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PubMed2003

Temporary and permanent signs of interhemispheric disconnection after traumatic brain injury.

The corpus callosum is frequently damaged by closed head traumas, and the resulting deficits of interhemispheric communication may vary according to the specific position of the lesion within the corpus callosum. This paper describes a single case who suffered a severe traumatic brain injury resulting in a lesion of the posterior body of the corpus callosum. Among the classical symptoms of interhemispheric disconnection, left hand anomia, left upper limb ideomotor dyspraxia, left visual field dyslexia and dysnomia, and left ear suppression in a dichotic listening task were observed shortly after the injury but recovered completely or almost completely with the passage of time. The only symptom of interhemispheric disconnection which was found to persist more than 4 years after the injury was an abnormal prolongation of the crossed-uncrossed difference in a simple visuomotor reaction time task. This prolongation was comparable with that observed in subjects with complete callosal lesions or agenesis. The results suggest that the posterior body of the corpus callosum may be an obligatory interhemispheric communication channel for mediating fast visuo-motor responses. The transient nature of other symptoms of interhemispheric disconnection suggests a relatively wide dispersion of fibers with different functions through the callosal body, such that parts of them can survive a restricted lesion and allow functional recovery of hemispheric interactions. An assessment of the evolution in time of symptoms of interhemispheric disconnection following restricted callosal lesions may reveal fine and coarse features of the anatomo-functional topography of the corpus callosum.

Adult↗
PubMed2000

The acallosal mouse strain I/LnJ: a putative model of ADHD?

ADHD has been sometimes associated to a defective interhemispheric cross-talk caused by hypoplasia of the corpus callosum. The inbred mouse strain I/LnJ shows total callosal agenesis with complete penetrance, and behavioral features which resemble ADHD. In conditioned learning tasks, as well as in paradigms of spontaneous behavior. I/LnJ mice, as compared to other inbred strains, show lower learning scores, impulsiveness, and significantly higher locomotor activity, albeit with considerable individual variations. In order to disentangle the influences of the genetic background from the effects of the callosal agenesis, we undertook crossing studies between I/LnJ and C57BL/6 mice, obtaining hybrids with missing corpus callosum. In comparison to normal C57BL/6 mice, acallosal hybrids exposed to a novel open-field showed a different locomotor pattern, with less short stops and more center crossing during the beginning of the session. In a metabolic mapping study, the tendency of acallosals to stay off the walls was found to be associated to lower 2-deoxyglucose uptake in the left striatum and cerebral cortex, while the number of short stops was correlated to the bilateral levels of 2-deoxyglucose uptake in the frontal and parietal cortex. The results hint at a right hemisphere dominance in impulsiveness and hyperactivity, boosted by the lack of callosal connections.

Agenesis of Corpus Callosum↗
PubMed1998

Effects of clinorotation on the polysaccharide content of resynthesized walls of protoplasts.

Changes in cellulose and callose content during cell wall regeneration in Brassica oleracea protoplasts have been examined by cytofluorimetry following their exposure to the conditions of the horizontal clinostat (2 r.p.m.) for 10 days. In comparison with controls, cellulose content decreased 4-fold and 28% of the protoplasts failed to resynthesize a wall in the clinorotated sample. The callose content was almost doubled in clinostated cells. Callose synthesis fluctuated in both control and clinorotated protoplasts. The results support the idea that inhibition of cellulose synthesis in protoplasts grown on the clinostat is caused by a change of plasmalemma fluidity and functioning, and also by a disturbance to the state of cytoplasmic calcium under conditions of simulated microgravity.

Brassica↗
PubMed2000

Comparative study of inter- and intrahemispheric somatosensory functions in children with partial and complete agenesis of the corpus callosum.

