.     

Origination and development of sensorimotor, associative and transcallosal responses in kittens in ontogeny

In acute experiments on 3-30-day kittens, recording the evoked potentials, studies have been made on the development and maturation of sensorimotor parietal associative and transcallosal responses (TCR). At early ontogenetic stages, these TCR are presented by single negative oscillation, strictly localized, with a large latent period and long duration. During postnatal life, the duration of the latent period decreases, whereas the area of the evoked potentials increases. Investigation of the electrical responses in focus of maximum activity in sensorimotor and parietal associative regions in kittens of all age groups revealed earlier activation of the projectional areas and later maturation of the associative inputs.     

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.     

Microstructural Damage of the Posterior Corpus Callosum Contributes to the Clinical Severity of Neglect

One theory to account for neglect symptoms in patients with right focal damage invokes a release of inhibition of the right parietal cortex over the left parieto-frontal circuits, by disconnection mechanism. This theory is supported by transcranial magnetic stimulation studies showing the existence of asymmetric inhibitory interactions between the left and right posterior parietal cortex, with a right hemispheric advantage. These inhibitory mechanisms are mediated by direct transcallosal projections located in the posterior portions of the corpus callosum. The current study, using diffusion imaging and tract-based spatial statistics (TBSS), aims at assessing, in a data-driven fashion, the contribution of structural disconnection between hemispheres in determining the presence and severity of neglect. Eleven patients with right acute stroke and 11 healthy matched controls underwent MRI at 3T, including diffusion imaging, and T1-weighted volumes. TBSS was modified to account for the presence of the lesion and used to assess the presence and extension of changes in diffusion indices of microscopic white matter integrity in the left hemisphere of patients compared to controls, and to investigate, by correlation analysis, whether this damage might account for the presence and severity of patients'' neglect, as assessed by the Behavioural Inattention Test (BIT). None of the patients had any macroscopic abnormality in the left hemisphere; however, 3 cases were discarded due to image artefacts in the MRI data. Conversely, TBSS analysis revealed widespread changes in diffusion indices in most of their left hemisphere tracts, with a predominant involvement of the corpus callosum and its projections on the parietal white matter. A region of association between patients'' scores at BIT and brain FA values was found in the posterior part of the corpus callosum. This study strongly supports the hypothesis of a major role of structural disconnection between the right and left parietal cortex in determining ‘neglect’.     

The noradrenaline and serotonin content in symmetrical parts of the normal rat brain and during learning and peptide administration]

Content was compared of noradrenaline (NA) and serotonine (5-OT) in the right and left halves of the rats brain in norm, at elaboration of defensive conditioned reflexes of two-ways avoidance (CRTWA) and at administration of neuropeptides influencing the learning and memory--dezglycilargininvasopressin (DG-AVP), ACTH4-7 pro-gli-pro and dalargin. The conducted studies showed that in control animals the content of NA in the cortex of the right hemisphere was significantly higher than in the cortex of the left one. For the content of 5-OT in symmetric brain parts no significant differences were revealed. Under the elaboration of CRTWA the asymmetry of NA content was not eliminated. Systemic administration of DG-AVP, ACTG4-7 pro-gli-pro and dalargin practically did not change the content of 5-OT, but reduced the content of NA in the cortex and the rest of the brain, and the content of NA in the right and left cortex was equalized. The obtained data point to the asymmetric character of neuropeptides action and to greater resistance of 5-OT-ergic brain system to functional load and to administration of peptides in comparison with NA-ergic system.     

Activation of the parieto-premotor network is associated with vivid motor imagery--a parametric FMRI study

The present study examined the neural basis of vivid motor imagery with parametrical functional magnetic resonance imaging. 22 participants performed motor imagery (MI) of six different right-hand movements that differed in terms of pointing accuracy needs and object involvement, i.e., either none, two big or two small squares had to be pointed at in alternation either with or without an object grasped with the fingers. After each imagery trial, they rated the perceived vividness of motor imagery on a 7-point scale. Results showed that increased perceived imagery vividness was parametrically associated with increasing neural activation within the left putamen, the left premotor cortex (PMC), the posterior parietal cortex of the left hemisphere, the left primary motor cortex, the left somatosensory cortex, and the left cerebellum. Within the right hemisphere, activation was found within the right cerebellum, the right putamen, and the right PMC. It is concluded that the perceived vividness of MI is parametrically associated with neural activity within sensorimotor areas. The results corroborate the hypothesis that MI is an outcome of neural computations based on movement representations located within motor areas.     

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.     

Anatomical brain asymmetries in New World and Old World monkeys: stages of temporal lobe development in primate evolution

Relatively large (n = 20-30) samples of formalin-fixed brain specimens from five Old and New World monkey species were examined in a study measuring anatomical temporal-lobe asymmetries. Linear measurements of the length of the Sylvian fissure were taken on each cerebral hemisphere to evaluate lateral differences related to development of auditory association cortex. The results indicate significantly greater Sylvian fissure length on the left hemisphere than on the right hemisphere in four of these species. Measurements of a different parameter on Saimiri sciureus brain specimens (length of anterior portion of the Sylvian fissure) also suggested temporal-lobe asymmetry favoring the left hemisphere. Other measurements (length of the Sylvian fissure lying posterior to the central sulcus, and dorso-ventral position of the Sylvian point) in Macaca mulatta and M. fascicularis did not reveal significant right/left-hemisphere differences. Sylvian-fissure length determined from photographs of M. mulatta hemispheres in contrast to results of direct measurements did not yield significant right/left-hemisphere asymmetry. We mention possible reasons why previous anatomical studies of brains from monkeys did not discern temporal-lobe asymmetry, and we also discuss whether or not certain of these asymmetries in monkeys foreshadowed the evolution of language-processing areas of the cerebral cortex in hominids.     

Hemispheric asymmetry of the nigrostriatal system of the brain in rats genetically predisposed to catalepsy]

Hemispheric asymmetry of nigro-striate system in a strain of rats GC bred from Wistar for a predisposition to cataleptic reaction was studied by means of biochemical and morphological methods. Hemispheric asymmetry was found in GC and Wistar rats with respect to aminopeptidase activity in neurons of caudate nucleus, with a more pronounced left-side increase in GC rats, the asymmetry index being 13.7%. Acetylcholine esterase activity in subcellular particles of caudate nucleus showed an inversion of asymmetry with higher activity in the left hemisphere of Wistar and right hemisphere of GC rats, and asymmetry index of 15.5%. With respect to the number of astroglia cells in S. nigra, and astroglia and oligodendroglia in N. accumbens there was also an inversion of asymmetry in GC rats who had more cells in the structures of the left hemisphere, whereas Wistar rats had more in the right hemisphere. The asymmetry index was high and equal to 29.8% for astroglia in S. nigra, and 17% for astroglia and 21.4% for oligodendroglia in N. accumbens. However, in S. nigra the number of neurons and oligodendroglia cells was equally increased in the right hemisphere in GC and Wistar rats. The data suggest that the mechanism of hereditary pathology of brain nigro-striate system involves both enhancement and inversion of the hemispheric asymmetry.