Abstract
The splenium of the corpus callosum connects the posterior cortices with fibers varying in size from thin late-myelinating axons in the anterior part, predominantly connecting parietal and temporal areas, to thick early-myelinating fibers in the posterior part, linking primary and secondary visual areas. In the adult human brain, the function of the splenium in a given area is defined by the specialization of the area and implemented via excitation and/or suppression of the contralateral homotopic and heterotopic areas at the same or different level of visual hierarchy. These mechanisms are facilitated by interhemispheric synchronization of oscillatory activity, also supported by the splenium. In postnatal ontogenesis, structural MRI reveals a protracted formation of the splenium during the first two decades of human life. In doing so, the slow myelination of the splenium correlates with the formation of interhemispheric excitatory influences in the extrastriate areas and the EEG synchronization, while the gradual increase of inhibitory effects in the striate cortex is linked to the local inhibitory circuitry. Reshaping interactions between interhemispherically distributed networks under various perceptual contexts allows sparsification of responses to superfluous information from the visual environment, leading to a reduction of metabolic and structural redundancy in a child's brain.
Highlights
The splenium is a name of the posterior part of the corpus callosum (CC)
This paper addresses the structural and functional development of the splenium based on the recent literature with an emphasis on the heterogeneity of its functions and mechanisms at different levels of the visual hierarchy
Since the end of the 1990s, several laboratories have applied mesh-based computational MRI techniques to the analysis of the sagittal callosal area in children and adolescents [27,28,29,30]. In this method, aimed toward longitudinal research, four-dimensional quantitative maps of growth patterns are reconstructed by computing a threedimensional elastic deformation field, which rearranges the shape of the CC in the earlier scan into the shape in the later scan [30]
Summary
The splenium is a name of the posterior part of the corpus callosum (CC). In Greek this word means a bandage strip tied around an injury or a damaged part of someone’s body. They are relatively dense and widely distributed in the extrastriate cortices, whereas in the striate cortex, callosal fibers are located in a narrow strip along the V1/V2 border representing the vertical meridian of the visual field These basic aspects of the splenium organization are supplemented by recent neuroimaging findings. The neuroimaging data question some features of splenial connectivity that had been established in animal and postmortem human studies These include the notion that the primary visual cortex is mostly devoid of callosal connections: significant interindividual variability of connections between the striate cortices (with one-third of participants exhibiting direct interhemispheric projections in this area) has been found by Putnam and colleagues [12]. This paper addresses the structural and functional development of the splenium based on the recent literature with an emphasis on the heterogeneity of its functions and mechanisms at different levels of the visual hierarchy
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