Differences in vulnerability between the hemispheres in early childhood and adulthood

There are more left hemisphere damaged than right hemisphere damaged children and adults if one relies on studies of congenital hemiparesis as well as on those done on groups with radiologically demonstrated perinatal and postnatal unilateral stroke, hemispherectomy, or unilateral epilepsy in childhood or adulthood. The main pathogenetic factor seems to be a hemodynamic one, responsible for insufficient blood supply to the left hemisphere. Since adults show a difference in the same direction as children, the blood supply to the left internal carotid artery would seem to be the crucial factor. Around birth, an open ductus arteriosus may play an additional role. The hemodynamic asymmetry does not exclude an intrinsic maturational hemispheric tissue factor, making the left hemisphere more vulnerable than the right to detrimental influences around birth and during the early postnatal period. Immature white matter is especially vulnerable to asphyxia. The text was submitted by the author in English.     

Higher density of mental capacities in the left cerebral hemisphere of man: a quantitative investigation in children with localized cerebral lesions

51 children with localized cerebral lesions were investigated with the British Ability Scales, Wechsler test, Porteus Mazes, Conners Teacher Rating Scale, and computerized tomography. The extent of the lesions was quantitatively determined. The IQ was 10 points lower in the left hemispheric lesions, although the right hemispheric lesions were larger. When corrected for size of lesions, the IQ is 17 points higher (p less than 0.05) in children with right than with left hemispheric early lesions. The children with left hemispheric lesions had also significantly more behavioural problems (Conners Scale). Children with bilateral lesions had 15 points lower IQ than those with unilateral lesions, although from the slightly larger extent one could expect only 3 points difference. There was no influence of hemiparesis or of epilepsy of the IQ independent of the extent of lesion. There was more plasticity of the hemisphere than of the lobes as shown by Wisconsin Card Sorting data. The higher density of mental capacities in the left cerebral hemisphere of man is explained by more efficient programs, and more dense packing of functions due to more training of the left cerebral hemisphere.     

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.     

Hemodynamic component in cerebral compensatory processes following unilateral exclusion of the somatosensory cortex]

In experiments on anesthetised and awake cats the dynamics of the cerebral blood flow was studied by the thermoelectric method in one hemisphere in experimental lesion of the somatosensory zone of the opposite one. Temporary exclusion of the cortical area by cold produced evident hemodynamic changes, i. e. a two-phase vasoreaction and an initial blood flow decrease followed by a prolonged increase of blood supply, in the other hemisphere. Analogous vasoreactions were seen on unilateral extirpation of the cortical layer of the somatosensory zone, as well. Such vasoreactions indicate enhanced activity of the cortical structures in the intact hemisphere and may be considered as a compensatory reaction to the local lesion of certain cortical areas.     

Sex Differences and Activity of the Left and Right Brain Hemispheres

The problem is reviewed of sex differences and the brain organization of the visual-spatial and verbal-cognitive functions both in adults and in the 5–15-year old children. Characteristic of men are the integral strategy of the face image recognition, specialization of the right hemisphere for visual-spatial functions, and the tonic inhibitory effect of the right hemisphere on the left one. Typical of women are the fragmented type of the image recognition, the equality of the brain hemispheres functions at the unfamiliar face recognition, and predominance of the left hemisphere by accuracy of the object localization in the visual field. It is possible that the general strategy of the recognition in women is not realized due to the right hemisphere submitted to the interfering effect of the left hemisphere. Analysis of sex differences in distribution of verbal functions shows that the capability for the verbal learning at the age of 5 years and older is higher in girls than in boys. Such capability seems to be accounted for by the superiority of the left hemisphere in girls in this type of its activity and by its earlier development and maturation. The phenomenon of semantic paralexia appearing more often in boys is accounted for by inclusion of lexical-semantic fields of the right hemisphere symmetric areas in the verbal-cognitive activity There are reasons to believe that the higher capability in girls for the verbal learning is mainly due to processes of the auditory-verbal integration within the limits of the left hemisphere, whereas this verbal ability in boys depends on the relative predominance of the interhemispheric connections.     

