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PubMed1998

Abnormal callosal morphology in male adult dyslexics: relationships to handedness and phonological abilities.

The classical notion that developmental dyslexia may somehow relate to impaired communication between hemispheres has not yet received convincing support. Sixteen dyslexic adults and 12 controls received a high resolution brain MRI scan for morphometric study of the corpus callosum. Automatized measurements of callosal area and calculation of indices defining the general morphology of the callosal mid-surface were performed. Each participant received global intelligence and reading achievement evaluation; dyslexics were further proposed specific neuropsychological tests specially designed to explore the mechanisms of reading impairment. It just appears from the group comparisons (1) that the dyslexics' corpus callosum displays a more circular and evenly thicker general shape, and (2) that the midsagittal surface is on the average larger than in controls, in particular in the isthmus. Moreover, the different morphometric characteristics of the dyslexic brain correlated with the degree of impairment on various tests exploring phonological abilities. In vivo morphometry of the corpus callosum may provide valuable hints for understanding developmental learning disorders and their consequences in adults.

Adolescent↗
PubMed1993

Functional alterations induced by prenatal malnutrition in callosal connections and interhemispheric asymmetry as revealed by transcallosal and visual evoked responses in the rat.

It is known that nutritional restriction during gestation affects the growth of the corpus callosum. The present study was designed to evaluate whether prenatal malnutrition may alter, in the rat, the normal pattern of functional callosal interhemispheric connections of the visual cortex. Since callosal development has been associated with brain lateralization, the effect of malnutrition during gestation on the normal asymmetry of visual cortical evoked responses was also studied. Prenatal malnutrition was induced by restricting food consumption by pregnant rats (10 g daily) from Day 8 post-conception to parturition. Results of experiments performed on 45- to 50-day-old offspring showed that the starvation treatment (i) reduced both the peak-to-peak amplitude and the extent of the projecting field of transcallosal evoked responses, and (ii) abolished the normal brain interhemispheric asymmetry of visual evoked responses. These effects are discussed in relationship to regressive events occurring during synaptogenesis, which are known to play key roles in establishing the adult structure and functional properties of the corpus callosum.

Animals↗
PubMed1995

Partial seizures with onset in central area: use of the callosal grid system for localization.

Focal seizures arising in the central area require precise anatomic and physiologic mapping of ictal onset. The central sulcus is identified by the callosal grid system whose mid-vertical plane identifies the central sulcus inferiority where the central artery passes into the central sulcus. 5 patients with intractable seizures of central origin where localized with this method. Extent of resection was confirmed on postoperative NRI. The subdural grid was accurately placed on the central sulcus, confirmed by electrophysiologic means. Grid planes compartmentalized ictal onset, and post-operative resection correlated precisely. All patients are seizure-free. Seizures arising in the central area, precisely located, can be treated with good to excellent results. Localization of onset is facilitated by use of the callosal grid system, and allows superimposition of pre-, intra- and post-operative anatomic and physiologic data.

Adolescent↗
PubMed1985

Modification of callosal afferents of the primary visual cortex ipsilateral to the remaining eye in rats monocularly enucleated at different stages of ontogeny.

Callosal afferents to the primary visual cortex (area Oc1) mainly originate in the border region between the lateral portion of the primary visual cortex (area Oc1) and the laterally positioned secondary visual cortex (area Oc2L) of the contralateral hemisphere. The extent of this region has been determined by retrograde labeling with horseradish peroxidase (HRP). In normal rats the width of the retrogradely labeled cortical strip is about 0.3 mm. In rats monocularly enucleated from the 23rd up to the 44th ontogenetic day and subsequently injected as adults with HRP into Oc1 ipsilateral to the remaining eye, the perikarya of the callosal afferents from the opposite hemisphere are labeled in the form of significantly wider columns (about 0.8 mm) than in animals enucleated from the 50th ontogenetic day onwards. The latter do not differ from controls.

Afferent Pathways↗
PubMed1978

The retinotopic distribution of visual callosal projections in the suprasylvian visual areas compared to the classical visual areas (17, 18, 19) in the cat.

