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PubMed2006

Intrahemispheric dysfunction in primary motor cortex without corpus callosum: a transcranial magnetic stimulation study.

BACKGROUND: The two human cerebral hemispheres are continuously interacting, through excitatory and inhibitory influences and one critical structure subserving this interhemispheric balance is the corpus callosum. Interhemispheric neurophysiological abnormalities and intrahemispheric behavioral impairments have been reported in individuals lacking the corpus callosum. The aim of this study was to examine intrahemispheric neurophysiological function in primary motor cortex devoid of callosal projections. METHODS: Intracortical excitatory and inhibitory systems were tested in three individuals with complete agenesis of the corpus callosum and sixteen healthy individuals. These systems were assessed using transcranial magnetic stimulation (TMS) protocols: motor threshold at rest, paired-pulse curve, and cortical silent period. RESULTS: TMS revealed no difference between the patient and control groups on the motor threshold measure, as well as intracortical facilitation and intracortical inhibition systems as tested by paired stimulation. However, intrahemispheric inhibitory function was found to be abnormal in participants without callosal projections, as the cortical silent period duration was significantly increased in the patient group. CONCLUSION: These data suggest that in addition to previously reported impaired interhemispheric function, patients lacking the entire corpus callosum also display abnormal intrahemispheric excitability of the primary motor cortex.

Adult↗
PubMed2000

Normal development of bilateral field advantage and evoked potential interhemispheric transmission time.

Implications of the developmental progression of myelination of the corpus callosum were studied using evoked potential interhemispheric transmission time (EP-IHTT) and the bilateral field advantage (BFA) in letter matching. Forty-two normal children aged 7 to 17 years were asked to respond regarding whether 2 letters matched when presented either unilaterally (both in the same visual field) or bilaterally (1 letter in each field). Evoked potentials were recorded with bilateral midparietal electrodes during unilateral presentations of the letter-matching task. Age-related changes were found for both EP-IHTT and BFA. BFA in reaction time in the visual letter-matching task increased significantly with age. Decreasing EP-IHTT with age was also evident (although only in a statistical trend). These findings lend support to the hypothesis that increased callosal myelination during late childhood has functional significance. Callosal maturation appears to result in faster interhemispheric transfer and increasing ability to integrate information across the midline.

Adolescent↗
PubMed2000

Absence of interhemispheric transfer of unilateral visuomotor learning in young children and individuals with agenesis of the corpus callosum.

This study was undertaken to investigate the role of the corpus callosum in interhemispheric transfer of unilateral visuomotor learning. In the first experiment, the cross-manual performance of 4 callosal agenesis participants was compared to that of 4 age- and IQ-matched controls. In the second experiment, normal children of different ages (6-7 and 11-12 years) and adults were submitted to the same task to assess the impact of callosal maturation on interhemispheric transfer. Participants had to make aiming movements from a starting position toward either a central or a lateral target on the same side as the hand used, while maintaining central fixation. Prior to training, a pretest was performed with the hand contralateral to the hand used during learning. Participants were then submitted to a posttest with the untrained hand. All participants learned the unilateral aiming task in the learning phase, as evidenced by a reduction in spatial errors with an increasing number of practice trials. However, acallosal participants and children aged 6 to 7 years failed to transfer the acquired skill from the trained to the untrained hemisphere. These findings suggest that interhemispheric transfer of visuomotor skills cannot be assumed by other structures in the case of agenesis or morphological immaturity of the corpus callosum. The results further indicate that unilateral visuomotor learning leads to the formation of a single, unihemispheric engram in the absence, whether functional or anatomical, of the corpus callosum.

Adolescent↗
PubMed2003

Normal development of bimanual coordination: visuomotor and interhemispheric contributions.

