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PubMed1982

The pattern of interhemispheric connections and its relationship to extrastriate visual areas in the macaque monkey.

The distribution of interhemispheric connections was studied in extrastriate visual cortex of the macaque monkey. Callosal fiber terminations were identified by staining for anterograde degeneration following transection of the splenium of the corpus callosum. Retrogradely labeled cell bodies of callosal projection neurons were identified histochemically following application of horseradish peroxidase to the cut surface of the callosum. Results were displayed on unfolded, two-dimensional representations of the cortex, which permitted spatial and topological relationships between callosal recipient and callosal free cortical regions to be discerned readily. The overall pattern of callosal inputs to visual cortex can be subdivided into nine callosal recipient zones which surround seven callosal free regions in the occipital, temporal, and parietal lobes. This pattern provides reliable and useful landmarks for identifying the borders of at least five topographically organized extrastriate visual areas. There is a pronounced dorsoventral asymmetry in callosal projections, not recognized in previous studies, which reflects an asymmetry in the organization of visual areas in dorsal versus ventral halves of the occipital lobe. The pattern of callosal fiber terminations is mirrored by a very similar distribution of callosal projection neurons. There are significant regional differences in the laminar distribution of callosal projection cells, and these differences may reflect functionally distinct cortical subdivisions. A considerable degree of individual variability was found in the relationship of callosal connections to gyral and sulcal landmarks as well as in the fine structure of individual callosal recipient strips, suggesting that each animal has a unique "callosal fingerprint." These findings emphasize the usefulness of the callosal pathway in elucidating the functional organization of extrastriate visual cortex.

Animals↗
PubMed1999

Anatomical correlates of alien hand syndromes.

OBJECTIVE: The objective of this study was to correlate various alien hand syndromes (AHS) with sites of lesion in 16 patients with anterior cerebral artery (ACA) territory infarction. BACKGROUND: All previous reports of AHS were case studies. Their clinico-anatomic correlations were still controversial. While the callosal lesion appears necessary for various types of AHS, which portion of the corpus callosum is associated with which syndrome is still not yet completely resolved. METHOD: Sixteen patients with ACA territory infarction were selected from a stroke registry containing 7355 individuals. They were divided into three lesion groups according to location identified by computed tomography or magnetic resonance imaging: mesial frontal, callosal and combined mesial frontal and callosal. Neurobehavioral examination focused on the presence or absence of grasp reflex, various alien hand signs, intermanual conflict, and callosal disconnection syndrome. By gross visual analysis of the obtained data, a trend for clinicoanatomic correlation emerged. RESULTS: Patients with restricted mesial frontal lesions (three subjects), restricted anterior callosal lesions (four subjects) or "restricted" mesial frontal and anterior callosal lesions (two subjects) did not have symptoms of AHS. The remaining seven patients with extensive callosal injury involving the midbody and isthmus all had symptoms of AHS. Four of the patients with relatively isolated callosal involvement showed intermanual conflict (IMC) associated with a callosal AHS, while the remaining three patients with additional lesions involving the mesial frontal cortex showed impulsive reaching and grasping behaviors of the contralesional hand (a component of frontal AHS) and IMC (a component of callosal AHS). CONCLUSIONS: A comparison of the lesions and symptoms of seven patients in two different groups shows that mesial frontal and anterior callosal (genu and rostral body) lesions are associated with a contralateral frontal AHS. Isolated involvement of the callosal midbody and isthmus is associated with a callosal AHS. When the mesial frontal cortex and corpus callosum (genu and whole body) are extensively involved, a mixed frontal and callosal AHS may occur in the same patient.

Aged↗
PubMed2000

Classification and longitudinal examination of callused teat ends in dairy cows.