Inter- and intrahemispheric somatosensory functions were evaluated in blinded tests of 11 children with partial and complete agenesis of the corpus callosum (age range 2 years 8 months to 11 years 9 months) and compared with those of age- and sex-matched control individuals both normally developing and with neurological impairment. Tests included uni- and bimanual measures of stereognosis, haptic visual discrimination, kinaesthesis, and texture matching. Children with callosal absence displayed significant difficulties with many somatosensory functions, but most deficits were no greater than those of the children who had neurological dysfunction and an intact corpus callosum. Children with callosal absence, however, had significantly greater difficulty with bimanual texture matching, seemingly because this task required refined spatial interpretation of somatosensory input. Response times for the individuals with callosal absence were significantly greater than those for control participants with neurological impairment on several tasks in which overall accuracy of performance among groups did not significantly differ. These findings suggest that children with agenesis of the corpus callosum may have less efficient and slower processing capacity for certain types of somatosensory information. Possible compensatory mechanisms are discussed.

Agenesis of Corpus Callosum↗
PubMed1991

Visual-field map in the transcallosal sending zone of area 17 in the cat.

The representation of the visual field in the part of area 17 containing neurons that project axons across the corpus callosum to the contralateral hemisphere was defined in the cat. Of 1424 sites sampled along 77 electrode tracks, 768 proved to be in the callosal sending zone, which was identified by retrograde transport of horseradish peroxidase that had been deposited in the opposite hemisphere. The results show that the callosal sending zone has a fairly constant width of between 3 and 4 mm at most levels in area 17. However, the representation of the contralateral field at the different elevations of the visual field is not equal in this zone. The zone represents positions within 4 deg of the midline at the 0-deg horizontal meridian, and positions out to 15-deg azimuths in the upper hemifield and out to positions of 25-deg azimuth in the lower hemifield. The shape of the representation is approximately mirror-symmetric about the horizontal meridian, although there is a greater extent in the lower hemifield, which can be accounted for by the greater range of elevations (greater than 60 deg) represented there compared with the upper hemifield (approximately 40 deg). The representation in the sending zone of one hemisphere matches that present in the area 17/18 transition zone, which receives the bulk of transcallosal projections, in the opposite hemisphere. The observations on the sending zone show that callosal connections of area 17 are concerned with a vertical hour-glass-shaped region of the visual field centered on the midline. The observations suggest that in addition to interactions between neurons concerned with positions immediately adjacent to the midline, there are positions, especially high and low in the visual field, where interactions can occur between neurons that have receptive fields displaced some distance from the midline.

Animals↗
PubMed1982

Single cortical neurones have axon collaterals to ipsilateral and contralateral cortex in fetal and adult primates.

In the adult brain, cortical neurones that project to other cortical areas have traditionally been classified as either "associational' (having connections with the ipsilateral hemisphere) or "callosal' (projecting to areas in the contralateral hemisphere). Using double-labelling with fluorescent dyes, we have now identified a novel category of mature cortical neurone that has both an "associational' and a "callosal' axon. Such neurones can direct their callosal axons either to a cytoarchitectonic area homotopic to the one in which their cell bodies reside or to an entirely different heterotopic region in the contralateral hemisphere. These cortical neurones with divergent axon collaterals in the adult neocortex differ from recently described neurones that have two axons only transiently during development.

Animals↗
PubMed1997

Development of fetal gyri, sulci and fissures: a transvaginal sonographic study.

