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.     

Auditory agnosia

Auditory agnosia can be defined as the defective recognition of non-verbal sounds and noises. The clinical picture of this disorder is described and the scarcity of knowledge of auditory agnosia derived purely from single cases is discussed. Next, experimental studies on unselected series of brain-damaged patients, especially designed to clarify the relation of auditory agnosia to aphasia and to the hemispheric locus of the lesion are reported. The results consistently point to the existence of two types of auditory agnosia, a semantic-associative one, specifically associated with lesions of the left hemisphere and aphasia, and a discriminative one, specifically associated with lesions of the right hemisphere. The hypothesis is advanced that the semantic-associative variety of auditory agnosia is part of a wider cognitive disorder.     

Word retrieval learning modulates right frontal cortex in patients with left frontal damage

Previous studies have suggested that recovery or compensation of language function after a lesion in the left hemisphere may depend on mechanisms in the right hemisphere. However, a direct relationship between performance and right hemisphere activity has not been established. Here, we show that patients with left frontal lesions and partially recovered aphasia learn, at a normal rate, a novel word retrieval task that requires the damaged cortex. Verbal learning is accompanied by specific response decrements in right frontal and right occipital cortex, strongly supporting the compensatory role of the right hemisphere. Furthermore, responses in left occipital cortex are abnormal and not modulated by practice. These findings indicate that frontal cortex is a source of top-down signals during learning.     

Language-related hemispheric asymmetry in healthy subjects and patients with temporal lobe epilepsy as studied by event-related brain potentials and intracarotid amobarbital test

There are current attempts to replace the WADA test for pre-surgical evaluation of hemispheric language capabilities by one of the methods of functional brain imaging. Recent PET and fMRI studies using verbal cognitive tasks like verb generation, semantic monitoring or semantic (`deep') encoding of words showed asymmetries of activation in the fronto-lateral cortex. In a previous ERP study subjects were required to indicate whether pronounceable non-words and abstract geometric figures were presented for the first time (`new item') or whether they had been shown before (`old item'). Group analyses of this study showed significant material-specific hemispheric asymmetries with ERPs being more negative-going in recordings of the posterior part of the left hemisphere with verbal material (CP5/6) but more negative-going in recordings of the right hemisphere with the spatial material (P7/8). The aim of the present study was to test statistically ERP lateralization effects in individual healthy subjects as well as WADA-tested patients suffering from seizures of the mesio-temporal lobe (MTL). In all subjects ERP lateralization with verbal material was tested in the electrode pair CP5/6, and ERP lateralization with figures in the electrode pair P7/8. Statistical analyses of single trials showed that in 20 out of 24 subjects ERPs with verbal material started to be more negative-going in CP5 as compared to CP6 in the period between 100 and 200 ms after stimulus onset or the subsequent time epoch (200–300 ms). In one subject not CP5/6 but the closely adjacent electrode pair P7/P8 showed this verbal material-related hemispheric effect. In patients language dominance as indicated by ERPs was not always consistent with the data of the WADA test. In one patient with left MTL seizures ERPs with verbal material and figures were found to be significantly lateralized to the right hemisphere although the WADA test assigned this patient to have a language-dominant left hemisphere.     

Age- and Sex-Dependent Laterality of Rat Hippocampal Cholinergic System in Relation to Animal Models of Neurodevelopmental and Neurodegenerative Disorders