To examine the development of teat end callosity thickness and roughness in early lactation and to quantify cow factors of interest, a system to classify teat end condition was developed. A distinction was made between rough and smooth rings around the teat orifice. In addition, a classification of the degree of callosity was developed. Kappa coefficients for the repeatability of scoring by this classification system by different workers were 0.71 for teat end callosity thickness and 0.86 for teat end callosity roughness. The teat end callosity classification system was used for a longitudinal study with 40 cows during the first 14 wk of lactation. Models were built to predict teat end callosity thickness and roughness, machine-on time, and milk yield. For the response variables, teat end callosity thickness, machine-on time, and milk yield, the consecutive measurements appeared to follow a lactation curve model with a subject-specific general slope and intercept. Teat end callosity increased rapidly the first 8 wk. Cow factors such as days in milk, parity, machine-on time, and teat end shape were associated with the degree of teat end callosity, and the probability of the callosity ring to become rough. Teat end callosity thickness did not decrease within the 14-wk trial period for most teats. Pointed or round teat ends showed more callus than inverted teat ends. Longer machine-on time resulted in a higher probability of the callosity ring to become rough. Rear teats showed less callosity than front teats in this study.

Animals↗
PubMed2003

Corpus callosum abnormalities in psychopathic antisocial individuals.

CONTEXT: Psychopathic antisocial individuals have previously been characterized by abnormal interhemispheric processing and callosal functioning, but there have been no studies on the structural characteristics of the corpus callosum in this group. OBJECTIVES: To assess whether (1) psychopathic individuals with antisocial personality disorder show structural and functional impairments in the corpus callosum, (2) group differences are mirrored by correlations between dimensional measures of callosal structure and psychopathy, (3) callosal abnormalities are associated with affective deficits, and (4) callosal abnormalities are independent of psychosocial deficits. DESIGN: Case-control study. SETTING: Community sample. PARTICIPANTS: Fifteen men with antisocial personality disorder and high psychopathy scores and 25 matched controls, all from a larger sample of 83 community volunteers. MAIN OUTCOME MEASURES: Structural magnetic resonance imaging measures of the corpus callosum (volume estimate of callosal white matter, thickness, length, and genu and splenium area), functional callosal measures (2 divided visual field tasks), electrodermal and cardiovascular activity during a social stressor, personality measures of affective and interpersonal deficits, and verbal and spatial ability. RESULTS: Psychopathic antisocial individuals compared with controls showed a 22.6% increase in estimated callosal white matter volume (P<.001), a 6.9% increase in callosal length (P =.002), a 15.3% reduction in callosal thickness (P =.04), and increased functional interhemispheric connectivity (P =.02). Correlational analyses in the larger unselected sample confirmed the association between antisocial personality and callosal structural abnormalities. Larger callosal volumes were associated with affective and interpersonal deficits, low autonomic stress reactivity, and low spatial ability. Callosal abnormalities were independent of psychosocial deficits. CONCLUSIONS: Corpus callosum abnormalities in psychopathic antisocial individuals may reflect atypical neurodevelopmental processes involving an arrest of early axonal pruning or increased white matter myelination. These findings may help explain affective deficits and previous findings of abnormal interhemispheric transfer in psychopathic individuals.

Adult↗
PubMed1987

Interhemispheric connections of the somatosensory cortex in the rabbit.

Corpus callosal connections of somatosensory cortex were studied in rabbits by combining anatomical tracing and electrophysiological mapping in the same animals. The results show that callosal connections are unevenly distributed in SI and SII. In SI, the representations of all body surfaces caudal to the neck and midline structures of the head have dense callosal connections. Conversely, connections are sparse to absent within representations of laterally positioned surfaces of the head, such as the sinus hairs, vibrissae, and nonmidline portions of the lips. Almost all of SII has dense callosal connections; only the representations of the vibrissae and sinus hairs have moderate callosal connections. The laminar distribution of callosal connections in rabbit SI and SII is similar to that observed in other mammals. Callosal terminations extend from the inner portion of layer I to the outer portion of layer VI, are moderately denser in the supragranular layers, and are sparse in layer IV. Callosally projecting cells are found predominantly in layers II, III, and V and are sparse in layers IV and VI. These data further emphasize the direct correspondence between the pattern of callosal connections in SI and the functional importance of particular body surfaces. Hence, representations of body surfaces important in the exploration of the environment are relatively free of callosal connections, whereas representations of midline and more lateral surfaces, less significant in tactile exploration, receive dense callosal connections. Callosal connections in rabbits are distributed extensively throughout responsive koniocortical regions rather than being relegated to distinct, specialized regions of "unresponsive" dysgranular cortex as in rodents.