We aimed to determine the feasibility of imaging specific sulci, gyri and fissures using transvaginal sonography and to correlate their first sonographic recognition with gestational age. Retrospectively, 262 fetal brain scans were analyzed from a total of 337 scans. Scans were selected if any of the following structures were seen: in the coronal plane the lateral, callosal and cingulate sulcus and gyrus; in the median plane the parieto-occipital and calcarine fissures, and the cingulate gyrus and sulcus; and, in an oblique section, the lateral sulcus. The gestational age at which the fissures, sulci and gyri were first imaged was recorded and subsequently compared with similar anatomical studies from the literature. It was possible to identify all the targeted structures. The gestational ages at which the structures were first imaged were: the callosal sulcus, from 14 weeks; the lateral sulcus, from 18 weeks; the parieto-occipital sulcus and calcarine fissure, from 18 weeks; and the cingulate gyrus, from 26 weeks. We concluded that the developmental maturation of the normal fetal brain follows a predictable timetable, and that this maturation can be grossly followed with sonography. The sonographic recognition of the fissures, gyri and sulci lagged behind the observations by anatomical studies. The greatest discrepancy was the first appearance of the cingulate gyrus which, in the anatomical studies, could be seen by 18 postmenstrual weeks and, in our study, was seen after 26 postmenstrual weeks. The one exception was the callosal sulcus, which was first seen at 14 postmenstrual weeks in both the sonographic and anatomical studies. In conclusion, the recognition of specific structures of the cortical map is possible. Sonography may be used to image the developing cortical surface.

Brain↗
PubMed2002

Agenesis and dysgenesis of the corpus callosum.

Agenesis and dysgenesis of the corpus callosum is a frequent anomaly that presents with a spectrum of clinical features and exhibits variable findings in neurological studies. Clinical signs and symptoms are the result of cerebral and extracerebral malformations associated with callosal dysgenesis. Callosal agenesis may be an isolated anomaly or may be syndromic as part of more extensive malformations, metabolic and genetic disorders. The advent of modern techniques and equipment for neuroimaging have allowed us to define with more precision the type and severity of the callosal dysgenesis and accompanying other cerebral malformations. Molecular genetic studies allow the recognition and confirmation of new syndromes that until now were incompletely defined. In the context of these new pathologic entities, a new classification is proposed that may prove to be more useful than the traditional single category, "agenesis of the corpus callosum" and can serve as a basis for a later, more detailed, etiologic classification that integrates morphology and molecular genetics.

Agenesis of Corpus Callosum↗
PubMed1995

Cytokinesis in tobacco BY-2 and root tip cells: a new model of cell plate formation in higher plants.

Cell plate formation in tobacco root tips and synchronized dividing suspension cultured tobacco BY-2 cells was examined using cryofixation and immunocytochemical methods. Due to the much improved preservation of the cells, many new structural intermediates have been resolved, which has led to a new model of cell plate formation in higher plants. Our electron micrographs demonstrate that cell plate formation consists of the following stages: (1) the arrival of Golgi-derived vesicles in the equatorial plane, (2) the formation of thin (20 +/- 6 nm) tubes that grow out of individual vesicles and fuse with others giving rise to a continuous, interwoven, tubulo-vesicular network, (3) the consolidation of the tubulo-vesicular network into an interwoven smooth tubular network rich in callose and then into a fenestrated plate-like structure, (4) the formation of hundreds of finger-like projections at the margins of the cell plate that fuse with the parent cell membrane, and (5) cell plate maturation that includes closing of the plate fenestrae and cellulose synthesis. Although this is a temporal chain of events, a developing cell plate may be simultaneously involved in all of these stages because cell plate formation starts in the cell center and then progresses centrifugally towards the cell periphery. The "leading edge" of the expanding cell plate is associated with the phragmoplast microtubule domain that becomes concentrically displaced during this process. Thus, cell plate formation can be summarized into two phases: first the formation of a membrane network in association with the phragmoplast microtubule domain; second, cell wall assembly within this network after displacement of the microtubules. The phragmoplast microtubules end in a filamentous matrix that encompasses the delicate tubulo-vesicular networks but not the tubular networks and fenestrated plates. Clathrin-coated buds/vesicles and multivesicular bodies are also typical features of the network stages of cell plate formation, suggesting that excess membrane material may be recycled in a selective manner. Immunolabeling data indicate that callose is the predominant lumenal component of forming cell plates and that it forms a coat-like structure on the membrane surface. We postulate that callose both helps to mechanically stabilize the early delicate membrane networks of forming cell plates, and to create a spreading force that widens the tubules and converts them into plate-like structures. Cellulose is first detected in the late smooth tubular network stage and its appearance seems to coincide with the flattening and stiffening of the cell plate.