The corpus callosum is one of the last cortical pathways to develop, continuing to myelinate through the end of the first decade of life. However, the functional consequences of this late development are not entirely known. The importance of callosal development for bimanual motor coordination is suggested by the fact that bimanual coordination in younger children is similar to that of persons with commissurotomy or callosal agenesis. This study focused on the development of bimanual coordination in 67 normally developing children between 6 and 15 years of age using the computerized Bimanual Coordination Test (cBCT). Results indicated that right- and left-hand unimanual motor speed was significantly correlated with age (r = -.26 and -.44, respectively). Age was also significantly associated with accuracy of performance on trials demanding both symmetric (r = -.46) and asymmetric (r = -.50) bi-manual responding. The correlation with asymmetric bimanual responding (requiring greater interhand coordination) remained significant when covarying performance on symmetric response trials. Accuracy on asymmetric bimanual trials requiring greater left- than right-hand speed accounted for the largest portion of this unique, age-related variance. Thus, cBCT performance reveals child development in motor speed and visuomotor processing, as well as the unique contributions of interhemispheric interactions to bimanually coordinated motor activity.

Adolescent↗
PubMed1998

Sulcal variability in the Alzheimer's brain: correlations with cognition.

We mapped the three dimensional (3D) extents and variability of selected sulci in the Alzheimer's brain and explored the relationship between sulcal pattern and patient's cognitive performance. High-resolution MRIs of 10 patients with probable Alzheimer's disease (AD) were linearly transformed into a standard "normalized" 3D atlas (known as the Talairach coordinate system) and, on each relevant slice, contours of the left and right Sylvian fissure, anterior and posterior calcarine, callosal, parietooccipital, and cingulate sulci and the floor of the temporal horn of the lateral ventricle were traced. These landmarks were chosen because of their relative invariant location across individuals and because they demarcate functional boundaries relevant in AD. The sulcal contours were resolved into two-dimensional surfaces that cut through a brain volume. All 10 patients' sulcal surfaces were averaged to determine their mean spatial locations in the Talairach coordinate system. The 3D spatial extents of each patient's sulci were compared with their disease severity based on neuropsychological performance. The 3D sulcal variability, within the "normalized" atlas space, ranged from 4.0 mm for the left callosal sulcus to 9.1 mm for the left Sylvian fissure. Significant correlations were found among the spatial extents for the posterior floor of the right temporal horn of the lateral ventricle (r = -0.89, p < 0.001 for vertical extent) and right anterior calcarine sulcus (r = -0.75, p < 0.01 for anterior-posterior extent) with copying ability of the Rey-Osterrieth Complex Figure; the right anterior calcarine also had a significant relationship (r = -0.72, p = 0.02 for anterior-posterior extent) with performance on the Block Design subtest from the Wechsler Adult Intelligence Scale-Revised. Verbal fluency performance measured by the Controlled Oral Word Association Test was significantly related to the left cingulate (r = 0.91, p < 0.001 for anterior-posterior extent, and r = -0.82, p < 0.01 for vertical extent) and right cingulate (r = -0.72, p < or = 0.02 for vertical extent) sulci. This exploratory study is the first to evaluate the relationship between 3D sulcal variability and cognition; our preliminary findings suggest that the 3D pattern of sulci in the AD brain is related to the severity of the disease as reflected by cognitive performance. In the Talairach brain atlas, sulcal variability, within an AD population, approaches 1 cm. This large variability requires correction when functional imaging data are transformed into the Talairach atlas space to "normalize" individual morphologic differences.

Aged↗
PubMed1979

Traumatic lesions of the corpus callosum.

We investigated the mechanism of damage to the corpus callosum in a study of 46 brains obtained at the autopsies of patients with head injuries. After correlating the gross findings with the site of impact on the head, we think that such lesions in the corpus callosum are caused by stretching of callosal fibers and/or shearing forces in cases in which lateral movement or twisting of the brain occurs. This mechanism of the dynamic development of callosal injuries is also supported by the retraction bulb formation of axons found histologically in the corpus callosum.