Studies suggest age- and sex-dependent structural and functional patterns of human cerebral lateralization underlie hemisphere specialization and its alterations in schizophrenia. Recent works report sexual dimorphism of neurons in the hippocampal formation and specialization of hemispheres in rats. Our experiments indicate for the first time functional lateralization of the high-affinity choline uptake (HACU) system directly associated with a synthesis of acetylcholine in the hippocampus of Wistar rats. The markedly increased HACU activity was found in the left compared to the right hippocampus of adult male but not female animals. Lineweaver-Burk plot analysis revealed a statistically significant increase of Vmax in the left hippocampus of 14-day-old when compared to 7-day-old males. It appears that laterality of HACU occurs during late postnatal maturation, and its degree is markedly enhanced after puberty and attenuated during aging. Quinolinic acid (QUIN), an endogenous agonist of N-methyl-D-aspartate type glutamate receptors, was used in this study to evaluate the neurodevelopmental hypothesis of schizophrenia. It is known that elevated levels of QUIN accompany viral infections, increasing the risk of developing schizophrenia. Bilateral intracerebroventricular application of QUIN (250 nmoles/ventricle) to pups aged 12 days significantly impaired the cholinergic hippocampal system of adolescent male and female rats and reversed lateralization of male HACU. Morphological analysis indicated marked changes in brain lesion sizes (extensive 24 h and moderate 38 days after the operation). Asymmetry of lesions was observed in the majority of cases, but the left hemisphere was not generally more vulnerable to QUIN effects than the right side. Moreover, no lateral differences were found between lesioned hippocampi in the specific binding of [3H]hemicholinium-3 (10%-15% loss of binding sites when compared to sham-operated animals). In summary, our results indicate a symmetrical drop in the number of choline carriers of lesioned male rats but a asymmetrical decrease in the activity of remaing carriers, suggesting defects in processes of sexual brain differentiation, leading under normal conditions to the higher activity of carriers in the left hippocampus. The data demonstrate viral infection-mediated alterations in normal patterns of brain asymmetry and are discussed in relation to animal models of neurodevelopmental and neurodegenerative diseases.     

Does emotional state influence motor lateralization in California sea lions (<Emphasis Type="Italic">Zalophus californianus</Emphasis>)?

Motor lateralization is a behavioural asymmetry between the left and the right side of an individual due to hemispheric specialization. The right hemisphere controls the left side of the body and the left hemisphere the right side. The right hemisphere processes negative emotions such as fear and frustration, and on the contrary, the left hemisphere processes positive emotions such as happiness. This study, conducted at Parc Asterix Delphinarium (Plailly, France), tested the influence of supposedly positive, negative and neutral emotional situations on four California sea lions’ (Zalophus californianus) motor lateralization while performing a known exercise, here climbing on a stool. Latency between the caretakers’ command and the animals’ response was recorded. The results showed an interindividual variability in the effect of the supposed emotional situations on their motor lateralization and their response latency. The nature and the strength of this effect require deeper investigation by further studies, on a larger number of individuals and contexts.     

Cerebral Asymmetry of fMRI-BOLD Responses to Visual Stimulation

Hemispheric asymmetry of a wide range of functions is a hallmark of the human brain. The visual system has traditionally been thought of as symmetrically distributed in the brain, but a growing body of evidence has challenged this view. Some highly specific visual tasks have been shown to depend on hemispheric specialization. However, the possible lateralization of cerebral responses to a simple checkerboard visual stimulation has not been a focus of previous studies. To investigate this, we performed two sessions of blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) in 54 healthy subjects during stimulation with a black and white checkerboard visual stimulus. While carefully excluding possible non-physiological causes of left-to-right bias, we compared the activation of the left and the right cerebral hemispheres and related this to grey matter volume, handedness, age, gender, ocular dominance, interocular difference in visual acuity, as well as line-bisection performance. We found a general lateralization of cerebral activation towards the right hemisphere of early visual cortical areas and areas of higher-level visual processing, involved in visuospatial attention, especially in top-down (i.e., goal-oriented) attentional processing. This right hemisphere lateralization was partly, but not completely, explained by an increased grey matter volume in the right hemisphere of the early visual areas. Difference in activation of the superior parietal lobule was correlated with subject age, suggesting a shift towards the left hemisphere with increasing age. Our findings suggest a right-hemispheric dominance of these areas, which could lend support to the generally observed leftward visual attentional bias and to the left hemifield advantage for some visual perception tasks.     

Association Process and Functional Brain Asymmetry

Analysis is presented of word associations produced by subjects with left hemispheric (group 1), right hemispheric (group 2), and bilateral (group 3) speech representation. The strategy for producing extralinguistic responses was found to prevail over the strategy for producing linguistic associations in all subjects, irrespective of their type of speech representation. This strategy was more pronounced in subjects with right hemispheric speech laterality, suggesting a correlation between the generation of extralinguistic associations and functional brain asymmetry. Producing linguistic associations also depended on the type of cerebral organization of speech. The most important linguistic associations are syntagmatic. Syntagmatic associations were more closely related to the lateralization of speech to the left hemisphere. The data are compared to the results of studies of the ontogeny of associative processes.     

