Biomechanical properties of the human cranium: aging aspects

Biomechanical properties of the human skull affect its dynamic tensility (pliability, compliance) by changes of intracranial volume and pressure (deltaV/deltaP). The goal of this study is to substantiate a possibility of noninvasive and dynamic evaluation of cranial compliance. The transcranial dopplerogram of middle cerebral artery and hemispheric bioimpedance were synchronously recorded, which represent information about pulsative changes of intracranial pressure and volume, respectively. The parameters were recorded at rest and during adequate hemo- and liquorodynamic tests in different age groups--20-30, 40-50, and 70-85 years. As compared with the young group, a decrease of the cranial compliance in the intermediate age group was revealed due to an observed increase if rigidity of skull bones and ligaments, which indicates a decrease of stability of the intracranial circulatory system. However, in the group of 70-85 years the compliance rose again due to an enlargement of intracranial liquor spaces and facilitation of liquor circulation inside the intracranial cavity; this can be suggested to be a compensatory mechanism for supporting the adequate brain circulatory-metabolic state.     

Biomechanical properties of human cranium: Age-relayed aspects

Biomechanical properties of the human skull affect its dynamic tensility (pliability or compliance) at changes of intracranial volume and pressure (ΔV/ΔP). The work substantiates a possibility of noninvasive and dynamic evaluation of cranial compliance by synchronous recording of transcranial dopplerogram of middle cerebral artery and cranial bioimpedance that provides information about pulsative changes of intracranial pressure and volume, respectively, with subsequent computer pattern and phasic analysis of these processes. The characteristic peculiarities of the cranial compliance at rest and during action of functional hemo- and liquorodynamic tests were traced in people of the middle (40–50 years) and elderly (70–85 years) age groups as compared with the young group (20–30 years). A relative decrease of this parameter has been revealed in the middle age group due to an increase of rigidity of skull bones and ligaments, which indicates a decrease of tolerance of the intracranial circulatory system. However, in the group of 70–85 years the compliance parameters rose due to an increase of intracranial liquor volume and activation of liquor circulation inside the craniospinal space, which is a compensatory mechanism for maintenance of the adequate brain circulatory-metabolic activity.     

Asymmetry of modifications of the electrical activity of the rat cortex induced by intraventricular injections of thyrotropin-releasing hormone

We studied modifications in the mass electrical activity of the cortex (ECoG) induced by injections of thyrotropin-releasing hormone (TRH) into the left or right lateral brain ventricle in rats kept under conditions close to free behavior. It was found that these effects are characterized by a significant interhemisphere asymmetry. We postulate that the pharmacological (in particular, antidepressive) effects of TRH are related to its ability to intensify inhibitory processes in the left cerebral hemisphere and activating processes in the right hemisphere.Neirofiziologiya/Neurophysiology, Vol. 36, Nos. 5/6, pp. 386–390, September–December, 2004.This revised version was published online in April 2005 with a corrected cover date and copyright year.     

Asymmetry of the bioelectrical activity of the human brain at different levels of consciousness

Asymmetry of different human EEG indices was studied at different levels of consciousness. Subjects' self-reported changes in the content of consciousness: the intensity and quality of involuntary mental processes served as indicator of the level of consciousness. It was shown that a certain profile of EEG asymmetry corresponded to each the observed level of consciousness. In active state of consciousness, the connections in the high-frequency bands: beta-2 and gamma, were more pronounced in the left hemisphere of the brain. At the same time, transition of the focus of coherent connections to the right hemisphere was characteristic of the state of inhibition of "internal speech". The interhemisphere dynamics of autospectra amplitude and foci of coherent connections supports the notion that the character of interhemisphere asymmetry of the brain bioelectrical activity depends on its functional state.     

Specificity of Auditory Cognitive Evoked Potentials in Musicians

We measured characteristics of evoked potentials, EPs, developing after presentation of significant tonal acoustic stimuli in subjects systematically engaged in music training (n = 7) and those having no corresponding experience (n = 10). The peak latencies of the P3 component in the left hemisphere of musicians were significantly shorter than those in non-musicians (on average, 279.9 and 310.2 msec, respectively). Musicians demonstrated no interhemisphere differences of the latencies of components N2, P3, and N3, while a trend toward asymmetry was obvious in non-musicians (the above components were generated somewhat later in the left hemisphere). The amplitudes of EP components demonstrated no significant intergroup differences, but the amplitude of the P3 wave was higher in the left hemisphere of non-musicians than that in the right hemisphere. Possible neurophysiological correlates of the observed specificity of EPs in the examined groups are discussed.     

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.     

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.     

