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PubMed1983

Spatial dissociation of visual inputs alters the origin of the corpus callosum.

The distribution of the origin of corpus callosum neurons was investigated in cats reared with an optically induced strabismus by applying horseradish peroxidase (HRP) to severed callosal axons. These animals demonstrated an enlargement of the region of callosal connectivity compared to normal cats. Bilaterally there was an expanded efferent zone, with callosal cell bodies widely distributed in area 17, extending down the medial bank of the lateral gyrus halfway to the fundus of the splenial sulcus. This suggests that rearing a cat with visual spatial dissociation requires additional communication between the hemispheres in the form of increased callosal connections between cortical regions representing more peripheral portions of the visual field.

Animals↗
PubMed1988

Norepinephrine is a presynaptic input to visual corpus callosum cells.

The neurochemical identity of presynaptic inputs to cell bodies of corpus callosum fibers (callosal cells) located in visual cortex of the cat was investigated using a double labeling technique. Callosal cells were labeled by horseradish peroxidase applied to the severed ends of callosal fibers, and [3H]norepinephrine (NE) was injected into the crown of the lateral gyrus corresponding to the visual cortical area 17/18 border to label synapses. The tissue surrounding the injection sites was processed for electron microscope autoradiography. The results show that NE can be localized to cortical synapses contacting callosal cells in visual cortex of the cat.

Animals↗
PubMed1991

Cortical cells' physiology following visual split brain in developing cats.

We have studied physiologically whether visual cortex cells in areas 17 and 18 of split-brain cats preserve their performance despite the blockage of both binocularity and of interhemispheric communication. The absolute majority of the cells in cats underwent split-brain surgery as kittens and adults and were driven by the ipsilateral eye, resulting in the absence of interhemispheric interaction. Similar results were found in cats and kittens that underwent only chiasm split surgery, although some recovery of callosal transfer was found in the latter. A remarkable loss of binocularity was found when only callosal transection was performed, both in adult cats and in kittens, although some ipsilateral eye dominance was observed in the latter. As to the deprived cats, while in the inexperienced hemisphere (ipsilateral to the deprived eye), the majority of the cells was visually unresponsive, in the contralateral (experienced) hemisphere, the majority was responsive. A considerable reduction in responsiveness was found in the callosally transected cats and kittens. Generally, a degradation of function was found in the various properties as a result of chiasmal and/or callosal transection. The main effect is the increased number of cells with diffuse and incomplete receptive fields. There was also a reduction in the proportion of orientation-selective cells, mainly in the split-brain cats. It was concluded that, despite the high amount of hemispheric independency in the normal brain, the integrity and simultaneous action of the two hemispheres are needed for the normal functioning of visual cortex cells.

Aging↗
PubMed2006

Mapping corpus callosum deficits in autism: an index of aberrant cortical connectivity.

BACKGROUND: Volumetric studies have reported reductions in the size of the corpus callosum (CC) in autism, but the callosal regions contributing to this deficit have differed among studies. In this study, a computational method was used to detect and map the spatial pattern of CC abnormalities in male patients with autism. METHODS: Twenty-four boys with autism (aged 10.0 +/- 3.3 years) and 26 control boys (aged 11.0 +/- 2.5 years) underwent a magnetic resonance imaging (MRI) scan at 3 Tesla. Total and regional areas of the CC were determined using traditional morphometric methods. Three-dimensional (3D) surface models of the CC were also created from the MRI scans. Statistical maps were created to visualize morphologic variability of the CC and to localize regions of callosal thinning in autism. RESULTS: Traditional morphometric methods detected a significant reduction in the total callosal area and in the anterior third of the CC in patients with autism; however, 3D maps revealed significant reductions in both the splenium and genu of the CC in patients. CONCLUSIONS: Statistical maps of the CC revealed callosal deficits in autism with greater precision than traditional morphometric methods. These abnormalities suggest aberrant connections between cortical regions, which is consistent with the hypothesis of abnormal cortical connectivity in autism.

Adolescent↗
PubMed2004

Effects of handedness and gender on macro- and microstructure of the corpus callosum and its subregions: a combined high-resolution and diffusion-tensor MRI study.