Hemispheric dominance of cortical activity evoked by focal electrogustatory stimuli.

Functional magnetic resonance imaging was used to observe cortical hemodynamic responses to electric taste stimuli applied separately to the right and left sides of the tongue tip. In 11 right-handed normal adults activation occurred primarily in the insular cortex, superior temporal lobe, inferior frontal lobe, including premotor regions, and in inferior parts of the postcentral gyrus. Unexpectedly, the location and laterality of activation were largely identical regardless of the side of the tongue stimulated. Activation in the superior insula, the presumed location of primary gustatory cortex, was predominantly, but not exclusively, in the right hemisphere, whereas central (more inferior) insular activations were more evenly bilateral. Right hemispheric dominance of activation also occurred in premotor regions (Brodmann areas 6 and 44), whereas left hemispheric dominance occurred only in the superior temporal cortex (Brodmann areas 22/42). The electric taste-evoked hemodynamic response pattern was more consistent with activation of the gustatory system than activation of somatosensory systems. The results suggest that the sites for cortical processing of electric taste information are dependent on hemispheric specialization.     

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.     

Compensatory recovery of vagal control of hemodynamics after unilateral vagotomy

This study investigated whether each part of the heart is evenly innervated by the left or right vagus and observed the mechanism of compensatory recovery after unilateral cervical vagotomy. HR, BP, LVSP and +/-dp/dt max all decreased one week after left vagotomy, whereas only BP and -dp/dt max decreased one week after right vagotomy. Western blot analyses revealed that the expression of M(2) receptors in the left atrium and left ventricle was upregulated after subacute (1 week) left/right vagotomy. However, significantly more cholinesterase-positive nerves in LV and RV were seen one week after unilateral vagotomy compared to the sham-operated group. In addition, baroreflex sensitivity was increased after subacute right vagotomy. The decreasing effects of ACh (0.5 microg/kg) on LVSP and +/-dp/dt max (but not on HR and BP) were facilitated by subacute unilateral vagotomy. Our present experiments indicate that 1) the working myocardium is innervated bilaterally by the vagus, 2) ventricular contractility is influenced more by denervation of the left than the right vagus and 3) up-regulation of M(2) muscarinic receptors in the left heart, increase of cholinergic nerves, and high baroreflex sensitivity could be involved in the mechanism of compensatory hemodynamic recovery via contralateral vagus overactivity, thereby amplifying contralateral vagal activity and decreasing cardiac contractility.     

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.     

去胡须对大鼠行为及桶状皮层的影响

目的:研究外周去胡须后大鼠行为及桶状皮层(barrel cortex,BC)的可塑性变化。方法:SD大鼠随机分组(n=4):正常对照(A组),出生后第2天去除双侧颊脂垫组(B组),出生后第2天去除右侧颊脂垫组(C组),出生后1～5d每天剪右侧胡须,从出生后第5天起不剪由其胡须自由生长组(D组)。出生后第30天时称体重,测量左侧D2胡须长度,观测行为学变化(如狭缝实验、自由探索行为和趋壁行为)。采用细胞色素氧化酶组织化学法研究barrel排列与发育情况。结果:A组能迅速辨别出正确狭缝并钻入,平均用时(5.6±2.3)s;B组大鼠只有当鼻尖碰到狭缝壁时才会钻入狭缝。C组大鼠当其右侧脸颊靠近狭缝时,不能辨别出狭缝,只有当其掉转身体,用左侧胡须探测时才可能迅速钻入正确的狭缝。D组的表现同C组,B、C、D组大鼠进入正确狭缝的所用时间均显著长于A组(P0.01,P0.05,P0.01)。去除双侧颊脂垫的大鼠其左趋壁时间、右趋壁时间以及总趋壁时间均较正常大鼠短。去除右侧颊脂垫组的大鼠右趋壁时间也显著短于正常(P0.05)。四组大鼠左侧D2胡须长度以及体重均无显著差异。从出生后第2天时一直剪除右侧胡须的小鼠在出生后第30天时发现其barrel变小,排列较混乱,barrel之间的界限不清,皮层细胞色素氧化酶(CO)反应的灰度明显变淡。结论:外周去传入不引起大鼠体重改变及残留胡须长度的代偿性改变,但可引起其趋触及探索行为方面的改变。外周去传入可导致barrel形状及排列的可塑性变化。     