Vascular lesions of the thalamus on the dominant and nondominant side.

A clinicopathological study was done on 87 subjects with VPL lesions due to vascular pathology, with special reference to the difference of clinical manifestations between the right and left sides. Thalamic pain was far more common in VPL lesions on the right side. The responsible lesions for thalamic pain were observed in lesions of VPL and VPL extending to the internal capsule, while in the lesions of the VPL extending to the centrum medianum, central pain was rare. 2 cases with aphasia due to thalamic hemorrhage were found in this series, both in the dominant hemisphere. It is suggested that the thalamus in the dominant hemisphere may be related to speech and in the nondominant to a central pain mechanism.     

The significance of interhemispheric asymmetry in the development of compensatory processes in the human brain

For more precise definition of the role of hemispheric interconnections in mechanisms of human CNS compensation the intercentral relations of the electrical activity of the left and right cerebral hemispheres were studied on physiological model of focal interhemispheric asymmetry. Spectral-coherent EEG characteristics of 36 patients with tumoral damage of one hemisphere were studied in condition of chronic (prior to operation) and acute (early terms of postoperative period) brain decompensation. In was shown that the reorganization of the structure of the EEG intercentral relations correlated with definite stages of CNS compensatory processes and that the character of hemispheric interconnections depended on the lateralization of the damage focus. The primary role was revealed of the degree of the left (dominant) hemisphere preservation in restoration of normal pattern of the interhemispheric asymmetry of the coherence of human brain electrical processes.     

<Emphasis Type="Italic">PLP1</Emphasis> Gene Variation Modulates Leftward and Rightward Functional Hemispheric Asymmetries

Molecular neurobiological factors determining corpus callosum physiology and anatomy have been suggested to be one of the major factors determining functional hemispheric asymmetries. Recently, it was shown that allelic variations in two myelin-related genes, the proteolipid protein 1 gene PLP1 and the contactin 1 gene CNTN1, are associated with differences in interhemispheric integration. Here, we investigated whether three single nucleotide polymorphisms that were associated with interhemispheric integration via the corpus callosum in a previous study also are relevant for functional hemispheric asymmetries. To this end, we tested more than 900 healthy adults with the forced attention dichotic listening task, a paradigm to assess language lateralization and its modulation by cognitive control processes. Moreover, we used the line bisection task, a paradigm to assess functional hemispheric asymmetries in spatial attention. We found that a polymorphism in PLP1, but not CNTN1, was associated with performance differences in both tasks. Both functional hemispheric asymmetries and their modulation by cognitive control processes were affected. These findings suggest that both left and right hemisphere dominant cognitive functions can be modulated by allelic variation in genes affecting corpus callosum structure. Moreover, higher order cognitive processes may be relevant parameters when investigating the molecular basis of hemispheric asymmetries.     

Sensory lateralization in pain subjective perception for noxious heat stimulus

The aim of the present study was to identify and characterize hemispheric lateralization for pain intensity perception. A sample of 351 healthy volunteers was tested by the immersion of the right hand for 10 s followed by the same test for the left hand (RL group; n = 199) or in a random sequence (RND group; n = 152) into a water bath (48 degrees C, 15 s). Pain intensity was self-reported by the Visual Analogue Scale (VAS). The motor hemispherical Lateralization Index (LI) was obtained by the Edinburgh Inventory. Gender, hand skin fold, interstimulus time and menstrual cycle data in case of female subjects were recorded. The sample, 60.7% females and 39.3% males, 20.4 +/- 0.18 (mean +/- SEM) years old, showed 92.1% right-handed subjects. Left hand VAS was significantly higher than right hand VAS for RL (7.24 +/- 1.31 vs 6.74 +/- 1.52; p < 0.01) and RND (7.24 +/- 0.82 vs 6.73 +/- 1.25; p < 0.01) both for right- and left-handed subjects. A low but significant correlation for VAS scores and LI was found (r = 0.14; p < 0.05 or r = 0.18; p < 0.05, for left or right hand, respectively). Skin fold was statistically similar in both hands (p > 0.05) being highly correlated with each other (r = 0.68; p < 0.05). Pain subjective perception was not correlated to interstimulus time (r = -0.01; p > 0.05). Females showed significantly higher values than males for both left and right hand VAS scores. Periovulatory phase VAS value was significantly higher than luteal phase VAS only for the right hand test (7.57 +/- 0.20 vs 6.47 +/- 0.33; p < 0.01). The results of the present study suggest a lateralization of pain intensity perception to the right hemisphere not correlated with the motor hemispheric lateralization.     