The corpus callosum (CC) represents the major commissural tract connecting the two cerebral hemispheres and is supposed to play crucial integrative role in functional hemispheric specialization. The present study examined whether interindividual variations in macro- and microstructure of the human CC are associated with handedness and gender. Therefore, a combined diffusion-tensor (DTI) and high-resolution morphological MRI study was performed on 34 right- and 33 left-handed subjects of both sexes. The mid-sagittal surface areas and quantitative measures of molecular diffusion (relative anisotropy, mean diffusion) of the total CC and its subregions (genu, truncus, posterior third) were determined. Analysis revealed a larger total callosal area in right- as compared to left-handed subjects and in males as compared to females. Throughout all callosal subregions, anisotropy was found to be increased in left-handed as well as in male subjects, while the mean diffusion was diminished only in left-handers. For the posterior third of the CC, a significant negative correlation (r=-0.34) between anisotropy and area was detected in right-handed subjects. Summarized, significant alterations in the molecular diffusion and in the size of the CC with respect to gender and handedness were revealed in the present study. These findings can be interpreted as handedness- and gender-related differences in macro- and microstructure of the callosal pathways. It was demonstrated that the inspection of the callosal microstructure using DTI yields empirical evidence on interhemispheric connectivity that goes well beyond the information revealed by anatomical measurements alone. Thus, DTI has proven to be a useful additional method in cognitive neuroscience.

Adult↗
PubMed2005

Dysmorphology and microstructural degradation of the corpus callosum: Interaction of age and alcoholism.

Chronic alcohol abuse is a ubiquitous health and societal problem, with a growing prevalence in the older population. Alcoholism is a source of substantial deterioration in brain tissue and has been consistently observed in vivo and postmortem in white matter. To quantify the potential compounded effect of age and alcoholism, we used conventional structural MRI and diffusion tensor imaging (DTI) to examine the macrostructural and microstructural integrity of the corpus callosum, one of the most prominent white matter structures of the brain, in 131 adults, age 27-75 years. Compared with the 74 controls, the 40 alcoholic men and 17 alcoholic women, who were abstinent from alcohol for an average of 3 months, showed similar patterns and extents of callosal shrinkage, which was greatest in the genu and body and less prominent in the splenium. Microstructural integrity was measured with DTI as fractional anisotropy, an index of intravoxel orientational coherence of white matter fibers, and bulk mean diffusivity, an index of the amount of intravoxel water motility. The macrostructural shrinkage was accompanied by abnormalities in anisotropy and diffusivity of the microstructural environment of these callosal regions, indicative of disruption of structural constituents of local brain white matter. Correlational analyses revealed an age-alcohol interaction, where older alcoholics had smaller genu and splenium and higher diffusivity in these regions than younger alcoholics. Significant correlations between regional MRI and DTI measures and performance on working memory, visuospatial ability, and gait and balance provided evidence for the functional ramifications of the callosal abnormalities in the alcoholics. Thus, despite abstinence from alcohol, the interaction of age and recent alcoholism history exerted a compounded untoward effect on callosal macrostructure and microstructure.

Adult↗
PubMed1998

Interhemispheric transfer in normals and acallosals: latency adjusted evoked potential averaging.

Interhemispheric transfer time (IHTT) can be estimated from visual evoked potentials (EPs). Latency adjusted averaging (LAA) produces EPs which have enhanced components. LAA also provides estimates of EP latency variance and signal-to-noise ratio (S/N). LAA was tested in analysis of EP-IHTT in normal and acallosal subjects. It was hypothesized that in normals S/N and latency variance would reveal signal degradation resulting from interhemispheric transfer. LAA in normals replicated IHTT findings for both P1 and N1 latency. Latency variance did not increase for cross-callosal measures, whereas the S/N measure showed significant EP degradation due to callosal transfer. EPs from five subjects with callosal absence (two commissurotomy; two complete and one partial callosal agenesis) showed significantly larger than normal latency variability, as well as decreased S/N ratios, for cross-hemisphere visual EPs. Results support the value of LAA in EP research on adequacy of hemispheric interactions in clinical populations.

Adolescent↗
PubMed2002

The effect of corpus callosum agenesis on neocortical thickness and neuronal density of BALB/cCF mice.

We used acallosal and normal adult BALB/cCF mice to test the hypothesis that the development of the corpus callosum is relevant for the establishment of a normal structure of the neocortex. Neuronal density and thickness of individual layers were analyzed in neocortical regions with abundant callosal connections (area 6 and the 17/18a border) and in the relatively acallosal area 17. In area 6, acallosal mice exhibited a total neocortical thickness smaller than that of normal mice, as well as thinner layers II+III and IV. Similar data were obtained at the 17/18a border, where the total thickness of the cortex and of layers II+III was smaller in the acallosal mice than in normal ones. In contrast, no significant thickness differences were documented in area 17 of acallosal versus normal mice. The quantitative data obtained in the analyzed neocortical regions did not show differences in neuronal density between acallosal and normal mice. The reduced cortical thickness, associated with the comparatively normal neuronal density in neocortical regions which normally have abundant callosal connections, provides indirect indication of a reduction in the number of cortical neurons in acallosal mice. This assumption was also supported by the lack of evidence of neocortical alterations in the acallosal area 17. The present findings suggest that during development neocortical neurons destined to receive a massive callosal input may die as a result of lack of afferents. Altogether the present data indicate that the input provided by callosal axons is necessary for a normal development of the neocortex.