Laterality of the olfactory event-related potential response

In experimental practice, odors are commonly applied to only one nostril for recordings of olfactory event-related potentials (OERPs), but the lateralization aspect of the OERP response is unclear regarding both stimulated nostril and cortical topography. The purpose of the present study was to investigate whether stimulated-nostril side affects OERP amplitudes and latencies and whether these potentials indicate lateralization of brain response in healthy, right-handed, young adults. OERPs were recorded from nine electrode sites in response to monorhinal stimulation with amyl acetate in 28 participants. The results showed a general increase in amplitude from frontal to parietal electrode sites (in particular for N1/P3) and generally larger amplitudes on the left hemisphere and midline than on the right hemisphere. There was no main effect of stimulated-nostril side on amplitude. Interactions indicated that N1/P2 amplitude was larger for left- than right-nostril stimulation and larger on the left hemisphere and midline than on the right hemisphere in left-nostril stimulation. No main effect or interactions of stimulated-nostril side over latencies were found and no effects on latencies of sagittal or coronal sites. These findings suggest a general parietal, left-hemisphere predominance in response amplitude to odorous stimulation and imply that either the left or the right nostril may be sufficient for accurate assessment of OERP latency in right-handed, young adults.     

Evidence for developmental programming of cerebral laterality in humans

Adverse fetal environments are associated with depression, reduced cognitive ability and increased stress responsiveness in later life, but underlying mechanisms are unknown. Environmental pressures on the fetus, resulting from variations in placental function and maternal nutrition, health and stress might alter neurodevelopment, promoting the development of some brain regions over others. As asymmetry of cerebral activity, with greater right hemisphere activity, has been associated with psychopathology, we hypothesized that regional specialization during fetal life might be reflected persistently in the relative activity of the cerebral hemispheres. We tested this hypothesis in 140 healthy 8–9 year-old children, using tympanic membrane temperature to assess relative blood flow to the cerebral hemispheres at rest and following psychosocial stress (Trier Social Stress Test for Children). Their birth weight and placental weight had already been measured when their mothers took part in a previous study of pregnancy outcomes. We found that children who had a smaller weight at birth had evidence of greater blood flow to the right hemisphere than to the left hemisphere (r = −.09, P = .29 at rest; r = −.18, P = .04 following stress). This finding was strengthened if the children had a relatively low birth weight for their placental weight (r = −.17, P = .05 at rest; r = −.31, P = .0005 following stress). Our findings suggest that lateralization of cerebral activity is influenced persistently by early developmental experiences, with possible consequences for long-term neurocognitive function.     

Systemic Organization of Perceptive Activity in Children with Different Levels of Mental Development

Visual evoked potentials (EPs) of the left and right hemispheres in response to relevant and irrelevant stimuli in the structures of the left and right hemispheres have been studied in healthy young schoolchildren, learning-disabled (LD) children, and mentally retarded (MR) children. In healthy children, the largest EP variations depending on the stimulus relevancy have been found in associative structures of the left hemisphere. In LD children of the same age, the amplitude and temporal characteristics of left-hemispheric EPs to target and nontarget stimuli are the same. In MR children, EPs to relevant and irrelevant stimuli do not differ from each other in either the left or the right hemisphere. EP latencies are significantly longer in MR children than in healthy children. The results of simultaneous recording of EPs in the left and right hemispheres during isolated stimulation of the right and left visual half-fields indicate that interhemispheric interaction is impaired in children with deviations in mental development. The results of the study are discussed in terms of the psychological characteristics and learning ability of children.     

