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PubMed1978

Block design performance following callosal sectioning. Observations on functional recovery.

A patient with complete surgical section of the corpus callosum was tested on a constructional task 17 months post-operatively. The left and right hands were separately tested under conditions of free visual exposure and lateralized visual field exposure. The results suggest that the typically observed improved performance of the right hand with increasing postoperative time is attributable to the acquisition of homolateral control over the right hand by the right hemisphere. The implications for left-right brain organization and the syndrome of constructional apraxia are considered.

Adolescent↗
PubMed1981

Praxis and writing of the left hand may be served by different callosal pathways.

A patient who had damage to the leftward outflow of the body of the corpus callosum experienced the development of agraphia, but not apraxia, of the left hand. In another case reported recently, a similar lesion produced the same intriguing dissociation. We suggest that the principal interhemispheric controls for praxis and for writing of the left hand operate at different levels of the corpus callosum.

Adult↗
PubMed1992

Callosal morphology concurs with neurobehavioral and neuropathological findings in two neurodevelopmental disorders.

To integrate neuroimaging, neuropathologic, and neuropsychological findings, computer-assisted morphometry was applied to magnetic resonance images of the corpus callosum in adolescents with Down and Williams syndromes and in control subjects. Callosa of subjects with Down syndrome were distinctively rounded in form, consistent with Down syndrome brachycephaly. These callosa also showed decreased widths throughout their rostral fifth, which serves frontal lobe projections. This finding correlates with the hypocellularity and hypofrontality of neocortex in subjects with Down syndrome and with their neuropsychological profile of frontal lobe dysfunction. Callosa of subjects with Williams syndrome generally resembled control specimens, in congruence with their frontal lobe structure and better preserved frontal lobe function. These results represent a convergence of findings across levels of neuroscientific investigation.

Adolescent↗
PubMed1984

More intense focal seizure types after callosal section: the role of inhibition.

Corpus callosum section reduces the incidence of generalized seizures associated with loss of consciousness. Minimal data are available, however, regarding the types of seizures that may be present following surgery. Five of 17 patients in our clinic who underwent partial or complete corpus callosum section developed more intense and sometimes newly patterned (but not necessarily more frequent) focal seizures postoperatively. These patients were not predictably different from the other 12 in terms of age at onset of seizures or at surgery, cause of seizures, extent of callosum sectioned, radiographically demonstrable structural lesions, or the types of preoperative seizures. All 5 patients, however, had bilateral independent frontal electroencephalographic foci. No patients without these electroencephalographic findings developed more intense focal seizures after surgery. The findings are consistent with the results of experimental animal studies and argue for a suppressive influence of the contralateral hemisphere on some types of seizures.

Adolescent↗
PubMed1985

Origin of interhemispheric fibers in acallosal opossum (with a comparison to callosal origins in rat).

The neocortical origins of the anterior commissure in the acallosal, marsupial opossum were studied with the horseradish peroxidase (HRP) method. Following complete surgical transection of the anterior commissure, HRP was applied directly to the cut fiber tips. This procedure resulted in very large numbers of vividly labeled cells within the neocortex. The labeled cells were plotted and counted for comparison among cytoarchitectonic areas and among cortical layers. For comparative purposes, the neocortical origins of the corpus callosum are studied with the same procedure in the rat. No cytoarchitectonic area was entirely devoid of labeled cells in either species. The concentration of labeled cells throughout the entire neocortex averaged 25.2 cells/0.05 mm3 in opossum and 31.2 cells/0.05 mm3 in rat. The concentrations of labeled cells were correlated for the eight cytoarchitectonic areas common to the two species, though they were different enough in number to be statistically reliable. The distribution of labeled cells both among and within cytoarchitectonic areas was often more homogeneous in opossum than in rat. Although cortical layer 1 had no labeled cells in either species, the distribution of labeled cells across the remaining cortical layers differed sharply between the two species. In opossum, layer 3 had the most labeled cells (averaging 55% of the total number) while layer 5 had considerably less (averaging 12%). In rat, layer 5 had as many labeled cells as layer 3--both layers averaging 43% of the total number of labeled cells. In both species, striate cortex deviated markedly from other cytoarchitectonic areas. Although both species had very few labeled cells in striate cortex, those that were labeled were invariably supragranular in opossum and infragranular in rat. The similarities and dissimilarities in the topographic distribution of the origins of the two types of interhemispheric fiber systems seem to parallel the degree of cortical (and thalamic) differentiation in the two animals. However, the differences in laminar distribution are much greater and in particular, the small contribution of layer 5 in opossum as opposed to rat may well be functionally significant.