Animals↗
PubMed1984

Deafferentation and axotomy of neurons in cat striate cortex: time course of changes in binocularity following corpus callosum transection.

Single neurons were recorded in the callosal terminal and cell zones of area 17 in the cat to assess the time course of changes in the proportion of binocular neurons produced by corpus callosum transection. The callosal terminal zone contains all the degenerating terminals in area 17 after corpus callosum transection. The callosal cell zone contains all the cells in area 17 which contribute axons to the corpus callosum. The cell zone is larger than, and partially overlaps, the callosal terminal zone. After corpus callosum transection there was an initial change in ocular dominance of neurons in both callosal zones. This initial change was followed by a reduction in the proportion of binocular neurons in both zones. This reduction became maximal 2-4 weeks after transection. In the callosal terminal zone, binocularity did not recover even at the longest postoperative periods examined (31-42 weeks). In the part of the callosal cell zone outside of the callosal terminal zone, the proportion of binocular neurons began to recover after 5 weeks and was at normal levels at the longest survival periods studied. Corpus callosum transection deafferents and axotomizes cells in the callosal terminal zone and, since central neurons do not regenerate their long-ranging axons, the combined effects of deafferentation and axotomy in this zone are permanent. The callosal cell zone outside of the callosal terminal zone contains axotomized cells and no degenerating terminals following transection. The recovery of binocularity in this region may be attributed to the transient changes which axotomized cells undergo. The zone which contains no callosal cells or terminals is unaffected by transection of the corpus callosum.

Animals↗
PubMedDate not supplied

Transient axonal branching in the developing corpus callosum.

During development, there is a transient overproduction of axons in the corpus callosum; this overproduction of axons is due, in part, to a transient excess of neurons that send an axon through the corpus callosum. However, transient axonal branching could also contribute to the developmental overproduction of callosal axons. To investigate this possibility, we filled developing callosal axons in the Syrian hamster with the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). Light microscopic analysis showed that, indeed, developing callosal axons branch transiently in the hamster: branching was robust on postnatal day 0 (P0) and P3 (P0 = the first 24 hr after birth), less prominent on P6 and P8, and absent by P11. Immature callosal axons branched before or after crossing the midline and at all rostral-caudal and medial-lateral levels within the corpus callosum. The majority of callosal axon collaterals that were contained within individual 100-micron-thick sections were relatively short (mean = 15.1 microns) but some collaterals extended up to approximately 135 microns from the main axon trunk before passing out of the section in which they were observed. Nearly all of the collaterals emanated from the main axon trunk; higher-order collaterals were rare. Some callosal axon trunks had multiple collaterals. Branching callosal axons originated from multiple cortical areas, including area 17. Electron microscopic observations indicated that the processes designated as axon collaterals by light microscopic criteria would have been included in electron microscopic counts of developing callosal axons. Some callosal axon trunks and branches had ultrastructural features that suggested they were degenerating. In cats, developing callosal axons branch on embryonic day 57 (E57; the first 24 hr after conception = E0) and P0. Thus, it is likely that transient branching of immature callosal axons is a generalized feature of mammalian cortical development and that it contributes to the overproduction of callosal axons, albeit perhaps to varying degrees, in multiple species.

Aging↗
PubMed1994

Analysis of cross-sectional area measurements of the corpus callosum adjusted for brain size in male and female subjects from childhood to adulthood.

Interest in anatomic evaluation of the corpus callosum is based upon the expectation that its function will be influenced by its structure. Using MR images, the size of the corpus callosum was determined by measuring its area in the midsagittal plane. A callosal index was calculated for each subject by dividing the callosal size by cerebral size, also measured from the MR image. This callosal index was designed to allow comparison of callosal size between different groups, despite differences in brain size that existed between the groups. The validity of this index was supported by the statistically significant, positive correlation between measured callosal area and cerebral size. Using MR images and the callosal index, adult males were shown to have a larger corpus callosum and larger cerebrum, compared to adult females. However, the callosal index was identical for male and female subjects. This demonstrated there relative size of the callosum was the same for males and females. Childhood development of the corpus callosum was documented through the first two decades of life by a progressive increase in the callosal index. In adults, cerebral atrophy caused a decline in callosal size, but no decline due to simple advancing age was found in normal adult subjects. This use of cerebral size to calculate a callosal index appeared to be useful in comparing callosal size between subjects and may be useful in future study of other disease states of the corpus callosum.

