A study of callosal fiber degeneration in the rat and opossum by the aid of the Fink-Heimer silver technique has led to the conclusion that the intracortical distribution of the corpus callosum involves all cortical layers. Evidence was found of regional differences in the intracortical distribution pattern; in some regions a stratified mode of callosal fiber termination was apparent.
"The presence of normal fibers in human sections stained by the method of Albrecht and Fernstrom  does not make the charting of degenerating fibers unreliable, but long and tedious. Previous studies in both animal [Heimer et al., 1967] and human [Clarke and Miklossy, 1990] material have shown that the density of Nauta-stained interhemispheric afferents is highest within the lower fifth of the cerebral cortex. We therefore adopted a charting procedure that concentrated on a 600-µm-wide strip of cortex along the layer VI-white matter border. "
[Show abstract][Hide abstract] ABSTRACT: Very little is known about the connectivity of the human cerebral cortex. Nonhuman primates often serve as a model, but they are very unsatisfactory when it comes to specifically human functions. Evidence from (human) lesion and activation studies indicates that Broca's and Wernicke's areas play a critical role in language functions, whereas the inferior temporal cortex of the right hemisphere tends to be associated with high-level visual recognition. We describe here monosynaptic interhemispheric input from the right inferior temporal cortex to Wernicke's and Broca's areas. The connections were traced in a brain with a right inferior temporal infarction by means of the Nauta method for anterogradely degenerating axons. Afferents were found both in Broca's and Wernicke's areas, with a higher density in the latter. Three organizational principles emerge from this study. First, the presence of direct connections from the right inferior temporal cortex to the speech areas indicates that human interhemispheric connections can be widely heterotopic. Second, the fact that connections from the inferior temporal cortex terminate in both Wernicke's and Broca's areas speaks in favor of parallel pathways in visuo-verbal processing. And third, the patchy distribution of visual interhemispheric afferents in Wernicke's area hints at a possible functional compartmentalization within this area.
Human Brain Mapping 01/1997; 5(5):347-54. DOI:10.1002/(SICI)1097-0193(1997)5:5<347::AID-HBM3>3.0.CO;2-3 · 5.97 Impact Factor
"Not surprisingly, therefore, in the case of callosal connections attention has focused thus far on their topographical organization rather than on the morphology of callosal axons. A fundamental discovery of those studies was that of a discontinuous 'columnar' pattern of callosal terminations in rat and monkey (Heimer et al., 1967; Jones et al., 1975; Künzle, 1976), later confirmed in several areas of several species. In addition, in primary sensory areas both the origin and the termination of callosal projections were found to be circumscribed and spared large acallosal regions (for references see Innocenti, 1986). "
[Show abstract][Hide abstract] ABSTRACT: Seventeen callosally projecting axons originating near the border between areas 17 and 18 in adult cats were anterogradely labelled with biocytin and reconstructed in 3-D from serial sections. All axons terminated near the contralateral 17/18 border. However, they differed in their diameter, tangential and radial distributions, and overall geometry of terminal arbors. Diameters of reconstructed axons ranged between 0.45 and 2.25 microns. Most of the axons terminated in multiple terminal columns scattered over several square millimetres of cortex. Thus in general callosal connections are not organized according to simple, point-to-point spatial mapping rules. Usually terminal boutons were more numerous in supragranular layers; some were also found in infragranular layers, none in layer IV. However, a few axons were distributed only or mainly in layer IV, others included this layer in their termination. Thus, different callosal axons may selectively activate distinct cell populations. The geometry of terminal arbors defined two types of architecture, which were sometimes represented in the same axon: parallel architecture was characterized by branches of considerable length which supplied different columns or converged onto the same column; serial architecture was characterized by a tangentially running trunk or main branch with radial collaterals to the cortex. These architectures may relate to temporal aspects of inter-hemispheric interactions. In conclusion, communication between corresponding areas of the two hemispheres appears to use channels with different morphological and probably functional properties.
European Journal of Neuroscience 07/1994; 6(6):898-917. DOI:10.1111/j.1460-9568.1994.tb00585.x · 3.18 Impact Factor
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