The distribution of the interhemispheric projection from area 17 and 18 was studied using the anterograde degeneration technique. Besides the classical visual areas (17, 18, 19), area 21 and several visual areas in the middle suprasylvian sulcus also received visual callosal input. In the four terminal areas of the middle suprasylvian sulcus the projection was found to be focused on representations of the ventrical meridian including the area centralis, as in the classical visual areas. An increase of the width of visual field represented in the zone of callosal terminations can be seen from area 17 through area 18 to area 19 and possibly this trend continues in the suprasylvian visual areas.

Animals↗
PubMed1981

The postnatal development of somatosensory callosal connections after partial lesions of somatosensory areas.

The distribution of S1 (first somatosensory area) and S2 (second somatosensory area) neurons projecting to the contralateral S2 was studied with horseradish peroxidase in normal adult cats and in cats aged between 129 and 248 days in which the injected S2 area had been deprived of some of its input by an earlier lesion (on postnatal days 3 to 30; day of birth = day 1) of ipsilateral S1, alone or combined with a lesion of contralateral S2. In animals with S1 lesions, as in the normal controls, labeled neurons were selectively distributed to the regions of the trunk representation and to parts of the forelimb and hindlimb representations; however, the normally acallosal region in the forepaw representation contained scattered labeled neurons in three of the four animals whose S1 had been lesioned during the first postnatal week. In these animals, the distribution of labeled neurons in the contralateral S2 was apparently normal. Furthermore, the additional lesion of this area during the first postnatal week (one animal) did not increase the degree of filling-in of the normally acallosal parts of S1. The partial filling-in of the acallosal parts of S1 is probably due to the preservation to adulthood of some of the callosal neurons which are present in these regions during the early postnatal life. Possibly, these neurons did not disappear (or lose their callosal axons) because the neonatal lesion (i) allowed their successful competition for terminal space in contralateral S2 or (ii) induced a reorganization of the peripheral input to this area.

Afferent Pathways↗
PubMed1981

Callosal projections of the striate cortex in the neonatal rabbit.

Callosal fiber projections of the striate cortex were studied in newborn rabbits using the methods of 1) retrograde transport of horseradish peroxidase (HRP) and 2) orthograde transport of tritiated leucine. Data collected from 6-8 day old animals revealed not only the existence of adult-like commissural fibers in the lateral striate cortex bordering the occipital area, but also an aberrant callosal projection from the medial striate cortex, an area not known to have any commissural fibers in the adult brain of those mammalian species studied.

Afferent Pathways↗
PubMed1980

A direct pathway from thalamus to visual callosal neurons in cat.

Horseradish peroxidase was injected in the right visual cortex and a large electrolytic lesion made in the left lateral geniculate nucleus of an adult cat. Neurons of origin of the callosal projection to the injected cortex were identified by retrograde labelling and selected for electron microscopic study. Degenerating thalamo-cortical axon terminals were found to contact a labelled stellate cell in layer IV and a labelled pyramidal cell in layer III at the border region of areas 17 and 18. We conclude that there is a monosynaptic pathway from lateral geniculate nucleus to the cells of origin of callosal axons to the contralateral visual cortex.

Animals↗
PubMed1988

Callosal projections between areas 17 in the adult tree shrew (Tupaia belangeri).

In the primary visual cortex (area 17) of the tree shrew (Tupaia belangeri) neurons projecting to the contralateral area 17 via the corpus callosum were identified by horseradish peroxidase histochemistry (HRP, WGA-HRP). The distribution of homotopic and heterotopic connections was studied. We found that a narrow stripe of area 17 close to the dorsal area 17/18 border - which corresponds to the visual field along the vertical meridian - is connected via homotopic callosal projections. The adjacent dorsal part of area 17, which largely corresponds to the binocular visual field, is connected via homotopic as well as heterotopic projections. Heterotopic projections originate in the cortical stripe along the area 17/18 border and their contralateral targets are displaced medially. Callosal neurons are located mostly in supragranular but also occur in infragranular layers. The supragranular neurons in general are pyramidal cells. In addition to these findings, we confirmed earlier reports on ipsilateral projections of the primary visual area to the dLGN, the claustrum, area 18 and other visual areas.