Adolescent↗
PubMedDate not supplied

Transitory corpus callosum axons projecting throughout developing rat visual cortex revealed by Dil.

Anatomical tracing was used to determine the extent and distribution of CC axons in mammalian visual cortex. Postnatal development of rat CC was studied by in vitro callosal labeling with the lipophilic carbocyanine dye Dil in 59 rats. Solid Dil crystals were placed in the mid-sagittal region of the CC in aldehyde-fixed brain slabs. Coronal sections through visual cortex were photographed and reconstructed to show the overall distribution of Dil-labeled callosal projections as well as the locations of individual callosal axons and their presumed synaptic boutons. During postnatal weeks 1 and 2, CC axons were found to project to layer I throughout the entire mediolateral extent of areas 17, 18a, and 18b. Numerous varicosities on callosal axons are located en passant and at axon terminals in layer I. During postnatal week 3 the tangential density of callosal projections was significantly reduced, so that fewer callosal axons extended to layer I throughout areas 17, 18a, and 18b than in younger postnatal rats. However, at this age some CC axons could still be found extending to layer I throughout the mediolateral extent of areas 17, 18a, and 18b. By postnatal week 4 the tangential distribution of callosal projections was greatly restricted; most callosal axons projecting to layer I were located at the borders of the visual cortical areas. Nevertheless, there were still callosal axons projecting into cortex and terminating in supragranular and infragranular layers in areas 17, 18a, and 18b; this was most pronounced in area 18a. Thus, in the rat there are many elaborately formed transitory CC axons projecting throughout visual cortex for several weeks postnatal. These projections extend to layer I and have varicosities in all cortical layers. With increasing age, fewer axons extended to layer I; subsequently most axons not at cytoarchitectonic borders fail to extend to layer I. If some of the varicosities on the transitory rat callosal axons were to form synapses, there would be extensive opportunities for the CC to provide input to all layers of visual cortical areas while cortical microcircuitry is being established. The same type of study in the cat has shown similar results during early postnatal development. Cat CC axons project to all parts of primary and association visual cortical areas; even in regions found to be acallosal in the adult, the neonatal callosal axons extend through all layers of cortex to reach layer I (Elberger, 1993).(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed2003

Retinal influences specify cortico-cortical maps by postnatal day six in rats and mice.

Studies of callosal projections in striate cortex show that the retina is involved in the development of topographical connections. In normal animals callosal fibers connect retinotopically corresponding, nonmirror-symmetric cortical loci, whereas in animals bilaterally enucleated at birth, callosal fibers connect topographically mismatched, mirror-symmetric loci. Moreover, in rodents the overall pattern of visual callosal connections is adult-like by postnatal day 12 (P12). In this study we delayed the onset of retinal deafferentation in rats and mice in order to determine the period when retinal influences are critically needed for the development of retinotopically matched callosal linkages. Callosal maps were revealed by placing small injections of retrogradely and anterogradely transported tracers into different loci of lateral striate cortex. We found that the patterns of callosal linkages in rats enucleated at P12, P8, and P6 were nonmirror-symmetric, as in normally reared rats. In contrast, the patterns of linkages in rats enucleated at P4 closely resembled the mirror-symmetric pattern seen in rats enucleated at birth (P0). A similar reversal in topography (from symmetric to nonsymmetric) occurred in mice when enucleation was delayed from P4 to P6. These findings indicate that retinal input prior to P6, but not prior to P4, is sufficient for specifying normal callosal topography. Moreover, they suggest that development of retinotopically matched callosal linkages depends critically on retinal influences during a brief period between P4 and P6, when callosal connections are still very immature.