Afferent Pathways↗
PubMedDate not supplied

Post-tetanic modification of the efficiency of excitatory transmission in neural networks including interhemispheric connections.

This is the first report of modifiable reciprocal transcallosal monosynaptic excitatory connections, detected in in vivo experiments in the rat motor cortex by recording of multineuron activity and cross-correlation analysis. High-frequency microstimulation of a small group of cortical neurons in one hemisphere was shown to alter the efficiency of transcallosal excitatory connections, and also altered the efficiency of ipsilateral connections in both hemispheres. Post-tetanic changes consisted of long-term potentiation and depression. Neurons producing spike trains were found to have better conditions (compared with other neurons) for long-term potentiation of inputs converging on them. Synapses formed by axon collaterals of a given callosal cell on several neurons could simultaneously induce both long-term potentiation and long-term depression, while a given callosal neuron could simultaneously show long-term potentiation in some synapses and long-term depression in others. After microstimulation there were increases in the number of background-active callosal neurons, along with increases in the number and efficiency of transcallosal connections, while the number and efficiency of ipsilateral connections decreased. These data lead to the conclusion that ipsilateral inhibition is more effective than transcallosal inhibition. Microstimulation modified the pattern of initially existing connections between the many elements of ensembles including callosal cells in both hemispheres.

Action Potentials↗
PubMed1989

Maturation and connectivity of the visual cortex in monkey is altered by prenatal removal of retinal input.

In several species, the peripheral input from the eyes partly determines the pattern of interconnections between the visual areas of the two cerebral hemispheres through the fibre tract termed the corpus callosum. In the macaque monkey, the neurons projecting through the callosum are largely restricted to area 18 throughout ontogeny, whereas area 17 is characterized by few or no callosal projections. Here, we show that suppressing the peripheral input by prenatal removal of the eyes leads to a marked reduction in the extent of area 17, resulting in a large shift in the position of the histologically identifiable boundary between the two areas. Even so, the boundary continues to separate an area rich with callosal connections (area 18) from one poor in such projections (area 17), indicating there is no effect on the callosal connectivity of area 17. In contrast, in area 18, eye removal results in many more neurons with callosal projections than in normal animals. The results suggest that the factors that determine the parcellation of cortical areas also specify their connectivity.

Animals↗
PubMed2005

Pollen-wall formation in Arum alpinum.

BACKGROUND AND AIMS: Arum alpinum has a quite uncommon pollen wall. A sporopolleninous ektexine is missing. The outermost pollen wall layer is formed by the endexine which is covered by polysaccharidic ornamentation elements. An ontogenetical investigation was accomplished to clarify pollen-wall development, with special reference to callose and pollen-wall development. METHODS: Plants of Arum alpinum grown in their natural habitat were collected once a week within the vegetative period and processed for semi- and ultra-thin sectioning. KEY RESULTS: At any stage of pollen-wall formation callose is missing. Microspores are released from the tetrad by invagination of the amoeboid tapetum. The polysaccharidic wall ornamentations are formed by the tapetum. CONCLUSIONS: There appears to be no truth in the dogma that callose is essential for microspore separation and release from the tetrad. The lack of callose does not influence fertility but could be the reason for the uncommon pollen wall, where a sporopolleninous ektexine is missing.

Arum↗
PubMed2000

Parallel visuomotor processing in the split brain: cortico-subcortical interactions.

We tested nine patients with callosal pathology in a simple reaction time task with and without redundant targets in the same or opposite visual hemifield. Four patients showed large facilitation (redundancy gain) in the presence of a redundant target, exceeding probability summation models (neural summation). Five patients showed redundancy gain not exceeding probability models. Violation of probability models was not associated with a specific type of callosal lesion. Neural summation, which probably occurs at collicular level, may be modulated by cortical activity. To test this hypothesis, we used functional MRI. During detection of redundant simultaneous targets, activations in the extrastriate cortex were observed in a patient with callosal agenesis and redundancy gain violating probability models, but not in a patient with callosal agenesis and redundancy gain not exceeding probability models. We conclude that cortical activity in the extrastriate cortex may be a modulating factor in the magnitude of the redundancy gain during parallel visuomotor transforms.