Cell Division↗
PubMed1981

Disorganization and reorganization of cognitive and sensorimotor functions in cerebral commissurotomy. Compensatory roles of the forebrain commissures and cerebral hemispheres in man.

Neuropsychological studies of 10 patients with complete cerebral commissurotomy and 2 with frontal commissurotomy showed differences in the nature and severity of pre-operative, initial and long-term post-operative deficits in verbal and nonverbal cognitive, memory, and sensorimotor functions. Neurosurgical findings before and after operation recorded various types of extra-callosal brain damage in all 12 patients, including 4 with gross structural lesions in the right hemisphere before surgery. Our findings revealed that differences in the nature and severity of pre-operative and post-operative deficits varied according to the nature and laterality of associated extra-callosal damage before as well as after operation. Following complete commissurotomy, all 4 patients with pre-operative structural lesions of the right hemisphere revealed a unique pattern of marked, selective impairment of nonverbal cognitive functions strikingly similar to the effects of right hemispherectomy for tumour in adults. The remaining 8 patients showed systematic patterns of greater impairment in verbal and nonverbal cognitive and contralateral sensorimotor functions, depending on the laterality of extra-callosal damage. The significantly higher pre-operative Wechsler Performance IQs of the 4 patients with structural lesions of the right hemisphere suggest that following earlier damage to the right hemisphere, the forebrain commissures contribute to a reorganization of interhemispheric relations to permit restitution of the diminished nonverbal cognitive functions resulting from damage to the right hemisphere. Thus, in addition to other possible roles in integrating the functions of the two hemispheres in the normal brain, the forebrain commissures can also serve as 'standby' or 'reserve' structures for reorganization of compensatory interhemispheric mechanisms following lateralized brain insults. Since some patients showed later postoperative improvement, the extent of ultimate competence and the 'cognitive costs' of commissurotomy can only be defined by continuing follow-up studies. Apart from their practical clinical implications, such studies may also contribute to elucidation of the principles underlying the organization, disorganization and reorganization of human brain functions.

Adolescent↗
PubMed1995

Channels of the corpus callosum. Evidence from simple reaction times to lateralized flashes in the normal and the split brain.

We studied 75 normal subjects and three commissurotomized patients using unimanual simple reaction times to lateralized flashes as a behavioural estimate of interhemispheric transmission time. Three different versions of the paradigm were performed: (i) the basic task; (ii) a motor task, with an increased complexity of the motor response; and (iii) a visual task, with an increased complexity of the visual stimulus presentation. We tested two hypotheses. First, that the new versions of the simple reaction time task result in shifts in hemispheric specialization for processing motor output (indicated by a main effect of response hand) or visual input (indicated by a main effect of visual field) alone, without affecting callosal transmission. In that case normals and split brain patients would show no significant task by response hand by visual field interaction and no significant task by crossed-uncrossed difference interaction. Secondly, that the new versions of the task affect callosal transfer. In that case, normals, but not split brain patients, would show a significant task by response hand by visual field interaction and a significant task by crossed-uncrossed difference interaction. Results are consistent with the latter hypothesis, showing that the motor task significantly changed the response hand by visual field interaction and the crossed-uncrossed difference, but only in normal subjects, perhaps producing a switch in the callosal channel subserving the interhemispheric transfer.

Adult↗
PubMed2000

The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients.