Animals↗
PubMed1986

The size of the zone of origin of callosal afferents projecting to the primary visual cortex contralateral to the remaining eye in rats monocularly enucleated at different postnatal ages.

The cortical zone from which callosal afferents projecting to the primary visual cortex (area Oc1) originate was studied in monocularly enucleated and normal rats. The extent of this cortical strip was determined by retrograde labeling with HRP and by measurement of its width in coronal sections. Albino rats were monocularly enucleated from the 23rd ontogenetic day to the 120th and iontophoretical injections into Oc1 contralateral to the remaining eye were done more than one year after enucleation. The width of the labeled strip of perikarya in the hemisphere ipsilateral to the remaining eye was largest in neonatally enucleated rats (about 1.1 mm) and declined with increasing age at which enucleation was performed. Additionally, the perikarya of callosal afferents in the hemisphere ipsilateral to the remaining eye in rats enucleated as young adults (90th and 120th ontogenetic day) were labeled in significantly wider strips (about 0.6 mm) than in unoperated control rats (about 0.4 mm).

Afferent Pathways↗
PubMed2000

Effects of reversible block of callosal afferent inputs on the response characteristics of single neurons in the cortical taste area in rats.

We examined the change in magnitude of the taste responses of single neurons in the cortical taste area (CTA) in one side by reversibly blocking the CTA in the other side with a local anesthetic, procaine-HCl, in urethane-anesthetized rats. Taste responses of 68 taste neurons were continuously recorded for up to 2 h until recovery from the treatment, and those in 50 of them were found to be affected significantly. No remarkable difference was noted in the spatial distribution of the affected and non-affected neurons in the CTA. Many of the affected neurons were located in layers IV and V of area GI and in layer V of area DI. In most cases, changes in the taste responses of single neurons were in one direction, i.e., either a decrease or an increase, but in a few cases they decreased or increased depending on the stimulus. The taste profile of callosal inputs was estimated by subtracting responses after treatment from the control responses before treatment. The results suggest that the CTAs on both sides are functionally connected by way of callosal fibers as anatomical studies indicate, and that the CTA in one side receives excitatory or inhibitory inputs from the other side.

Anesthetics, Local↗
PubMed2000

Interhemispheric transfer of visual motion information after a posterior callosal lesion: a neuropsychological and fMRI study.

Interhemispheric transfer of visual information was investigated behaviourally and with functional magnetic resonance imaging (fMRI) 6 months after a lesion of the posterior two-thirds of the corpus callosum. On tachistoscopical left hemifield presentation, the patient was severely impaired in reading letters, words and geographical names and moderately impaired in naming pictures and colours. In contrast, interhemispheric transfer of visual motion information, tested by verbal report of the direction of short sequences of coherent dot motion presented within the left hemifield, was preserved. The pattern of cerebral activation elicited by apparent motion stimuli was studied with fMRI and compared to that of normal subjects. In normal subjects, apparent motion stimuli, as compared to darkness, activated strongly striate and extrastriate cortex. When presented to one hemifield only, the contralateral calcarine region was activated while regions on the occipital convexity, including putative area V5, were activated bilaterally. A similar activation pattern was found in the patient with a posterior callosal lesion; unilateral left or right hemifield stimulation was accompanied by activation in the contralateral and ipsilateral occipital convexity. Ipsilateral hemifield representation in the extrastriate visual cortex is believed to depend on callosal input. Our observation suggests that this is not the case for visual motion representation and that other, probably parallel, pathways may mediate visual motion transfer after posterior callosotomy.

Adult↗
PubMed2003

Localization of sucrose synthase and callose in freeze-substituted secondary-wall-stage cotton fibers.

Methods for cryogenic fixation, freeze substitution, and embedding were developed to preserve the cellular structure and protein localization of secondary-wall-stage cotton (Gossypium hirsutum L.) fibers accurately for the first time. Perturbation by specimen handling was minimized by freezing fibers still attached to a seed fragment within 2 min after removal of seeds from a boll still attached to the plant. These methods revealed native ultrastructure, including numerous active Golgi bodies, multivesicular bodies, and proplastids. Immunolocalization in the context of accurate structure was accomplished after freeze substitution in acetone only. Quantitation of immunolabeling identified sucrose synthase both near the cortical microtubules and plasma membrane and in a proximal exoplasmic zone about 0.2 microm thick. Immunolabeling also showed that callose (beta-1,3-glucan) was codistributed with sucrose synthase within this exoplasmic zone. Similar results were obtained from cultured cotton fibers. The distribution of sucrose synthase is consistent with its having a dual role in cellulose and callose synthesis in secondary-wall-stage cotton fibers.