Vervet monkeys and humans show brain asymmetries for processing conspecific vocalizations, but with opposite patterns of laterality

A robust finding in the human neurosciences is the observation of a left hemisphere specialization for processing spoken language. Previous studies suggest that this auditory specialization and brain asymmetry derive from a primate ancestor. Most of these studies focus on the genus Macaca and all demonstrate a left hemisphere bias. Due to the narrow taxonomic scope, however, we lack a sense of the distribution of this asymmetry among primates. Further, although the left hemisphere bias appears mediated by conspecific calls, other possibilities exist including familiarity, emotional relevance and more general acoustic properties of the signal. To broaden the taxonomic scope and test the specificity of the apparent hemisphere bias, we conducted an experiment on vervets (Cercopithecus aethiops)-a different genus of old world monkeys and implemented the relevant acoustic controls. Using the same head orienting procedure tested with macaques, results show a strong left ear/right hemisphere bias for conspecific vocalizations (both familiar and unfamiliar), but no asymmetry for other primate vocalizations or non-biological sounds. These results suggest that although auditory asymmetries for processing species-specific vocalizations are a common feature of the primate brain, the direction of this asymmetry may be relatively plastic. This finding raises significant questions for how ontogenetic and evolutionary forces have impacted on primate brain evolution.     

Interhemisphere Asymmetry of the Pro-/Antioxidant Systems in the Rat Brain: Effects of Hypokinesia and Extrahigh-Frequency Electromagnetic Radiation

We studied changes in the interhemisphere asymmetry of the intensity of lipid peroxidation (LPO) and total content of thiol groups (TTG) in the rat cerebral neocortex. These indices characteristic for animals with different motor phenotypes (dextrals, sinistrals, and ambidextrals) were measured in the control and under the influence of hypokinesia, low-intensity millimeter-range electromagnetic radiation (mmR EMR), and their combination. The development of hypokinetic stress in rats (after 10-day-long motor restriction) resulted in a sharp activation of LPO and suppression of thiol/disulfide metabolism in the neocortex of rats with different types of motor asymmetry. Hypokinesia was accompanied by considerable drops in the coefficients of interhemisphere asymmetry (up to reversal of their signs); this can be related to decreases in the resistivity of the organism to stress and adaptability to external influences. When intact animals with different types of motor asymmetry were irradiated with mmR EMR, the intensity of LPO in the neocortex of both hemispheres decreased concurrently with intensification of thiol/ disulfide metabolism. The combined influence of hypokinesia and mmR EMR led to considerably smaller shifts in the above indices, as compared with those after isolated action of hypokinesia. When mmR EMR influenced animals were kept under conditions of normal motor mode and motor restriction, the signs of the coefficients of asymmetry of the indices under study did not change, while the intensity of interhemisphere asymmetry increased. We suppose that this is related to an increase in the adaptability of the organism to the action of stressor factors.     

Asymmetry of the transcallosal responses in the parietal cortex of kittens in the 1st month of life

In acute experiments on kittens the process of formation of asymmetry of transcallosal responses (TCR) was studied in multiple leads from symmetrical points of the parietal cortex. By the early positive-negative TCR complex, vanishing as a result of callosotomy, predominance of positive components in the right hemisphere was found in 2-7 days kittens, whereas in 8-24 days animals the left hemisphere dominated by both phases of responses. By the late TCR component preserved after section of the callosal body, left-hemispheric asymmetry was found in the elder group of kittens; it was absent in the younger animals. TCR asymmetry in the parietal cortex depended on the sex of the animals. With their age its inversion and enhancement took place. This process is based on the increase of TCR amplitude in the left hemisphere, with no increase in the right hemisphere.     

Interhemisphere asymmetry of hippocampus and neocortex in correlates of active and passive behavioural strategy in negative emotional situations

The interhemisphere interaction of neurons in bilateral derivations from parietal and sensomotor areas of neocortex and the area CA1 of hippocampus were studied in rabbits with active and passive behavioural strategy in the open field by plotting histograms of crosscorrelation. In passive animals, there was asymmetry in bilateral neuronal interaction: with right-sided dominance in the neocortex and with left-sided that--in the hippocampus. On the contrary, in active rabbits, the left-sided dominance was observed in the neocortex, and the lateralization was not revealed in the hippocampus. The brain laterality was reflected in motor asymmetry of animals in preferring left or right turns in the open field. Passive rabbits made relatively more left turns, and the active animals--right turns. Systemic administration of agonist GABA(B) receptors phenibut decreased behavioural responses to emotional stimuli and eliminated interhemisphere asymmetry observed usually in negative emotional situations. Thus the interhemisphere asymmetry of the neocortex and hippocampus is correlated with individual typological characteristics of animals and reflects the readiness to preferential forms of behavioural responses in active and passive rabbits.     