A standard model of word reading postulates that visual information is initially processed by occipitotemporal areas contralateral to the stimulated hemifield, from whence it is subsequently transferred to the visual word form (VWF) system, a left inferior temporal region specifically devoted to the processing of letter strings. For stimuli displayed in the left visual field, this transfer proceeds from the right to the left hemisphere through the posterior portion of the corpus callosum. In order to characterize the spatial and temporal organization of these processes, reading tasks with split-field presentation were performed by five control subjects and by two patients suffering from left hemialexia following posterior callosal lesions. The subjects' responses were studied using behavioural measures and functional brain imaging techniques, providing both high spatial resolution (functional MRI, fMRI) and high temporal resolution (high-density event-related potentials, ERPs). Early visual processing was revealed as activations contralateral to stimulation, located by fMRI in the inferior occipitotemporal region and presumably coincident with area V4. A negative wave occurring 150-160 ms post-stimulus, also strictly contralateral to stimulation, was recorded over posterior electrodes. In contrast with these hemifield-dependent effects, the VWF system was revealed as a strictly left-hemispheric activation which, in control subjects, was identical for stimuli presented in the left or in the right hemifield and was located in the middle portion of the left fusiform gyrus. The electrical signature of the VWF system consisted of a unilateral sharp negativity, recorded 180-200 ms post-stimulus over left inferior temporal electrodes. In callosal patients, due to the inability of visual information to pass across the posterior part of the corpus callosum, the VWF system was activated only by stimuli presented in the right visual field. Similarly, a significant influence of the word/non-word status on ERPs recorded over the left hemisphere was discernible for either hemifield in controls, while it affected only right-hemifield stimuli in callosal patients. These findings provide direct support for the main components of the classical model of reading and help specify their timing and cerebral substrates.

Adult↗
PubMed2000

Regional size reduction in the human corpus callosum following pre- and perinatal brain injury.

This morphometric study examined two aspects of corpus callosum development: pediatric cortico-callosal topography and developmental neuroplasticity subsequent to perinatal brain injury. In vivo magnetic resonance imaging was used to quantify the total midsagittal cross-sectional area and five anterioposterior subregions of the callosum in 10 children with focal lesions and 86 healthy volunteer control subjects. Nine of the ten children with early injury showed a reduction in the total area of the callosum relative to matched controls. The area of the total callosum cross-section was inversely proportional to the size of lesion. All patients displayed region-specific size reduction. This regional thinning bore a topographical relationship to the lesion sites. Reduction in anterior subregions 1, 2 and 3 was respectively associated with lesions in the anterior inferior frontal area, the middle and superior frontal region, and the precentral area. Attenuation of subregion 4 corresponded to anterior parietal lesions, and thinning of subregion 5 occurred with posterior parietal injury. This cortical-callosal pattern coincides with adult and nonhuman primate mappings. Callosal thinning despite the early onset of the lesions suggests limits to developmental neuroplasticity.

Adolescent↗
PubMed2004

Frontal-hippocampal double dissociation between normal aging and Alzheimer's disease.

Controversy persists regarding whether Alzheimer's disease (AD) is a distinct entity or instead exists on a continuum with nondemented aging. To explore this issue, volumetric analyses of callosal and hippocampal regions were performed on 150 participants aged 18-93 years. Group-level analyses revealed that nondemented age-related differences were greater in anterior than posterior callosal regions and were not augmented by early-stage AD. In contrast, early-stage AD was associated with substantial reduction in hippocampal volume. Examination of the 100 older adults using regression analyses demonstrated age-associated differences in callosal volume that were similar in demented and nondemented individuals. Early-stage AD was again characterized by a marked reduction in hippocampal volume while age alone induced only mild differences in hippocampal volume. As a final analysis, the formal double dissociation was confirmed by comparing the effects of age directly against the effects of dementia. These results suggest a multiple-component model of aging. One process, associated with AD, manifests early and prominently in the medial temporal lobe. A separate process, ubiquitous in aging, affects brain white matter with an anterior-to-posterior gradient and may underlie the executive difficulties common in aging.

Adolescent↗
PubMed1997

Interrelationships between cytoplasmic Ca2+ peaks, pollen hydration and plasma membrane conductances during compatible and incompatible pollinations of Brassica napus papillae.

