Cross-Species and Intraspecies Morphometric Analysis of the Corpus Callosum

Olivares, Ricardo; Michalland, Susana; Aboitiz, Francisco

doi:10.1159/000006640

Cited by 35 publications

(43 citation statements)

References 32 publications

(48 reference statements)

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“…54). This notion is consistent with observations that the thickest callosal fibers, those serving primary and unimodal areas, scale with brain size across species, but the thinnest ones, those serving association areas, do not (55). Moreover, a recent clinical study found that homotopic functional connections are disrupted across a wide range of psychiatric conditions, including attention deficit hyperactivity disorder, major depression, and schizophrenia (56), raising the possibility that homotopic coherence may be a universal attribute of healthy brain function.…”

Section: Discussionsupporting

confidence: 91%

Stable long-range interhemispheric coordination is supported by direct anatomical projections

Shen¹,

Mišić

Cipollini

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

118

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The functional interaction between the brain's two hemispheres includes a unique set of connections between corresponding regions in opposite hemispheres (i.e., homotopic regions) that are consistently reported to be exceptionally strong compared with other interhemispheric (i.e., heterotopic) connections. The strength of homotopic functional connectivity (FC) is thought to be mediated by the regions' shared functional roles and their structural connectivity. Recently, homotopic FC was reported to be stable over time despite the presence of dynamic FC across both intrahemispheric and heterotopic connections. Here we build on this work by considering whether homotopic FC is also stable across conditions. We additionally test the hypothesis that strong and stable homotopic FC is supported by the underlying structural connectivity. Consistent with previous findings, interhemispheric FC between homotopic regions were significantly stronger in both humans and macaques. Across conditions, homotopic FC was most resistant to change and therefore was more stable than heterotopic or intrahemispheric connections. Across time, homotopic FC had significantly greater temporal stability than other types of connections. Temporal stability of homotopic FC was facilitated by direct anatomical projections. Importantly, temporal stability varied with the change in conductive properties of callosal axons along the anterior-posterior axis. Taken together, these findings suggest a notable role for the corpus callosum in maintaining stable functional communication between hemispheres.functional connectivity | structural connectivity | homotopy | dynamics T he brain's capacity for processing information relies on a modular and hierarchical functional architecture that allows both functional segregation and integration (1, 2). Distributed processing occurs within segregated communities responsible for highly specialized functions, whereas more comprehensive functions require long-range integration across communities. This long-range integration is especially important for coordinating functions between the two hemispheres. Functional connectivity (FC), computed as the temporal correlation or covariance between regionwise signals, varies across different interhemispheric regions. FC is significantly stronger between homotopic regions than between heterotopic regions (3) and is greater than would be expected from the anatomical distance between the homotopic regions (4). This strong homotopic FC is thought to be mediated by the strong underlying structural connectivity of the corpus callosum (CC). Indeed, the majority of callosal fibers are between homotopic brain regions (5-7), and the loss of callosal integrity leads to a loss in homotopic FC (8, 9).Recently, a growing number of resting-state functional MRI (fMRI) studies have reported how FC varies over time (10). Flexibility in cognitive processing is thought to arise from the ability of certain regions to participate dynamically in different network configurations (11). For instance, ...

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Section: Discussionsupporting

confidence: 91%

Stable long-range interhemispheric coordination is supported by direct anatomical projections

Shen¹,

Mišić

Cipollini

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

118

View full text Add to dashboard Cite

show abstract

“…There is only a small contingent of fibers of very wide diameter whose caliber increases with increasing brain weight, but their increase in maximal diameter may not be sufficient to fully compensate for the increasingly long interhemispheric distances (10). Furthermore, across species the proportion of callosal fibers in relation to brain size or to the estimated numbers of cortical cells tends to decrease with increasing brain weight (10,51,52), thereby reducing the degree of interhemispheric connectivity. Overall, this evidence suggests that reduced callosal transmission is related to increased brain size, which is consistent with the hypothesis of Ringo et al (48).…”