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.     

Functional organization of the brain in the period of preparation for recognizing fragmented images in seven- to eight-year-old children and adults

Functional connectivity between the prefrontal cortex and the temporal and temporo-parieto-occipital cortices in the process of preparing for the recognition of fragmented images were analyzed in adults (n = 26) and seven- to eight-year-old children (n = 20).The evaluations of the imaginary part of the complex-valued coherency for the EEG alpha-rhythm (Jα) were used as an index for the strength of cortico-cortical interactions. The Jα value was analyzed in the following three experimental conditions corresponding to different stages of readiness for visual recognition: (1) nonspecific attention holding in the period preceding a warning stimulus (S1); (2) focused attention in the interval preceding a not-yet-recognized target stimulus (S2) and (3) pretuning preceding a recognized stimulus (S3). Adult subjects tended towards a growing level of functional connectivity in α-rhythm in progressing from attention holding to focused attention preceding the emergence of a target stimulus, but children, on the contrary, demonstrated a decreasing trend. Comparing the Jα values in the subgroups of adults and children who showed the highest recognition scores in the solution of cognitive tasks helped reveal age-specific patterns in the rearrangements of cortico-cortical functional connectivity in α-rhythm in the left and right hemispheres at different stages of readiness for recognizing incomplete images. In adults, the maximal Jα values were found in the left hemisphere in the interval preceding the recognition of a target image. At this stage of pretuning, the Jα values at the leads in the left hemisphere in adults significantly exceeded those in children. The Jα values for the right hemisphere in adults were maximal during focused prestimulus attention when the image was not yet recognized and these values were significantly higher than in children under the same experimental conditions. Children showed maximal Jα values in both hemispheres during nonspecific attention. The specifics of functional connectivity observed between the prefrontal, temporal and temporo-parieto-occipital cortices in seven- to eight-year-old children during functional pretuning to the recognition of fragmented images are considered to reflect the relative immaturity of neurophysiological mechanisms underlying the voluntary attention and working memory in children of this age group.     

Interhemispheric EEG asymmetries during unilateral bright-light exposure and subsequent sleep in humans

We tested whether evening exposure to unilateral photic stimulation has repercussions on interhemispheric EEG asymmetries during wakefulness and later sleep. Because light exerts an alerting response in humans, which correlates with a decrease in waking EEG theta/alpha-activity and a reduction in sleep EEG delta activity, we hypothesized that EEG activity in these frequency bands show interhemispheric asymmetries after unilateral bright light (1,500 lux) exposure. A 2-h hemi-field light exposure acutely suppressed occipital EEG alpha activity in the ipsilateral hemisphere activated by light. Subjects felt more alert during bright light than dim light, an effect that was significantly more pronounced during activation of the right than the left visual cortex. During subsequent sleep, occipital EEG activity in the delta and theta range was significantly reduced after activation of the right visual cortex but not after stimulation of the left visual cortex. Furthermore, hemivisual field light exposure was able to shift the left predominance in occipital spindle EEG activity toward the stimulated hemisphere. Time course analysis revealed that this spindle shift remained significant during the first two sleep cycles. Our results reflect rather a hemispheric asymmetry in the alerting action of light than a use-dependent recovery function of sleep in response to the visual stimulation during prior waking. However, the observed shift in the spindle hemispheric dominance in the occipital cortex may still represent subtle local use-dependent recovery functions during sleep in a frequency range different from the delta range.     