Cell Wall↗
PubMed1975

Structural organization of 'callosal' OBg in human corpus callosum agenesis.

The structural organization of the 'callosal' OBg was studied in Nissl and Weil stained sections of two human brains completely lacking in the corpus callosum. OBg of the normal brain contains a set of distinctive large pyramidal cells in layer III. By contrast, in the brains with absence of the corpus callosum, layer III of OBg contained a slightly reduced number of smaller pyramidal cells than normal, and the characteristic large pyramidal cells were scarsely detectable. Other layers of OBg were not definitely changed. Furthermore, 'acallosal' striate cortex revealed no specific changes. From these observations, it was suggested that the large layer III pyramids of OBg might be closely related to callosal connections.

Agenesis of Corpus Callosum↗
PubMed1982

Divergent strabismus following neonatal callosal section is due to a failure of convergence.

Eye alignment was measured in neonatal callosum-sectioned cats that were 1-3 years old. Alignment was measured from photographs of the cat's corneal reflex when alert, anesthetized and paralyzed, and by plotting to optic disc separation during paralysis. The callosal alignment was equally divergent when alert and paralyzed and was identical to the control alignment under paralysis. Therefore, the alert callosal divergence results from a failure to converge the eyes.

Animals↗
PubMed1983

Widespread callosal connections in infragranular visual cortex of the rat.

Following multiple injections of HRP into the posterior cortex of one hemisphere of adult rats, dense and overlapping distributions of retrogradely labeled cells and anterogradely labeled terminations are observed throughout the depth of the cortex in the region of the border between the lateral portion of area 17 and area 18 in the opposite hemisphere. In contrast to previous studies of the visual callosal pathway, we also find large numbers of labeled callosal cells extending throughout areas 17 and 18 in cortical layers Vc and VIa.

Animals↗
PubMed1984

Columnar organization of callosal and associational projections from rat frontal cortex.

Autoradiography and HRP histochemistry were used to study the laminar and columnar distribution of callosal and associational connections of areas 6 and 10 of Krieg in the rat frontal cortex. In coronal sections through homotopic contralateral areas and ipsilateral somatosensory cortex, terminations of projections arising in frontal cortex formed discrete vertical columns; these were 250-750 micron wide and alternated with unlabeled or poorly labeled areas of approximately equal width. In reconstructions from serial coronal sections through these areas, the terminal fields formed a series of bands. The location of retrogradely labeled neurons tended to reciprocate the distribution of terminal label, although the boundaries of terminal and cell label were not always in precise register. These findings indicate that in the rat, both association and callosal projections exhibit a terminal organization remarkably similar in width and spacing to that observed in primates. Thus, a columnar mode of termination of cortico-cortical fibers may be an organizational feature common to mammalian neocortex.

Animals↗
PubMed1991

The effects of total and partial callosal agenesis on the development of paw preference performance in the BALB/cCF mouse.

The relation between callosal defects and paw preference was investigated in 85 male mice of the BALB/cCF strain. Paw preference was also studied in 30 male Swiss mice. Directional laterality and magnitude of laterality devoid of directionality were evaluated independently. The study of the magnitude of paw preference showed that male BALB/cCF mice were more strongly lateralized than Swiss mice. There was no difference between BALB/cCF mice with callosal defects (abnormal group) and normal BALB/cCF mice. The analysis of directional laterality indicated a population tendency for left-paw use in BALB/cCF as compared to Swiss mice. Furthermore, the percentage of left-pawed animals in the abnormal group (78%) was significantly different from chance level, as opposed to an absence of such differences in the normal BALB/cCF and in Swiss mice. It was concluded that developmental disturbance of the corpus callosum is related to the appearance of a directional populational asymmetry in paw preference.

Agenesis of Corpus Callosum↗