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PubMed1992

The topography of callosal reading pathways. A case-control analysis.

Lesion topography and reading ability were analysed in 17 patients with dominant posterior cerebral artery territory infarction. Patients with dominant posterior cerebral artery infarction in whom reading was unaffected served as an anatomical control group. Normal readers had lesions in the medial and ventral occipital lobe, sparing dorsal white matter pathways and the ventral temporal lobe. Global and permanent alexia occurred only with additional injury to the splenium, forceps major or white matter above the occipital horn of the lateral ventricle. These data suggest that callosal pathways mediating reading lie above the occipital horn and have little connection with the ventromedial occipital region. Patients with 'spelling dyslexia' had large lesions of the ventral temporal lobe involving cortical regions believed to participate in later stages of visual processing. These findings provide a framework for the prediction of dyslexia type and severity based on lesion topography.

Adult↗
PubMed2005

Corpus callosal microstructural integrity influences interhemispheric processing: a diffusion tensor imaging study.

Normal aging and chronic alcoholism result in disruption of brain white matter microstructure that does not typically cause complete lesions but may underlie degradation of functions requiring interhemispheric information transfer. We examined whether the microstructural integrity of the corpus callosum assessed with diffusion tensor imaging (DTI) would relate to interhemispheric processing speed. DTI yields estimates of fractional anisotropy (FA), a measure of orientation and intravoxel coherence of water diffusion usually in white matter fibers, and diffusivity ( ), a measure of the amount of intracellular and extracellular fluid diffusion. We tested the hypothesis that FA and would be correlated with (i) the crossed-uncrossed difference (CUD), testing visuomotor interhemispheric transfer; and (ii) the redundant targets effect (RTE), testing parallel processing of visual information presented to each cerebral hemisphere. FA was lower and higher in alcoholics than in controls. In controls but not alcoholics, large CUDs correlated with low FA and high in total corpus callosum and regionally in the genu and splenium. In alcoholics but not controls, small RTEs, elicited with equiluminant stimuli, correlated with low FA in genu and splenium and high in the callosal body. The results provide in vivo evidence for disruption of corpus callosum microstructure in normal aging and alcoholism that has functional ramifications for efficiency in interhemispheric processing.

Aging↗
PubMed2003

TIP, a novel host factor linking callose degradation with the cell-to-cell movement of Potato virus X.

The cell-to-cell movement of Potato virus X (PVX) requires four virus-encoded proteins, the triple gene block (TGB) proteins (TGB25K, TGB12K, and TGB8K) and the coat protein. TGB12K increases the plasmodesmal size exclusion limit (SEL) and may, therefore, interact directly with components of the cell wall or with plant proteins associated with bringing about this change. A yeast two-hybrid screen using TGB12K as bait identified three TGB12K-interacting proteins (TIP1, TIP2, and TIP3). All three TIPs interacted specifically with TGB12K but not with TGB25K or TGB8K. Similarly, all three TIPs interacted with beta-1,3-glucanase, the enzyme that may regulate plasmodesmal SEL through callose degradation. Sequence analyses revealed that the TIPs encode very similar proteins and that TIP1 corresponds to the tobacco ankyrin repeat-containing protein HBP1. A TIP1::GFP fusion protein localized to the cytoplasm. Coexpression of this fusion protein with TGB12K induced cellular changes manifested as deposits of additional cytoplasm at the cell periphery. This work reports a direct link between a viral movement protein required to increase plasmodesmal SEL and a host factor that has been implicated as a key regulator of plasmodesmal SEL. We propose that the TIPs are susceptibility factors that modulate the plasmodesmal SEL.

Amino Acid Sequence↗
PubMed2006

Nonprogressive transgene-related callosal and hippocampal changes in PDAPP mice.

We have previously shown that homozygous PDAPP mice, a transgenic model of Alzheimer's-like amyloidosis, have abnormal corpus callosi and anterior hippocampi. Now, we investigated the extent to which these morphological abnormalities are correlated with mutant gene dose in a larger, independent, and substantially younger cohort. Homozygous and heterozygous PDAPP mice had significantly smaller callosal commissure length and anterior hippocampal area than controls. Reductions correlated with mutant APP gene dose, with homozygotes showing the greatest reduction, and were present at 2 months of age. These findings and previous work with APP knockouts suggest that PDAPP mice have impaired white matter development due to interference with native murine APP.

Agenesis of Corpus Callosum↗
PubMed2000

Bilateral receptive field neurons and callosal connections in the somatosensory cortex.