Axons↗
PubMed2003

The glial sling is a migratory population of developing neurons.

For two decades the glial sling has been hypothesized to act as a guidance substratum for developing callosal axons. However, neither the cellular nature of the sling nor its guidance properties have ever been clearly identified. Although originally thought to be glioblasts, we show here that the subventricular zone cells forming the sling are in fact neurons. Sling cells label with a number of neuronal markers and display electrophysiological properties characteristic of neurons and not glia. Furthermore, sling cells are continuously generated until early postnatal stages and do not appear to undergo widespread cell death. These data indicate that the sling may be a source of, or migratory pathway for, developing neurons in the rostral forebrain, suggesting additional functions for the sling independent of callosal axon guidance.

Animals↗
PubMed2006

Multiple Eph receptors and B-class ephrins regulate midline crossing of corpus callosum fibers in the developing mouse forebrain.

Agenesis of the corpus callosum (CC) is a rare birth defect that occurs in isolated conditions and in combination with other developmental cerebral abnormalities. Recent identification of families of growth and guidance molecules has generated interest in the mechanisms that regulate callosal growth. One family, ephrins and Eph receptors, has been implicated in mediating midline pathfinding decisions; however, the complexity of these interactions has yet to be unraveled. Our studies shed light on which B-class ephrins and Eph receptors function to regulate CC midline growth and how these molecules interact with important guideposts during development. We show that multiple Eph receptors (B1, B2, B3, and A4) and B-class ephrins (B1, B2, and B3) are present and function in developing forebrain callosal fibers based on both spatial and temporal expression patterns and analysis of gene-targeted knock-out mice. Defects are most pronounced in the combination double knock-out mice, suggesting that compensatory mechanisms exist for several of these family members. Furthermore, these CC defects range from mild hypoplasia to complete agenesis and Probst's bundle formation. Further analysis revealed that Probst's bundle formation may reflect aberrant glial formations and/or altered sensitivity of CC axons to other guidance cues. Our results support a significant role for ephrins and Eph receptors in CC development and may provide insight to possible mechanisms involved in axon midline crossing and human disorder.

Animals↗
PubMed1992

Traumatic callosotomy.

In a 33 years-old epileptic woman with a traumatic impact to the vertex, clinical and radiological studies (skull X-R, CT and MRI) disclosed an extensive callosal section under the topography of the falx, associated to fronto-basal contusions. There was a significant improvement in the epileptic syndrome. No interhemispheric disconnection syndrome could be determined, which is compatible with the posterior regions of the corpus callosum having been spared. This is, to the best of our knowledge, the most extensive callosal injury documented by MRI to date.

Accidental Falls↗
PubMed2001

Two cases of Japanese CADASIL with corpus callosum lesion.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) is a rare hereditary stroke disease. In the present study, a Japanese CADASIL family was first reported with missense mutation of Arg141Cys of Notch3 and a unique lesion of corpus callosum. Upon neuropsychological examination, our case 1 showed only right-handed constructional apraxia associated with corpus callosum lesion. No other callosal disconnection signs were present. Sagittal T2 weighted image of case 1 showed multiple small lesions along with the pericallosal branches from the truncus to the posterior part of the splenium in the corpus callosum. Although detailed mapping of the corpus callosum for functional fractionation in humans remains incomplete, the constructional apraxia on the right may be related to callosal dysfunction from the truncus to the posterior part of the splenium in the corpus callosum.

Corpus Callosum↗
PubMed1993

The Mitchell procedure for the treatment of adolescent hallux valgus. A long-term study.