巨大右半肝肿瘤切除术时的出血控制

巨大右半肝肿瘤切除过程中的出血量是决定手术能否成功的关键因素,控制手术过程中出血的技术也是右半肝切除术中的最重要的技术,有效控制术中出血的方法贯穿于整个手术过程中：良好的术前评估,术中于第一肝门处选择性阻断支配右半肝的入肝血流,于第二肝门处切断肝右静脉,于第三肝门处切断肝短静脉,在无血条件下用超声吸引刀切除预定的右半肝以及肝断面的处理等。此方法能有效控制手术过程中出血,保证左半肝血液供应,减轻肝脏缺血/再灌注损伤,减少术后肝功能不全的发生,保证了胃肠道血流的通畅,避免了黏膜屏障受损,全身血流动力学平稳,对其他脏器功能影响小,缩短了手术时间,极大地提高了手术的安全性。     

Getting a Grip on Memory: Unilateral Hand Clenching Alters Episodic Recall

Unilateral hand clenching increases neuronal activity in the frontal lobe of the contralateral hemisphere. Such hand clenching is also associated with increased experiencing of a given hemisphere’s “mode of processing.” Together, these findings suggest that unilateral hand clenching can be used to test hypotheses concerning the specializations of the cerebral hemispheres during memory encoding and retrieval. We investigated this possibility by testing effects of unilateral hand clenching on episodic memory. The hemispheric Encoding/Retrieval Asymmetry (HERA) model proposes left prefrontal regions are associated with encoding, and right prefrontal regions with retrieval, of episodic memories. It was hypothesized that right hand clenching (left hemisphere activation) pre-encoding, and left hand clenching (right hemisphere activation) pre-recall, would result in superior memory. Results supported the HERA model. Also supported was that simple unilateral hand clenching can be used as a means by which the functional specializations of the cerebral hemispheres can be investigated in intact humans.     

Interhemispheric differences in the spectral power and coherence of EEG rhythms in children with autism spectrum disorders

Electroencephalographic examination of boys aged 4–9 years with autism spectrum disorders (ASDs) showed spectral power values and coherence in high-frequency bands (20–60 Hz) in various brain areas were higher than normal. Differences in spectral power were greater in the anterior areas of the left hemisphere; differences in coherence, in the right anterior and posterior areas. Interhemispheric differences typical of healthy subjects were absent in the children with ASDs. The spectral power of the θ rhythm was lower in autism, especially in the left hemisphere. The spectral power of the α rhythm in the autistic children was lower than normal, especially in the posterior areas of the left hemisphere. The μ rhythm was higher than normal in spectral power and was localized in the right, rather than left, anterior areas. The children were examined again after corrective procedures. The α-rhythm spectral power increased (became closer to the norm) in the left posterior areas, while the γ-rhythm spectral power decreased (became closer to the norm) in the right anterior areas in some of the autistic children. The electrophysiological changes were associated with improved psychological testing results, especially in nonverbal measures.     

Spatial attention and neglect: parietal, frontal and cingulate contributions to the mental representation and attentional targeting of salient extrapersonal events.

The syndrome of contralesional neglect reflects a lateralized disruption of spatial attention. In the human, the left hemisphere shifts attention predominantly in the contralateral hemispace and in a contraversive direction whereas the right hemisphere distributes attention more evenly, in both hemispaces and both directions. As a consequence of this asymmetry, severe contralesional neglect occurs almost exclusively after right hemisphere lesions. Patients with left neglect experience a loss of salience in the mental representation and conscious perception of the left side and display a reluctance to direct orientating and exploratory behaviours to the left. Neglect is distributed according to egocentric, allocentric, world-centred, and object-centred frames of reference. Neglected events can continue to exert an implicit influence on behaviour, indicating that the attentional filtering occurs at the level of an internalized representation rather than at the level of peripheral sensory input. The unilateral neglect syndrome is caused by a dysfunction of a large-scale neurocognitive network, the cortical epicentres of which are located in posterior parietal cortex, the frontal eye fields, and the cingulate gyrus. This network coordinates all aspects of spatial attention, regardless of the modality of input or output. It helps to compile a mental representation of extrapersonal events in terms of their motivational salience, and to generate 'kinetic strategies' so that the attentional focus can shift from one target to another.