Earlier studies recording single neuronal activity with bilateral receptive fields in the primary somatosensory cortex of monkeys and cats agreed that the bilateral receptive fields were related exclusively to the body midline and that the ipsilateral information reaches the cortex via callosal connections since they are dense in the cortical region representing the midline structures of the body while practically absent in the regions representing the distal extremities. We recently found a substantial number of neurons with bilateral receptive fields on hand digits, shoulders-arms or legs-feet in the caudalmost part (areas 2 and 5) of the postcentral gyrus in awake Japanese monkeys (Macaca fuscata). I review these results, discuss the functional implications of this bilateral representation in the postcentral somatosensory cortex from a behavioural standpoint and give a new interpretation to the midline fusion theory.

Animals↗
PubMed1992

Inhibition and Ultraviolet-Induced Chemical Modification of UDP-Glucose:(1,3)-beta-Glucan (Callose) Synthase by Chlorpromazine : Mechanism of Chlorpromazine Binding to the Plant Plasma Membrane.

UDP-glucose:(1,3)-beta-glucan (callose) synthase (CS) from storage tissue of red beet (Beta vulgaris L.) was strongly inhibited by the phenothiazine drug chlorpromazine (CPZ). In the absence of ultraviolet irradiation, CPZ was a noncompetitive inhibitor with 50% inhibitory concentration values for plasma membrane and solubilized CS of 100 and 90 mum, respectively. Both the Ca(2+)- and Mg(2+)- stimulated components of CS activity were affected. CPZ inhibition was partially alleviated at saturating levels of Ca(2+), but not Mg(2+), suggesting that CPZ interferes with the Ca(2+)-binding site of CS. Binding experiments with [(14)C]CPZ, however, showed strong non-specific partitioning of CPZ into the plasma membrane, providing evidence that perturbation of the membrane environment is probably the predominant mode of inhibition. Ultraviolet irradiation at 254 nm markedly enhanced CPZ inhibition, with complete activity loss following exposure to 4 mum CPZ for 2 min. Inhibition followed a pseudo-first order mechanism with at least three CPZ binding sites per CS complex. Under these conditions, [(3)H]CPZ was covalently incorporated into plasma membrane preparations by a free radical mechanism; however, polypeptide labeling profiles showed labeling to be largely nonspecific, with many polypeptides labeled even at [(3)H]CPZ levels as low as 1 mum, and with boiled membranes. Although CPZ is one of the most potent known inhibitors of CS, its use as a photolabel will require a homogeneous CS complex or establishment of conditions that protect against the interaction of CPZ with specific binding sites located on various polypeptide components of the CS complex.

Journal Article↗
PubMed2005

Callosal bisection and transcallosal secondary antiepileptogenesis.

More than 28,000 neuroscientists and 3,000 epileptologists gathered at their respective 2001 meetings of the Society for Neuroscience and the American Epilepsy Society. Yet only six articles, one directly and five indirectly, discussed the corpus callosum (CC). Is not this in itself a remarkable finding? Are there no mysteries left? The reality is that considerable uncertainties exist regarding the rationale for callosal bisection (CCB) that causes contrasting effects (i.e., amelioration of generalized seizure, at times leading to freedom from seizure, and intensification of postoperatively fragmented seizure, at times leading to status epilepticus). Similarly, the clinical relevance of EEG mirror focus formation, an experimentally well-established transcallosal consequence of partial cortical epileptogenesis, continues to be debated. This presentation revisits these unresolved issues (a) to gain insight into the dynamic role played by the CC in medically refractory epilepsy, and (b) to promote the development of antiepileptogenic tools that are currently unavailable.

Animals↗
PubMed2004

Stage-specific and opposing roles of BDNF, NT-3 and bFGF in differentiation of purified callosal projection neurons toward cellular repair of complex circuitry.

Cellular repair of neuronal circuitry affected by neurodegenerative disease or injury may be approached in the adult neocortex via transplantation of neural precursors ("neural stem cells") or via molecular manipulation and recruitment of new neurons from endogenous precursors in situ. A major challenge for potential future approaches to neuronal replacement will be to specifically direct and control progressive differentiation, axonal projection and connectivity of neural precursors along a specific neuronal lineage. This goal will require a progressively more detailed understanding of the molecular controls over morphologic differentiation of specific neuronal lineages, including neurite outgrowth and elongation, in order to accurately permit and direct proper neuronal integration and connectivity. Here, we investigate controls over the morphologic differentiation of a specific prototypical lineage of cortical neurons: callosal projection neurons (CPN). We highly enriched CPN to an essentially pure population, and cultured them at three distinct stages of development from embryonic and postnatal mouse cortex by retrograde fluorescence labelling, followed by fluorescence-activated cell sorting. We find that specific peptide growth factors exert direct stage-specific positive and negative effects over the morphologic differentiation and process outgrowth of CPN. These effects are distinct from the effects of these growth factors on CPN survival [Catapano et al. (2001)J. Neurosci., 21, 8863-8872]. These data may be critical for the future goal of directing lineage-specific neuronal differentiation of transplanted or endogenous precursors/"stem cells" toward cellular repair of complex cortical circuitry.