Thirty patients who had had a total of fifty-one Mitchell procedures to correct adolescent hallux valgus deformities were examined clinically and radiographically an average of seven years (range, three to seventeen years) after the operation. The average age of the patients at the time of the operation was fifteen years (range, ten to nineteen years). The result was excellent in nineteen feet, good in sixteen, fair in six, and poor in ten. The fair and poor results were associated with recurrence of the deformity, stiffness (real or perceived), and unsightly scars. The cause of the fair and poor results was inadequate correction at the time of the operation in six feet and loss of fixation in two; the loss of fixation resulted in one recurrence and one malunion. The remaining eight patients who had a fair or poor result were not totally satisfied and had reservations about more than one of three categories (relief of discomfort, appearance, or range of motion). Seventeen feet had a plantar callosity beneath the second metatarsal head, suggesting increased load-bearing by the second metatarsal. Although sixteen callosities caused no symptoms at the most recent follow-up evaluation, the long-term implications of this altered pattern of weight-bearing are unknown.

Adolescent↗
PubMed1985

Sonographic recognition of agenesis of the corpus callosum.

Agenesis of the corpus callosum may be diagnosed successfully in vivo when sonograms demonstrate absence of corpus callosum; absence of pericallosal and cingulate sulci; "sunburst" pattern of sulci along the medial surface of the hemisphere; wide interhemispheric fissure; elevation of the third ventricle; small, laterally positioned frontal horns with concave medial borders; large, laterally positioned and inverted cingulate gyri; and Probst lateral callosal bundles. Comparison of necropsy specimens with sonograms from eight patients with callosal agenesis illustrates the anatomic basis for these diagnostic features.

Abnormalities, Multiple↗
PubMed1988

MR imaging of the corpus callosum: normal and pathologic findings and correlation with CT.

The MR appearance of the corpus callosum was investigated in 80 normal volunteers. Normal variations in appearance were recorded with regard to age, gender, and handedness. The MR studies of 47 patients with a wide spectrum of callosal disease were also reviewed. Abnormalities included trauma, neoplasia, congenital abnormalities, vascular lesions, and demyelinating and inflammatory conditions. The information provided by MR was compared with that obtained from other radiographic examinations, particularly CT and angiography. In all cases MR provided as much, and frequently more, information than was obtained by other imaging techniques. We believe that MR should be the primary imaging technique for the evaluation of corpus callosal disease.

Adult↗
PubMed2001

Measurement of the corpus callosum using magnetic resonance imaging: analyses of methods and techniques.

Since the first postmortem report of sex-related differences in the size of the human corpus callosum, a number of studies on sex differences have been published, but results conflicted. The aim of this review was not to assess the possible existence and magnitude of sex variations in the size of the corpus callosum but to analyze methodological differences in several studies using Magnetic Resonance Imaging to investigate the sexual dimorphism in the size of the corpus callosum. Methodological problems arise at several steps of the method: sampling, imagery techniques, and measurements. Moreover, the means of callosal areas obtained by the nine reported studies are significantly different. The hypothesis that methodoiogical differences could explain these differences is supported by statistical results. A common method for investigating sex-related differences in callosal morphology appears necessary to resolve the question of a real sexual dimorphism of the corpus callosum and its subregions.

Corpus Callosum↗
PubMed1987

The deafferented visual cortex: neuronal activity and visual evoked potentials.

The callosal transfer of information to the visual cortex following its unilateral deafferentation from its geniculate input was studied in both hemispheres. Deafferentation was performed in adult cats by sectioning the optic tract. Action potentials of single cortical cells and visual evoked potentials were recorded from area 17-18 boundary in acute and chronic operated cats. In the deafferented hemisphere, cortical cells were usually visually inactive. However, some recovery of function took place in this hemisphere in the chronic cats, as expressed by the increase in the proportion of S-cells. In the intact hemisphere diminution of responsiveness and reduction of selectivity to the stimulus orientation and direction were found. The responsiveness and selectivity level in the intact hemisphere increased with postoperative time. The ocular dominance distribution in this hemisphere was similar to that of our normal control cats. The characteristics of the visual evoked potentials were in keeping with the hemispheric dominance of the cortical cells found in the experimental cats. It was concluded that a plasticity related mechanism is involved in the recovery of callosal activation of visual cortical cells following deafferentation.