Lateralization in feeding is food type specific and impacts feeding success in wild birds

Current research suggests that hemispheric lateralization has significant fitness consequences. Foraging, as a basic survival function, is a perfect research model to test the fitness impact of lateralization. However, our understanding of lateralized feeding behavior is based predominantly on laboratory studies, while the evidence from wild animals in natural settings is limited. Here we studied visual lateralization in yellow‐footed green pigeons (Treron phoenicoptera) feeding in the wild. We aimed to test whether different types of food objects requiring different searching strategies elicit different eye/hemisphere biases. When feeding on relatively large, uniformly colored food objects (mahua flowers) which can be present or absent in the viewed patch, the majority of pigeons relied mostly on the left eye–right hemisphere. In contrast, when feeding on smaller and more abundant food objects, with color cues signaling its ripeness (sacred figs), right‐eye (left‐hemisphere) preference prevailed. Our results demonstrate that oppositely directed visual biases previously found in different experimental tasks occur in natural feeding situations in the form of lateralized viewing strategies specific for different types of food. The results suggest that pigeons rely on the hemisphere providing more advantages for the consumption of the particular type of food objects, implying the relevance of brain lateralization as a plastic adaptation to ecological demands. We assessed the success of food discrimination and consumption to examine the link between lateralization and cognitive performance. The use of the preferred eye resulted in better discrimination of food items. Discrimination accuracy and feeding efficiency were significantly higher in lateralized individuals. The results showed that visual lateralization impacted pigeons’ feeding success, implicating important fitness benefits associated with lateralization.     

On the Interrelationship of Speech Functioning and Manual Motor Activity in Aphasia

Clinicians, physiologists, and psychologists are familiar with cases of simultaneous disturbance of various functions in localized cerebral lesions. These phenomena have been studied and described repeatedly, but continue to be of substantial interest, as analysis of them may make a contribution to the study of localization of functions in the cerebral cortex, substitution and restoration of functions, and the nature of their interrelationships. Our attention was attracted by a case of simultaneous disturbance of motor function and the power of speech in a lesion of the left (dominant) hemisphere. We began by investigating motor functions in aphasia and in the normal state, with a view to subsequent comparison of the motor and verbal functions in the normal state and in aphasia.     

Long-range temporal correlations of broadband EEG oscillations for depressed subjects following different hemispheric cerebral infarction

Abnormal long-range temporal correlation (LRTC) in EEG oscillation has been observed in several brain pathologies and mental disorders. This study examined the relationship between the LRTC of broadband EEG oscillation and depression following cerebral infarction with different hemispheric lesions to provide a novel insight into such depressive disorders. Resting EEGs of 16 channels in 18 depressed (9 left and 9 right lesions) and 21 non-depressed (11 left and 10 right lesions) subjects following cerebral infarction and 19 healthy control subjects were analysed by means of detrended fluctuation analysis, a quantitative measurement of LRTC. The difference among groups and the correlation between the severity of depression and LRTC in EEG oscillation were investigated by statistical analysis. The results showed that LRTC of broadband EEG oscillations in depressive subjects was still preserved but attenuated in right hemispheric lesion subjects especially in left pre-frontal and right inferior frontal and posterior temporal regions. Moreover, an association between the severity of psychiatric symptoms and the attenuation of the LRTC was found in frontal, central and temporal regions for stroke subjects with right lesions. A high discriminating ability of the LRTC in the frontal and central regions to distinguish depressive from non-depressive subjects suggested potential feasibility for LRTC as an assessment indicator for depression following right hemispheric cerebral infarction. Different performance of temporal correlation in depressed subjects following the two hemispheric lesions implied complex association between depression and stroke lesion location.     

Alterations in Cortical Morphology after Neonatal Stroke: Compensation in the Contralesional Hemisphere?