Aging↗
PubMed2005

Regional differences in NREM sleep slow-wave activity in mice with congenital callosal dysgenesis.

Topographic differences in the sleep EEG have been repeatedly found in humans and rodents. A frontal predominance of EEG slow-wave activity (0.75-4 Hz; delta band) during non-rapid eye movement (NREM) sleep is particularly evident under conditions of increased sleep propensity. Local aspects of neuronal connectivity in the neocortex that are modified by specific neuronal stimulation may underlie these differences. To investigate the role of altered neuronal connectivity on anterior-posterior EEG topography, sleep was recorded in mice with congenital dysgenesis of the corpus callosum (B1 strain) during baseline and after 6 h sleep deprivation (SD). In these mice neuronal connections within a hemisphere are increased due to the longitudinal Probst bundle, a structure of re-routed callosal fibers. After SD the frequencies above 1.5 Hz within the delta band in NREM sleep were reduced in B1 mice compared with control C57BL/6 mice, a strain that has a normal corpus callosum, while power in the lowest frequency band (0.75-1.0 Hz) was enhanced in B1 mice. The differences between the strains subsided in the course of recovery. The redistribution of EEG power within the delta band in the frontal region in mice with a well developed Probst bundle, suggests a role of intracortical connectivity in local sleep regulation.

Agenesis of Corpus Callosum↗
PubMed2005

Callosal anomalies with interhemispheric cyst: expanding the phenotype.

AIM: To determine the frequency and clinical features of corpus callosum hypoagenesis, dysgenesis or hypoplasia in conjunction with extraparenchymal interhemispheric cyst. METHODS: A retrospective study of clinical files and imaging records of all 2500 children referred to the University Department of Paediatrics, Catania, Italy, who underwent neuroimaging by ultrasound, computerized tomography or magnetic resonance imaging in 1992-2003. Five children (all girls, aged 2-18 y) were found to have abnormalities of the corpus callosum associated with interhemispheric cyst. RESULTS: Three cases were type 2b, one type 2c and one mixed type 2b and 2c according to the classification proposed by Barkovich et al. The onset of clinical symptoms was very early, with severe neurological involvement, seizures that were difficult to treat and profound psychomotor retardation. CONCLUSIONS: In callosal anomalies with cysts, a prevalence in females is not confined to type 2b cysts, the spectrum of abnormalities of the corpus callosum is more varied than previously recorded, and the natural history and outcome of the condition are poor with profound developmental delay and drug-resistant seizures. The finding that all the cases were of type 2 suggests that the overall phenotype is more widespread than previously thought and may present in association with other complex syndromes.

Age Distribution↗
PubMed1981

Cognitive interaction after staged callosal section: evidence for transfer of semantic activation.

Sensory and cognitive functions were assessed in a right-handed male before and after partial and complete callosal commissurotomy. After the initial posterior section was made, there was no evidence of interhemispheric sensory transfer, although the left hemisphere did have access to stimulus-related semantic and episodic information from the right hemisphere. After the callosum was completely sectioned, this exchange was no longer observed.

Adult↗
PubMed1980

Posterior callosal section in a non-epileptic patient.

The major studies of the effects of callosal section in humans have been conducted in severe epileptic patients in whom commissurotomy has been performed for management of intractable seizures. In spite of the evidence which has been amassed it is possible to criticise the results, on the grounds that all patients had seizures for many years prior to surgery and hence it is conceivable that some adaptive reorganisation of the epileptic brain might account for the different behaviour of the two hemispheres. Specifically, since the primary epileptic focus and its possible underlying focal damage are often asymmetric, one hemisphere might have had to adapt to the functional deficit of the other and thereby produce the basis for the unusually striking hemispheric differences. The answer to these reservations must come from the study of non-epileptic subjects who undergo some form of commissurotomy for reasons other than treatment of seizures, particularly if the intervention involves the posterior third of the corpus callosum, the sector considered responsible for the more remarkable "disconnection" signs. Only seven such cases have been reported. Here we report findings in a non-epileptic and previously normal 16-year-old boy who underwent section of the splenium for exploration of a pineal tumour. Our results indicate that surgical section of the splenium produced visual disconnection signs comparable to those seen in epileptic patients with complete commissurotomy.

Adolescent↗
PubMed2000

Conduction deficits of callosal fibres in early multiple sclerosis.