Animals↗
PubMed2005

Corpus callosum in neurodegenerative diseases: findings in Parkinson's disease.

Corpus callosum area has been examined in neurodegenerative diseases as a marker for cortical pathology and for differential diagnosis; however, it has not been examined in Parkinson's disease (PD). We compared callosal area in patients with PD and PD with dementia (PDD) to healthy controls and patients with Alzheimer's disease (AD). We subsequently compared our results to a meta-analysis of studies examining callosal area in AD, frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). For the imaging study, midsagittal T1-weighted MRIs were analyzed and the callosal area was determined in patients with PD (n = 24), PDD (n = 25), AD (n = 16) and controls (n = 27). The meta-analysis combined results from all publications (Medline or PubMed) representing unique samples and measuring callosal area in AD, FTD, PSP, and CBD. We found that PD and PDD patients did not show statistically significant callosal atrophy compared to controls (effect size d, 95% CI, d = 0.13, -0.26 to 0.52, and d = 0.05, -0.44 to 0.33, respectively) or AD. The AD patients had a significant loss of callosal area compared to controls (d = -0.58, -1.01 to -0.15). Dementia severity was correlated with total callosal atrophy in AD (R = 0.66, p < 0.01) but not in PDD patients (R = 0.18, p > 0.1). The meta-analysis revealed significant combined effect sizes for callosal atrophy of: AD (d = -1.03, -1.13 to -0.93), FTD (d = -1.21, -1.56 to -0.86), PSP (d = -1.09, -1.38 to -0.81), and CBD (d = -1.80, -2.18 to -1.43). We conclude that PD and PDD patients do not have callosal atrophy in contrast to other neurodegenerative diseases, including AD. Callosal atrophy was correlated with dementia severity in patients with AD but not PDD.

Aged↗
PubMed1984

Interhemispheric connections of the visual cortex in the grey squirrel (Sciurus carolinensis).

The total pattern of visual callosal connections was studied in the grey squirrel by using the Fink-Heimer technique for axonal and terminal degeneration and the autoradiographic and horseradish peroxidase techniques for axonal transport. The pattern of terminations was correlated with architectonic landmarks. The results show that callosal terminations are distributed in a complex fashion within the visual cortical areas. The major terminations form a band in area 17 along its border with area 18. This band is contiguous rostrally with the callosal terminations in area L that extend caudomedially onto the medial wall of the hemisphere. Caudally the band in area 17 wraps around the ventral aspect of the occipital pole and ends medially at the level of the hippocampus. This band exhibits a distinct periodicity in the density of terminations. The callosal terminations in area 18 are usually found along the lateral and medial borders and are concentrated in discrete patches. The pattern in area 19 exhibits two or three primary patches and only loosely corresponds to the borders of the area. Few callosal terminations are found in area 19p and the posterior temporal area, Tp, while the intermediate temporal area, Ti, receives an extensive input. The laminar distribution of callosal terminations is different in each area studied. Characteristically, area 18 has dense terminations in layers III, II, and the inner one-half of layer I, with less dense terminations in layers V and VI, and sparse terminations in layer IV. Area 17 has a similar pattern in the supragranular and infragranular layers but also has dense terminations in layer IV. The patterns in area 19 are intermediate between these extremes but are more similar to those in area 17. The cells that give rise to the callosal projections were found primarily in layers III and V and occasionally in layers II, IV, and VI. The distribution of the callosal efferent neurons is more extensive than the areas of terminations. The distribution of callosal terminations suggests that the organization of visual cortical areas in the grey squirrel is more complex than had been previously recognized. This finding is discussed with reference to the general organization of the mammalian visual cortical areas, and a need for more extensive analyses of visual cortical areas in the grey squirrel, particularly with respect to extrastriate visual areas, is indicated.

Animals↗
PubMed1997

Dysgenesis of the corpus callosum and associated telencephalic anomalies: MRI.