Agenesis of Corpus Callosum↗
PubMed2006

Diffusion tensor imaging with quantitative fibre tracking in HIV infection and alcoholism comorbidity: synergistic white matter damage.

A substantial proportion of individuals infected with human immunodeficiency virus (HIV) also abuse alcohol. Given that each condition can disrupt brain structural integrity, with a predilection for white matter, we used MR diffusion tensor imaging (DTI) and quantitative fibre tracking to examine the separate and combined effects on the microstructure of the corpus callosum. Subjects were men and women with alcoholism alone (n = 87), HIV infection alone (n = 42), alcoholism and HIV infection comorbidity (n = 52) and non-affected controls (n = 88). The two alcoholism groups had similar lifetime alcohol consumption histories; the two HIV-infected groups had similar CD4+ counts and viral loads; all groups were matched in body mass index, and no participant was demented. Compared with controls, all patient groups had lower fractional anisotropy (FA) and higher mean diffusivity (MD) in callosal regions and fibre bundles coursing through the genu and splenium, but these effects were only significant in the two groups with alcoholism, which exhibited 0.65-1.2 SD abnormalities in FA and MD. The callosal regions were differentially affected by alcoholism, with the genu more affected than the splenium, a pattern even more pronounced in the fibre tracks. When the HIV-infected groups were divided by disease severity defined as an acquired immunodeficiency syndrome (AIDS)-defining event or low CD4+ counts (<200) and alcoholism comorbidity, the HIV-infected subgroup with AIDS and alcoholism exhibited approximately 2 SD FA and MD abnormalities in the callosal sectors and fibres, abnormalities that were more than twice the effect sizes observed in the other three HIV-infected subgroups. Degradation of the callosal microstructure was consistently associated with alcoholism, with evidence for compounded alcoholism-HIV effects. Functional relevance of the microstructural abnormalities was supported by associations between motor deficits and low FA or high MD within the diagnostic groups. The high prevalence of alcoholism in HIV-infected individuals and the interfering effect of alcohol on HIV pharmacological response and therapy compliance underscore the need to recognize the independent and synergistic contributions of each condition to brain structure and function.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Developmental history of the subplate and developing white matter in the murine neocortex. Neuronal organization and relationship with the main afferent systems at embryonic and perinatal stages.

The neuronal diversity of the subplate and developing white matter in the mouse was studied using a variety of neuronal markers. The subplate was first visible in lateral cortical areas at E13, coinciding with the emergence of the cortical plate. During prenatal development, this layer was formed by morphologically heterogeneous neurons, subsets of which were immunoreactive for GABA- and calcium-binding proteins. From E18 onwards, a few subplate cells also contained neuropeptides. Colocalization experiments demonstrated that the percentages of neurons immunoreactive for each antigen were similar to those described in adult neocortex. By E15, subplate cells had received synaptic contacts. Moreover, a second early-neuronal population was conspicuous from E13 in the lower intermediate zone: the intermediate-subventricular population. Unlike subplate cells, these neurons were morphologically uniform, smaller and horizontally oriented. Nevertheless, a few of these cells also appeared within the ventricular zone, with a perpendicular/ oblique orientation. Most of these cells were GABA-positive and showed calbindin immunoreactivity. At the electron microscopic level, no synaptic contacts were found in these neurons. Tracing studies using DiI showed that subplate neurons were the first to send axons outside the neocortex towards the ganglionic eminence at E13. At E14, subplate axons and ingrowing thalamic fibers met in the striate primordium. Subplate cells retained their projection to the thalamus during prenatal development. Thalamocortical axons reached the subplate at E15, and 1 day later began to invade the upper cortical layers. Early callosal axons, in contrast, did not run through the subplate to reach the contralateral hemisphere, nor did subplate cells send out callosal fibers. Callosal axons ran just above the subventricular zone, intermingled with the intermediate-subventricular neuronal population. We conclude that the subplate neuronal population has a chemical heterogeneity reminiscent of that of the adult cortex and is crucial to the establishment of thalamocortical relationships, whereas the intermediate-subventricular neurons constituted a particular GABAergic population, which includes resident cells and tangentially migrating postmitotic neurons spatially related to the development of callosal connections.

Afferent Pathways↗
PubMed2001

Sex differences in brain maturation during childhood and adolescence.