OBJECTIVE: To study the diagnostic usefulness of transcallosal inhibition (TI) elicited by transcranial magnetic stimulation (TMS) in detecting central conduction deficits in early multiple sclerosis. Corticospinally mediated excitatory responses evoked by TMS are accepted as a sensitive diagnostic tool in multiple sclerosis. Recently, TI evoked by TMS has been introduced as a new paradigm to test the function of callosal fibres interconnecting both hand associated motor cortices. METHODS: Focal TMS of the motor cortex was performed in 50 patients with early relapsing-remitting multiple sclerosis. Corticospinally mediated (central motor latencies, amplitudes) and transcallosally mediated (onset latency and duration of TI) stimulation effects were investigated. RESULTS: TMS disclosed abnormalities of corticospinally mediated responses in 62% and of TI in 80% of the patients. CONCLUSION: The assessment of TI allows the discovery of lesions within the periventricular white matter that were not accessible by neurophysiological techniques before. This new paradigm increases the sensitivity of TMS with which to detect central conduction deficits in early multiple sclerosis.

Adolescent↗
PubMed1992

Use of the callosal grid system for the preoperative identification of the central sulcus.

The callosal grid system based on modern imaging techniques facilitates the identification of the central sulcus by its relationship to the midcallosal plane. Imaging with or without the stereotactic frame allows precise localization of various anatomic sites, which can be compartmentalized within subdivisions of the grid system. The information gained permits accurate preoperative planning and intraoperative recognition of the central sulcus and adjacent neurovascular structures.

Brain↗
PubMed1994

Right unilateral agraphia following callosal infarction in a left-hander.

A left-handed Japanese man is reported who presented right-hand agraphia and tactile anomia following callosal infarction. Magnetic resonance imaging revealed an ischemic lesion extending from the posterior half of the trunk to the splenium of the corpus callosum. In his right handwriting, the 'Kana' (phonogram) was more severely impaired than the 'Kanji' (ideogram), and the most frequent typewriting error was morphological followed by neographism. His visuoconstructional ability was also more impaired in the right hand than in the left. Right-hand agraphia in our case is readily explained by the right hemisphere dominance both for language and visuoconstructional ability.

Agraphia↗
PubMed2002

White-matter alterations and callosal abnormalities in syndromic patients with mental retardation.

The aim of this study was to evaluate the frequency of callosal abnormalities and white matter alterations in syndromic patients. The authors report on the cerebral magnetic resonance imaging (MRI) morphologic analysis of the corpus callosum and white matter in 73 normal subjects and 61 syndromic patients. The study of the corpus callosum was carried out by MRI using different morphometric methods: measurement of the dimensions of length and thickness of genu, body, and splenium; measurement of angles obtained using the sagittal plane; and application of the proportional grid of Talairach. The evaluation of the white matter was carried out by applying a subjective grading scale. Abnormalities of the corpus callosum were found in about 50% of the syndromic subjects; in half of these cases, the abnormalities were associated with white matter alterations. In five syndromic patients (8.2%), the white matter alterations were not associated with corpus callosum abnormalities. This study shows that corpus callosum abnormalities are frequent in syndromology regardless of the syndrome type.

Adolescent↗
PubMed2001

Callosal contribution to procedural learning in children.

A previous study in acallosal patients (De Guise, et al., 1999) has demonstrated the crucial role of the corpus callosum (CC) in a procedural learning task that requires the participation of both hemispheres. Because children often display limitations in interhemispheric communication linked to callosal immaturity, we expected that they would have difficulties learning a procedural skill that involved interhemispheric integration during its acquisition, but not when the skill was learned intrahemispherically. To test this hypothesis, 40 children, divided into 4 age groups (6 to 8 years, 9 to 11 years, 12 to 14 years, and 15 to 16 years), performed a modified version of the serial reaction time task developed by Nissen and Bullemer (1987). This task involves uni- or bimanual key-pressing responses to a fixed sequence of 10 visual stimuli that are repeated 80 times. All the children were able to learn the visuomotor skill in the unimanual condition and to transfer it interhemispherically. However, only the older children (12 years and over) learned the task in the bimanual (interhemispheric) condition. The results indicate that the maturation of the CC affects interhemispheric acquisition of a procedural skill in two different ways: While the immature CC appears to be sufficient to transfer a skill acquired by one hemisphere, a mature CC seems to be required to learn the skill bihemispherically. The latter skill was achieved around the age of 12, coinciding with the end of the maturation cycle of the CC. Although the young children were unable to learn the bimanual task implicitly, some of them showed explicit knowledge of the procedure, confirming once again the dissociation between explicit and implicit memory suggested by Squire (1992).

Adolescent↗
PubMed1988

Localization of callosal auditory pathways: a CT case study.

The position of the auditory pathways in the human corpus callosum has not been defined by modern imaging techniques. We report a case with a discrete hemorrhagic lesion in the posterior body of the corpus callosum. The only signs of disturbed callosal function were limited to the auditory system--suppression of left ear stimuli with dichotic listening and neglect of left-sided auditory simultaneous stimuli.

Adult↗