We analysed the MRI findings in 23 patients with callosal dysgenesis in relation to their associated telencephalic anomalies to investigate the morphological significance of the development of Probst's bundles and the anterior commissure in congenital callosal dysgenesis. We classified callosal dysgenesis into three types: total defect (9 patients), partial defect (7) and hypoplasia (7). Associated anomalies were observed in 15 patients, including migration disorder (8 patients), micrencephaly (5), and lipoma (2). The remaining 8 patients had no associated anomalies. Probst's bundles were not identified in 4 patients with a severe migration disorder. An absent or hypoplastic anterior commissure was observed in 9 of the 16 patients with callosal defect and all 7 of those with callosal hypoplasia. Colpocephaly and keyhole dilatation of the temporal horns were seen in 16 and 21 patients, respectively. Callosal dysgenesis may occur not only through a defect in the callosal anlage, but also from impaired growth of axonal fibres projecting from the cerebral isocortex. Therefore, associated telencephalic anomalies may be responsible for additional features in callosal dysgenesis. Consequently, identification of Probst's bundles and the anterior commissure may be important when assessing cortical development in patients with callosal dysgenesis.

Abnormalities, Multiple↗
PubMed1999

Effects of prenatal gamma irradiation on the development of the corpus callosum of Swiss mice.

The temporal sequence of events related to the effects of prenatal gamma irradiation on the development of the corpus callosum and cerebral cortex was studied in Swiss mice. Pregnant females on gestational day 16 were exposed to a 60Co source receiving total doses of 2 or 3 Gy. The offspring were analyzed at both prenatal and postnatal days. One day after irradiation, a great number of pyknotic figures was seen along the whole extension of the cerebral wall, especially in the proliferative zones. At perinatal ages, the thickness of the proliferative zones was reduced and the glial sling was never identified. From 5 days after birth onwards, we observed a severe shrinkage of layers II + III and IV. The majority of the irradiated mice were totally acallosal (particularly when the 3 Gy dose was used), but some animals presented callosal remnants. These remnants were identified above the ventral hippocampal commissure, except for two animals in which a larger callosal remnant extended from the columns of the fornix to the dorsal hippocampal commissure. The presence of callosal remnants in animals irradiated with 3 Gy was dependent on the age at which the animals were analyzed since remnants were observed in some animals analyzed at perinatal ages, but never in older animals. Callosal defects can be explained at least by three factors: (1) Death of a great part of callosal neurons located at layer III. (2) Postnatal axonal elimination. (3) Absence of the glial sling. The callosal agenesis in the absence of the glial sling indicates that this structure may play a crucial role in guiding callosal axons. However, the presence of callosal remnants indicates that surviving callosal axons can use structures other than the sling to cross the midplane. Our data indicate that axons of the middle portion of the callosum can cross the midplane using the ventral hippocampal commissure as a guide. Additionally, the dorsal hippocampal commissure may play a role in directing axons of the posterior part of the corpus callosum.

Aging↗
PubMed2003

Relationships between sulcal asymmetries and corpus callosum size: gender and handedness effects.

Magnetic resonance imaging was used to establish the presence and nature of relationships between sulcal asymmetries and mid-sagittal callosal size in neurologically intact subjects, and to determine the influences of sex and handedness. Against a background of long-standing disputes, effects of gender and handedness on callosal size, shape, and variability were additionally examined. Both positive and negative correlations between sulcal asymmetry and callosal size were observed, with effects influenced by sex and handedness. The direction of relationships, however, were dependent on the regional asymmetry measured and on whether real or absolute values were used to quantify sulcal asymmetries. Callosal measurements showed no significant effects of sex or handedness, although subtle differences in callosal shape were observed in anterior and posterior regions between males and females and surface variability was increased in males. Individual variations in callosal size appear to outrange any detectable divergences in size between groups. Relationships between sulcal asymmetries and callosal size, however, are influenced by both sex and handedness. Whether magnitudes of asymmetry are related to increases or decreases in callosal size appears dependent on the chosen indicators of asymmetry. It is an oversimplification, therefore, to assume a single relationship exists between cerebral asymmetries and callosal connections.

Adult↗
PubMed2006

Transient cellular structures in developing corpus callosum of the human brain.