We have investigated Ca(2+)-involving cell signaling, plasma membrane potentials and conductances and callose formation during early stages of pollination of papillae of Brassica napus. Using fluorescence imaging of calcium green-1, we found that application of a range of pollen types and controls all rapidly produced small localized peaks in papillar cytoplasmic [Ca2+]. This response was more frequent in compatible than incompatible interactions and was correlated with subsequent hydration of the applied pollen grains, indicating that it may be a differential prerequisite of the compatible signaling pathway leading to successful pollinations. In contrast, a slight trend to increased plasma membrane conductance (but with no indications of action potential-like responses) and also callose deposition in papillae adjacent to pollen grains followed pollination in both SC and SI interactions, indicating that alterations in plasma membrane permeability and callose deposition during early phases of pollination are not primary determinants of the fate of attempted pollinations.

Brassica↗
PubMed2006

Nonhost resistance in Arabidopsis-Colletotrichum interactions acts at the cell periphery and requires actin filament function.

Pathogenesis of nonadapted fungal pathogens is often terminated coincident with their attempted penetration into epidermal cells of nonhost plants. The genus Colletotrichum represents an economically important group of fungal plant pathogens that are amenable to molecular genetic analysis. Here, we investigated interactions between Arabidopsis and Colletotrichum to gain insights in plant and pathogen processes activating nonhost resistance responses. Three tested nonadapted Colletotrichum species differentiated melanized appressoria on Arabidopsis leaves but failed to form intracellular hyphae. Plant cells responded to Colletotrichum invasion attempts by the formation of PMR4/GSL5-dependent papillary callose. Appressorium differentiation and melanization were insufficient to trigger this localized plant cell response, but analysis of nonpathogenic C. lagenarium mutants implicates penetration-peg formation as the inductive cue. We show that Arabidopsis PEN1 syntaxin controls timely accumulation of papillary callose but is functionally dispensable for effective preinvasion (penetration) resistance in nonhost interactions. Consistent with this observation, green fluorescent protein-tagged PEN1 did not accumulate at sites of attempted penetration by either adapted or nonadapted Colletotrichum species, in contrast to the pronounced focal accumulations of PEN1 associated with entry of powdery mildews. We observed extensive reorganization of actin microfilaments leading to polar orientation of large actin bundles towards appressorial contact sites in interactions with the nonadapted Colletotrichum species. Pharmacological inhibition of actin filament function indicates a functional contribution of the actin cytoskeleton for both preinvasion resistance and papillary callose formation. Interestingly, the incidence of papilla formation at entry sites was greatly reduced in interactions with C. higginsianum isolates, indicating that this adapted pathogen may suppress preinvasion resistance at the cell periphery.

Actin Cytoskeleton↗
PubMed1994

Interhemispheric transfer time and corpus callosum size.

We examined the relationship between the size of five mid-sagittal corpus callosum subareas (measured with in vivo magnetic resonance morphometry) and hand reaction times at dichotic consonant-vowel monitoring in fifty healthy young adults. Based on the reaction times, interhemispheric transfer times between auditory and motor brain areas were calculated and related to anterior and posterior corpus callosum subarea measurements. We found no relationship between the size of callosal subareas and auditory or motor interhemispheric transfer times. We did, however, find a significant correlation between mean reaction time and total corpus callosum size. Our results suggest that normal variation in callosal size or shape is not related to individual differences in auditory lateralization. Instead, callosal size may be associated with speed of information processing.

Adult↗
PubMed1996

Age-related changes in fibre composition of the human corpus callosum: sex differences.

We found positive correlations between the number of myelinated callosal fibres > 1 micron in diameter and age in humans. The relatively abundant axons with diameters between 1 and 3 microns correlated with age only in females, while the scarce fibres > 3 microns in diameter correlated significantly with age only in males. When analysing different callosal segments, it was found that in the midbody (but not in the splenium) of females the number of fibres > 3 microns also increased with age. In males, the relationship between these large diameter fibres and age disappeared after dividing the callosum into distinct segments. There may, therefore, be sex differences in the course of callosal fibre growth and myelination during the normal lifespan.

Adult↗