Section: Relation To Brain Lateralizationmentioning

confidence: 99%

One hundred million years of interhemispheric communication: the history of the corpus callosum

Aboitiz

Montiel

2003

Braz J Med Biol Res

331

223

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Analysis of regional corpus callosum fiber composition reveals that callosal regions connecting primary and secondary sensory areas tend to have higher proportions of coarse-diameter, highly myelinated fibers than callosal regions connecting so-called higher-order areas. This suggests that in primary/secondary sensory areas there are strong timing constraints for interhemispheric communication, which may be related to the process of midline fusion of the two sensory hemifields across the hemispheres. We postulate that the evolutionary origin of the corpus callosum in placental mammals is related to the mechanism of midline fusion in the sensory cortices, which only in mammals receive a topographically organized representation of the sensory surfaces. The early corpus callosum may have also served as a substrate for growth of fibers connecting higher-order areas, which possibly participated in the propagation of neuronal ensembles of synchronized activity between the hemispheres. However, as brains became much larger, the increasingly longer interhemispheric distance may have worked as a constraint for efficient callosal transmission. Callosal fiber composition tends to be quite uniform across species with different brain sizes, suggesting that the delay in callosal transmission is longer in bigger brains. There is only a small subset of large-diameter callosal fibers whose size increases with increasing interhemispheric distance. These limitations in interhemispheric connectivity may have favored the development of brain lateralization in some species like humans.

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“…Combining our results and the data by Haug [1987], the exponential relation between callosal fibers (larger than 0.1 µm) and cortical cells should be about two thirds across species. This suggests that the proportion of callosal-projecting cells decreases in larger brains, perhaps contributing to an impairment of interhemispheric communication [Olivares et al, 2000], and producing an additional mechanism for hemispheric isolation besides interhemispheric transmission delay [Ringo et al, 1994].…”

Section: Fiber Number and Callosal/brain Sizementioning

confidence: 99%

“…One goal of the paper is therefore to test the concept that across species interhemispheric transmission time depends on brain size. We have chosen the callosal splenium (posterior fifth) because this structure has been the subject of previous studies [Swadlow et al, 1980;Kim et al, 1996;Kim and Juraska, 1997], is known to be involved in sensory transfer, especially visual [Hamilton, 1982;Pandya and Seltzer, 1986], and recent evidence suggests that there are species differences in this region relative to visual capacities [Olivares et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

Species Differences and Similarities in the Fine Structure of the Mammalian Corpus callosum

Olivares

Montiel²,

Aboitiz³

2001

Brain Behav Evol

Self Cite

142

122

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A cross-species ultrastructural study of the corpus callosum was performed in six domestic species: the rat, the rabbit, the cat, the dog, the horse and the cow. The results indicate cross-species conservatism in callosal fiber composition with a good interspecies relation between fiber number and brain size. Across species, increases in both brain size and callosal area indicate more callosal fibers, although less than expected from the estimated increase in cortical cell number. Within each species, the correlation between fiber number and brain weight tends to disappear, although in most cases a larger callosum implies a larger number of callosal fibers. The median fiber diameter was conservative across species (0.11–0.2 µm), indicating the maintenance of conduction velocity of most callosal fibers regardless of interhemispheric distance. Nevertheless, the maximal fiber diameters tended to be higher in species with larger brains. Therefore, there is a population of coarse-diameter fibers that tend to increase their diameter and conduction velocity with increasing brain size. However, allometric calculations suggest that the associated increase in velocity in these large fibers may not be sufficient to maintain a constant interhemispheric transmission time in different species.

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Cross-Species and Intraspecies Morphometric Analysis of the Corpus Callosum

Cited by 35 publications

References 32 publications

Stable long-range interhemispheric coordination is supported by direct anatomical projections

Stable long-range interhemispheric coordination is supported by direct anatomical projections

One hundred million years of interhemispheric communication: the history of the corpus callosum

Species Differences and Similarities in the Fine Structure of the Mammalian Corpus callosum

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