Animals↗
PubMed1988

Neural net simulation of the corpus callosum.

The effects of simulated anatomical and physiological parameters were investigated in a "neural net" model, where two neural nets corresponding to two small patches of cerebral cortex were connected by a simulated "corpus callosum." The isolated neural nets have previously been shown to exhibit oscillatory activity similar to the raw EEG. By connecting the nets with fibers which have a specified percentage of inhibition and a specified percentage of homotopicity, the effects of such parameters on the cyclic activity of the nets were studied. It was found that, regardless of the inhibitory-excitatory nature of the simulated corpus callosum, the cyclic activity established in one hemisphere is more readily transferred to the contralateral hemisphere, the greater the percentage of homotopic callosal fibers. Learning was more rapid when the effect of the corpus callosum was primarily excitatory, but learning also took place over inhibitory or mixed callosal tracts. The simulation does not therefore resolve the issue of the predominant physiological effect of the corpus callosum, but does indicate that, given the assumptions of the simulation, "learning" can occur regardless of the percentage of excitatory or inhibitory fibers. It is noteworthy that homotopicity was more important for learning across an inhibitory tract than across an excitatory tract.

Animals↗
PubMed1991

A rapid method for macerating phloem.

Sieve cells and sieve tube members can be macerated from the phloem of various organs of woody and herbaceous species by autoclaving the tissue in a mild macerating medium. This treatment does not digest the primary walls or the callose deposits on the sieve areas and sieve plates of the sieve elements. These cells can then be recognized by the fluorescence of their callose after staining with aniline blue. Sometimes adjacent sieve elements fail to separate and one can observe details of their junctures.

Cytological Techniques↗
PubMed2001

Cow- and quarter-level risk factors for Streptococcus uberis and Staphylococcus aureus mastitis.

This study was designed to identify risk factors for intramammary infections with Streptococcus uberis and Staphylococcus aureus under field conditions. An 18-mo survey with sampling of all quarters of all lactating cows at 3-wk intervals was carried out in three Dutch dairy herds with medium bulk milk somatic cell count (200,000 to 300,000 cells/ml). Quarter milk samples were used for bacteriology and somatic cell counting. Data on parity, lactation stage, and bovine herpesvirus 4-serology were recorded for each animal. During the last year of the study, body condition score, and teat-end callosity scores were recorded at 3-wk intervals. A total of 93 new infections with Strep. uberis were detected in 22,665 observations on quarters at risk for Strep. uberis infection, and 100 new infections with Staph. aureus were detected in 22,593 observations on quarters at risk for Staph. aureus infection. Multivariable Poisson regression analysis with clustering at herd and cow level was used to identify risk factors for infection. Rate of infection with Strep. uberis was lower in first- and second-parity cows than in older cows, and depended on stage of lactation in one herd. Quarters that were infected with Arcanobacterium pyogenes or enterococci, quarters that had recovered from Strep. uberis- or Staph. aureus-infection in the past, and quarters that were exposed to another Strep. uberis infected quarter in the same cow had a higher rate of Strep. uberis infection. Teat-end callosity and infection with coagulase-negative staphylococci or corynebacteria were not significant as risk factors. Rate of Staph. aureus infection was higher in bovine herpesvirus 4-seropositive cows, in right quarters, in quarters that had recovered from Staph. aureus or Strep. uberis infection, in quarters exposed to other Staph. aureus infected quarters in the same cow, and in quarters with extremely callused teat ends. Infection with coagulase-negative staphylococci was not significant as a risk factor. The effect of infection with corynebacteria on rate of infection with Staph. aureus depended on herd, stage of lactation, and teat-end roughness. Herd level prevalence of Strep. uberis or Staph. aureus, and low quarter milk somatic cell count were not associated with an increased rate of infection for Strep. uberis or Staph. aureus.

Animals↗