The corpus callosum connects two cerebral hemispheres as the most voluminous fiber system in the human brain. The developing callosal fibers originate from immature pyramidal neurons, grow through complex pathways and cross the midline using different substrates in transient fetal structures. We analyzed cellular structures in the human corpus callosum on postmortem brains from the age of 18 weeks post conception to adult, using glial fibrillary acidic protein, neuron-specific nuclear protein, and chondroitin sulphate immunocytochemistry. We found the presence of transient cellular structures, callosal septa, which divide major fiber bundles and ventrally merge with subcallosal zone forming grooves for callosal axons. The callosal septa are composed of glial fibrillary acidic protein reactive meshwork, neurones and the chondroitin sulphate immunoreactive extracellular matrix. The developmental window of prominence of the callosal septa is between 18-34 weeks post conception which corresponds to the period of most intensive growth of callosal axons in human. During the early postnatal period the callosal septa become thinner and shorter, lose their neuronal and chondroitin sulphate content. In conclusion, transient expression of neuronal, glial and extracellular, growing substrate in the callosal septa, as septa itself, indicates their role in guidance during intensive growth of callosal fibers in the human brain. These findings shed some light on the complex morphogenetic events during the growth of the corpus callosum and represent normative parameters necessary for studies of structural plasticity after perinatal lesions.

Adult↗
PubMed1981

Laminar connections of the cat's auditory cortex.

The retrograde and the anterograde transport of horseradish peroxidase were used to study the connections established by cells in different layers of the cat's primary auditory cortex (AI). Injections of peroxidase into the medial geniculate body show that pyramidal cells in layers V and VI of AI are the sources of the corticothalamic projections. Large pyramidal cells in the outer rim of layer V also send their axons to the inferior colliculus, and it is possible that some of these cells have axons that branch to innervate both the inferior colliculus and the medial geniculate body. Cells in AI that give rise to callosal axons lie principally in layers III and VI. The callosal neurons are found in irregular clusters as wide as 1100 microgram separated by spaces that contain relatively few callosal neurons. Experiments utilizing the anterograde transport of peroxidase show that callosal terminals are found in bands running from layers VI through I. These bands are about 500 microgram in width, and the terminals seem most densely packed in layers II and III. Since the dimensions of the cell clusters and bands of callosal terminals are not the same, it is likely that not all zones which give rise to callosal axons also receive them. The bands of callosal terminals labeled by orthograde transport may be seen in the same section along with the cell bodies labeled by retrograde transport, and the two zones of label are clearly not coextensive. Complete reciprocity, therefore, seems to be absent in the callosal auditory pathway.

Animals↗
PubMed2005

Corpus callosum size correlates with asymmetric performance on a dichotic listening task in healthy aging but not in Alzheimer's disease.

Alzheimer's disease (AD) involves not only gray matter but also white matter pathology, as reflected by atrophy of the corpus callosum (CC). Since decreased CC size may indicate reduced functional interhemispheric connectivity, differences in callosal size may have cognitive consequences that may become specifically apparent in neuropsychological tasks that tap hemispheric laterality. In the present study, we examined callosal functioning with a dichotic listening task in 25 Alzheimer patients, 20 healthy elderly and 20 healthy elderly with subjective memory complaints. We found decreased performance, increased ear asymmetry, and decreased callosal size in the AD group compared to healthy elderly. As expected, in the healthy elderly, we found significant negative correlations between ear asymmetry and callosal size, specifically in the anterior and posterior callosal subareas. While the association with the posterior subareas (isthmus and splenium) points at involvement of temporal areas mediating language processing, the association with the anterior subarea (the rostrum and genu) points at involvement of frontal areas mediating attention and executive functions. Remarkably however, in contrast to the healthy elderly, callosal size was not related to ear asymmetry in the AD group. The absence of an association between callosal atrophy and ear asymmetry implies that other pathological processes, next to reduced callosal functioning, attribute to ear asymmetry in AD. Difficulties to attend specifically to the left ear during dichotic listening in some of the AD patients, points at decreased attention and executive functions and suggests that pathology of specifically the frontal areas is involved.

Aged↗