Brain development during childhood and adolescence is characterized by both progressive myelination and regressive pruning processes. However, sex differences in brain maturation remain poorly understood. Magnetic resonance imaging was used to examine the relationships between age and sex with cerebral gray and white matter volumes and corpus callosal areas in 118 healthy children and adolescents (61 males and 57 females), aged 6-17 years. Gender groups were similar on measures of age, handedness, socioeconomic status and Full Scale IQ. Significant age-related reductions in cerebral gray and increases in white matter volumes and corpus callosal areas were evident, while intracranial and cerebral volumes did not change significantly. Significant sex by age interactions were seen for cerebral gray and white matter volumes and corpus callosal areas. Specifically, males had more prominent age-related gray matter decreases and white matter volume and corpus callosal area increases compared with females. While these data are from a cross-sectional sample and need to be replicated in a longitudinal study, the findings suggest that there are age-related sex differences in brain maturational processes. The study of age-related sex differences in cerebral pruning and myelination may aid in understanding the mechanism of several developmental neuropsychiatric disorders.

Adolescent↗
PubMed2003

The size of corpus callosum correlates with functional activation of medial motor cortical areas in bimanual and unimanual movements.

Effects of the size of corpus callosum measured from in vivo magnetic resonance imaging (MRI) recordings on cortical activations evaluated using functional MRI (fMRI) were analyzed during motor tasks. Twelve right-handed men performed unilateral finger movements and bilateral movements either with or without a temporal delay between left and right fingers. The size of the rostral part of corpus callosum and the anterior and posterior callosal truncus explained 11.9 and 15.2% of activation in the mesial frontal cortex in unimanual left and right finger movements, respectively. In bimanual simultaneous movements, 34.2% of the activated voxels in the mesial frontal cortex were related to the size of corpus callosum. In bimanual movements in which left finger movement preceded the onset of the right finger movement, the callosal size accounted for 88.7% of activation in the mesial frontal cortex. In contrast, when the right finger movement preceded the left, callosal size accounted for only 31.3% of the mesial frontal cortex activation. The correlations between callosal parameters and activation over the lateral cortex were sparse and occurred only in bimanual movements. The results suggest that corpus callosum modulates the activity of the supplementary motor and cingulate cortical areas depending on temporal complexity of bimanual movements.

Adult↗
PubMed1995

Tapetum-specific expression of the gene for an endo-beta-1,3-glucanase causes male sterility in transgenic tobacco.

A cDNA for a pathogenesis-related endo-beta-1,3-glucanase isolated from soybean, was fused to an anther tapetum-specific promoter (Osg6B promoter) isolated from rice and the resulting chimeric gene was introduced into tobacco. The Osg6B promoter became active in the anther tapetum during formation of tetrads and the tapetal glucanase activity in the transgenic plants caused in a significant reduction in the number of fertile pollen grains. Most of the pollen grains were aberrant in shape, lacked germinal apertures and aggregate of the pollen grains. Granules of beta-1,3-glucan, which have not previously been reported, were often observed to adhere to the surface of the pollen grains. Further observations revealed that the callose wall was almost absent in the pollen tetrads of transgenic plants. In wild-type plants, by contrast, the tetrads were surrounded by callose that was degraded soon after the tetrad stage to release free microspores. Thus, the introduced gene for endo-beta-1,3-endoglucanase under the control of the Osg6B promoter caused digestion of the callose wall at the beginning of the tetrad stage, a time that was just a little earlier than the time at which endogenous glucanase activity normal appears. These results demonstrate that premature dissolution of the callose wall in pollen tetrads causes male sterility and suggest that the time at which tapetally produced glucanase is activate is critical for the normal development of microspores.

Base Sequence↗
PubMedDate not supplied

A computerized approach for morphological analysis of the corpus callosum.

OBJECTIVE: A new technique for analyzing the morphology of the corpus callosum is presented, and it is applied to a group of elderly subjects. MATERIALS AND METHODS: The proposed approach normalizes subject data into the Talairach space using an elastic deformation transformation. The properties of this transformation are used as a quantitative description of the callosal shape with respect to the Talairach atlas, which is treated as a standard. In particular, a deformation function measures the enlargement/shrinkage associated with this elastic deformation. Intersubject comparisons are made by comparing deformation functions. RESULTS: This technique was applied to eight male and eight female subjects. Based on the average deformation functions of each group, the posterior region of the female corpus callosum was found to be larger than its corresponding region in the males. The average callosal shape of each group was also found, demonstrating visually the callosal shape differences between the two groups in this sample. CONCLUSION: The proposed methodology utilizes the full resolution of the data, rather than relying on global descriptions such as area measurements. The application of this methodology to an elderly group indicated sex-related differences in the callosal shape and size.

Aged↗