Hemispheric asymmetries in cortical electrical activity during sleep. I

The hypothesis of a predominance of the right hemisphere in stage REM as compared to NREM has been tested through a spectral analysis of the EEG recorded from left (T3) and right (T4) temporal sites in 5 young healthy right-handed male subjects. Variations in the asymmetry coefficient R - L/R + L in different sleep stages have been analyzed by one way ANOVAs and Sheffé's tests. The hypothesis of a progressive increase in left hemisphere activity throughout different REM cycles as one approaches final awakenings have been investigated by comparing variations in the asymmetry coefficient for epochs of REM and stage 2 NREM sampled in different phases of the REM cycle. EEG results do not support either the hypothesized stage dependent or cycle dependent variation in EEG activity during sleep. We question whether variations in EEG amplitude and synchronization can be used as indices of hemispheric asymmetries during sleep.     

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.     

Interhemispheric asymmetry of positive emotional reactions in rats

Interhemispheric asymmetry of positive emotional reactions was studied in rats: satisfaction of drinking need and self-stimulation. Successive inactivation of the hemispheres was carried out by potassium spreading depression. Switching off of the right as well as the left hemispheres symmetrically influenced the whole quantity of the water, drunk by the rats to a full thirst satisfaction, i. e. the magnitude of need. However, at different stages of drinking need satisfaction an interhemispheric asymmetry was observed: under a strong drinking motivation the right hemisphere dominated, under a weak motivation--the left one. Switching off of the right hemisphere lowered the frequency of self-stimulation of the lateral hypothalamus and switching off the left one heightened it, testifying to the dominance of the right hemisphere in the reaction of self-stimulation. This reaction was also characterized by asymmetry of the lateral hypothalamus nuclei; reactivity to hemispheres inactivation (decreasing or increasing of self-stimulation frequency) of the right nucleus was more expressed than that of the left one.     

The effect of sex steroid hormones on interhemispheric asymmetry in rats]

The effect of gonadectomy and sex-steroid hormones treatment on functional interhemispheric asymmetry to the reaction of pain cry avoidance of another species (emotional reactions) and motor and exploratory activity of open-field behavior in Wistar rats of 3 months old has been investigated. A spreading depression technique for hemisphere inactivation has been used. The hemispheric asymmetry of the reactions in intact rats was characterized by sex dimorphism; the left hemisphere dominated to a great extent in males than in females under the control of emotional reactions; in motor and exploratory activity in open-field behavior of rats the left hemisphere dominated in males and the right one--in female. In both sexes the neonatal gonadectomy levelled the interhemispheric differences in reactions under investigation. The following treatment of females with estradiol and males with testosterone didn't restore the asymmetry. After the castration at the age of 3 months the correlation between the size and direction of interhemispheric differences became reverse. The treatment of females with testosterone and males with estradiol both castrated in adulthood restored the interhemispheric asymmetry in males and had no effect in females. The treatment of intact rats with hormones of opposite sex led to the enhancement of left hemisphere dominance in motor and exploratory activity in males and levelled the asymmetry in females. It has been shown that in adult rats sex-steroids effect predominantly the right hemisphere.     

Changes in the spectral power and coherence of the EEG alpha rhythm in humans performing grasp efforts by the right and left arm

We compared changes in the EEG indices in healthy dextral volunteers performing static force grasps by the arm. Three test modes were used: (i) performance of two successive grasps by the dominant (right) arm (test A), (ii) performance of two successive grasps by the subdominant (left) arm (test B), and (iii) performance of the grasps first by the right arm and then by the left arm (test C). Fourteen, six, and nine persons took part in tests A–C, respectively. In the course of grasps performed by the right and left arms, bilateral increases in synchronization within the alpha 1 and alpha 2 ranges were frequently observed in occipital regions in both the first and repeated grasps (P < 0.05). Consecutive grasps by the right arm were accompanied by clear desynchronization in a few anterior and central leads. Alpha 2 desynchronization was observed in both realizations of the left-arm grasps (test B) performed by some subjects, but intragroup modifications were not significant in this case. The coherence coefficients of the alpha 2 rhythm in most cases increased for symmetric leads from the right and left hemispheres in the course of grasps by both the right and left hands. The effect of intensification of interhemisphere links was manifested in the anterior and central cortical regions; this fact showed that interhemisphere interaction increases in the course of the static effort. Changes in the coherence coefficients for the alpha 2 range in the performance of the grasp efforts by the right arm and the left arm were most clear in the posterotemporal (P = 0.02), parietal (P = 0.05), and anterofrontal (P = 0.06) lead pairs. Thus, we demonstrated the dependence between the side of performance of the muscle effort in the mode close to isometric and lateralization of the EEG modifications. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 235–238, May–June, 2006.     

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.     

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.     

Physical criteria of pathological processes. I. Change in the functional hemispheric asymmetry at various stages of rheumatic diseases]

The functional interhemispheric asymmetry of brain in patients with systemic rheumatic diseases was estimated by measuring brain direct current potentials. It is shown that different types of functional interhemispheric asymmetry correspond to different stages of systemic rheumatic diseases. At early stages, the left hemisphere asymmetry dominates, at expressed stages, the right hemisphere asymmetry is prevalent, and the terminal stage is characterized by the loss of functional interhemispheric asymmetry.     

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.