Although neonatal arterial ischemic stroke is now well‐studied, its complex consequences on long‐term cortical brain development has not yet been solved. In order to understand the brain development after focal early brain lesion, brain morphometry needs to be evaluated using structural parameters. In this work, our aim was to study and analyze the changes in morphometry of ipsi‐ and contralesional hemispheres in seven‐year‐old children following neonatal stroke. Therefore, we used surface‐based morphometry in order to examine the cortical thickness, surface area, cortical volume, and local gyrification index in two groups of children that suffered from neonatal stroke in the left (n = 19) and right hemispheres (n = 15) and a group of healthy controls (n = 30). Reduced cortical thickness, surface area, and cortical volumes were observed in the ipsilesional hemispheres for both groups in comparison with controls. For the group with left‐sided lesions, higher gyrification of the contralesional hemisphere was observed primarily in the occipital region along with higher surface area and cortical volume. As for the group with right‐sided lesions, higher gyrification was detected in two separate clusters also in the occipital lobe of the contralesional hemisphere, without a significant change in cortical thickness, surface area, or cortical volume. This is the first time that alterations of structural parameters are detected in the “healthy” hemisphere after unilateral neonatal stroke indicative of a compensatory phenomenon. Moreover, findings presented in this work suggest that lesion lateralization might have an influence on brain development and maturation.     

Sex‐specific lateralization during aggressive interactions in breeding king penguins

Brain and behavioral asymmetries (termed "lateralization"; e.g., preferential eye‐use) have been mostly described in controlled laboratory conditions, although striking similarities of hemispheric brain control for specific behaviors have also been shown in the wild. Visual lateralization may provide ecological advantages by allowing complementary roles played by the left–right lateral and frontal visual field in distant or close motion detection of predators or other threats. In this study, we tested for lateralization in aggressive behavior in wild king penguins (Aptenodytes patagonicus), seabirds breeding in a context of strong colonial aggressiveness, and subject to on‐land‐based predation of their egg or chick. We show that males initiated more agonistic interactions when a congener was located in their right frontal visual field and in their left lateral visual field. The results obtained in females were the exact opposite for each subdivision of their visual fields. Complementary lateralization in male and female penguins may be part of a more general phenomenon, allowing partners to coordinate their behavior during reproduction. This may be especially true during the period of courtship, during which these seasonally monogamous and monomorphic seabirds engage in mutual mate choice based on a complex and ritualized display of ornaments located on the left and right lateral sides of the head. Those results open exciting questions as to whether hemispheric control of aggression is a commonly selected phenotypic trait across colonial seabirds.     

Interhemispheric motor asymmetry of conditioned feedback

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

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.     

Sensory lateralization in pain subjective perception for noxious heat stimulus

The aim of the present study was to identify and characterize hemispheric lateralization for pain intensity perception. A sample of 351 healthy volunteers was tested by the immersion of the right hand for 10 s followed by the same test for the left hand (RL group; n = 199) or in a random sequence (RND group; n = 152) into a water bath (48°C, 15 s). Pain intensity was self-reported by the Visual Analogue Scale (VAS). The motor hemispherical Lateralization Index (LI) was obtained by the Edinburgh Inventory. Gender, hand skin fold, interstimulus time and menstrual cycle data in case of female subjects were recorded. The sample, 60.7% females and 39.3% males, 20.4 &#45 0.18 (mean &#45 SEM) years old, showed 92.1% right-handed subjects. Left hand VAS was significantly higher than right hand VAS for RL (7.24 &#45 1.31 vs 6.74 &#45 1.52; p < 0.01) and RND (7.24 &#45 0.82 vs 6.73 &#45 1.25; p < 0.01) both for right- and left-handed subjects. A low but significant correlation for VAS scores and LI was found ( r = 0.14; p < 0.05 or r = 0.18; p < 0.05, for left or right hand, respectively). Skin fold was statistically similar in both hands ( p > 0.05) being highly correlated with each other ( r = 0.68; p < 0.05). Pain subjective perception was not correlated to interstimulus time ( r = -0.01; p > 0.05). Females showed significantly higher values than males for both left and right hand VAS scores. Periovulatory phase VAS value was significantly higher than luteal phase VAS only for the right hand test (7.57 &#45 0.20 vs 6.47 &#45 0.33; p < 0.01). The results of the present study suggest a lateralization of pain intensity perception to the right hemisphere not correlated with the motor hemispheric lateralization.