Animals↗
PubMed1992

Callosal and superior temporal sulcus contributions to receptive field properties in the macaque monkey's nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract.

To assess the functional contribution of the cortical input to the receptive field properties of nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN) neurons, a first set of experiments evaluated the response properties of NOT-DTN cells in monkeys with split corpus callosum. With respect to visual latency, direction specificity, directional tuning width, velocity tuning, ocular dominance, and binocular interaction, they were indistinguishable from NOT-DTN neurons in normal monkeys. However, a clear difference was found regarding the extent of the receptive fields. Whereas, in normal monkeys, NOT-DTN receptive fields include the contralateral hemifield and the fovea as well as substantial parts of the ipsilateral visual field, receptive fields in callosum-split monkeys stop abruptly at, or close to, the vertical 0-meridian and do not extend into the ipsilateral visual field. In addition, the location of the highest sensitivity within the receptive fields in callosum-split monkeys is shifted away from the vertical 0-meridian in comparison to normal animals. In a second set of experiments, we antidromically identified cortical neurons within the superior temporal sulcus that project to the NOT-DTN. These neurons were found in area MT mostly near the border of MTp or MSTl. All of them are direction selective for ipsiversive stimulus movement, and their receptive fields extend substantially into the ipsilateral visual hemifield. Neurons with other preferred directions did not project to the NOT-DTN. These results contribute to the explanation of the ipsiversive directional deficits in slow eye movements after cortical lesions, as well as the asymmetries in optokinetic nystagmus with hemifield stimulation after transection of the corpus callosum. The more general implication of the results is that a particular function of a cortical area can only be understood by knowing its subcortical connections.

Animals↗
PubMed1997

Lateralization of affective prosody in brain and the callosal integration of hemispheric language functions.

Although affective prosody appears to be a dominant function of the right hemisphere, its degre of lateralization has not yet been established since various publications have reported affective-prosodic deficits following left brain damage in association with aphasia. This paper explores the mechanisms underlying affective-prosodic deficits following left and right brain damage by testing the ability of subjects to repeat and comprehend affective prosody under progressively reduced verbal-articulatory conditions. The results demonstrate that reducing verbal-articulatory conditions robustly improves the performance of left but not right brain damaged patients, a finding that supports the supposition that affective prosody is strongly lateralized to the right hemisphere. However, the performance of left brain damaged patients was not correlated to the presence, severity, or type of aphasic deficit(s). Based on functional-anatomic correlations for spontaneous affective prosody and affective-prosodic repetition, deep white matter lesions located below the supplementary motor area that disrupt interhemispheric connections coursing through the mid-rostral corpus callosum may contribute to affective-prosodic deficits that are both additive and independent of any aphasic deficits. In light of these and other findings, various anatomical, functional, and maturational hierarchic relationships between the affective-prosodic and verbal-linguistic aspects of language are posited in order to help further explain discrepancies that exist in the literature regarding the neurology of affective prosody.

Adult↗
PubMed2002

A framework for callosal fiber distribution analysis.

This paper presents a framework for analyzing the spatial distribution of neural fibers in the brain, with emphasis on interhemispheric fiber bundles crossing through the corpus callosum. The proposed approach combines methodologies for fiber tracking and spatial normalization and is applied on diffusion tensor images and standard magnetic resonance images.

Adult↗
PubMed1996

Interhemispheric lipoma with variable callosal dysgenesis: relationship between embryology, morphology, and symptomatology.

Eight interhemispheric lipomas (five tubulonodular lipomas and three curvilinear lipomas) were examined by magnetic resonance imaging (MRI). The purpose was to further investigate the relationship between the morphology of the different subtypes and the clinical presentation. The imaging findings were reviewed in light of a recent theory on the development of the corpus callosum. Interhemispheric lipomas should be considered as one entity with a variable expression depending on the severity and/or the time of the insult. Curvilinear lipomas can be either small or extensive and are usually not symptomatic. Tubulonodular lipomas can be either predominantly anterior or posterior in location. The anterior subtype appears to be a more severe form of tubulonodular lipoma. The associated structural abnormalities are most likely responsible for the symptoms, rather than the lipoma itself. Magnetic resonance imaging allows a more precise timing of the insult, resulting in the development of a lipoma. The knowledge of the embryology between the 6th and the 20th week is important to explain these abnormalities. Until now it has been accepted that the corpus callosum develops in an orderly fashion. A recent theory has demonstrated that this is not necessarily true, and that fibers can cross the midline at any place irrespective of the normal development. This theory explains the sometimes amorphous appearance of the remnant of the corpus callosum if a lipoma is present.

Adolescent↗