The body callosum is a white issue tract that connects the cerebral hemispheres, facilitating interhemispheric connectivity.

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From: The Neuroscience the Autism Spectrum Disorders, 2013

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The body callosum is created of numerous nerve fibers that connect the 2 halves that the brain. These fibers traveling with each other from one cerebral hemisphere come the other form a mind structure easily visible to the start student that neuroanatomy. Number 1 shows a saggital ar of the brain, i m sorry is a part that operation from front to back on a vertical plane. This slice passes through the midline. The large curved structure in the middle of the brain is the body callosum.


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Although over there is significant variability in the size and shape of the corpus callosum in humans, it is recognized that it contains about 200 million fibers that lug neural signals from one next of the mind to the other. Although most of this fibers room thought to be excitatory, their result may be inhibitory because of the task of inhibitory interneurons. Approximately half of these fibers are little and unmyelinated. These fibers transmit information much more slowly than the bigger myelinated axons, which are qualified of very rapid transmission of information. Several of the fibers affix to similar areas in the right and left hemispheres; other fibers walk to locations in the contralateral hemisphere that room analogous to locations that have dense ipsilateral connections with their area the origin. A last group that fibers room diffusely connected to the contralateral hemisphere. If over there is one analogy in the human mind with result reported in the animal literature, some neurons may cross the callosum and also descend to the subcortical structures prior to terminating.

Fibers native different locations of the cortex cross the callosum in discrete locations. To know this phenomenon, the is essential to study the departments of the corpus callosum (Fig. 1). The most anterior component of the callosum is the rostrum. Just behind the rostrum, the callosum bends to form the genu (or knee) and also then extend posteriorly in the body. The human body constricts contempt to end up being the isthmus and also finally terminates in the slightly bulbous splenium. Over there is a good deal of separation, personal, instance variation in the shape and also thickness the the different parts the the callosum. There have been attempts to understand distinctions in the anatomy that the right and left hemispheres and in the lateralization of duty with regard to the morphology the the body callosum. As behavior claims regarding the contribute of different areas of the callosum become an ext precise, that will end up being more an important to have the ability to carefully specify the locations of the callosum in which particular fibers cross. Currently, however, the locations are conventionally defined as proportions of the length of the callosum. There seems to it is in minimal distinction whether the curvature the the callosum is taken into account or simply maximum anterior and also posterior extension is offered for the partition. The anterior one-fourth of the callosum is thought about the genu. The rostral body starts directly behind the genu, extending earlier to include the anterior one-third of the callosum. The facility one-third of the callosum is separation into 2 equal sections, the anterior and posterior midbody. The isthmus extends indigenous the posterior one-third to the posterior one-fifth that the callosum. Finally, the many posterior one-fifth is considered the splenium. Due to the fact that these interpretations are arbitrary, they may differ in detail from investigator come investigator, depending on the investigator's emphasis.


Generally, however, that is thought that the fibers that pass with the various regions that the body callosum stand for the anterior-to-posterior organization of the cerebral cortex (Fig. 2). Deepak Pandya and Benjamin Seltzer demonstrated an anterior-to-posterior organization of the callosal yarn of i in the rhesus monkey. Prefrontal cortex and also premotor cortex axons overcome in the rostrum and also genu. Motor and somatosensory axons are found primarily in the body. Auditory and association areas are stood for in the isthmus and also visual locations in the splenium. Stephen Lomber and also colleagues file a similar arrangement in the corpus callosum of the cat, back auditory yarn are found throughout the body and also dorsal splenium, largely overlapping with limbic and visual fibers except in the really ventral sections of the splenium, i m sorry are totally visual. The very same anterior-to-posterior organization has actually been prove by Marie Christine de Lacoste and also colleagues in the person brain. The is, the right and also left prefrontal, orbital–frontal, and frontal language areas are associated in the rostrum and also the genu. The anterior part of the human body carries yarn from the sensory and also motor areas that abut the central sulcus. It appears that yarn from the area roughly the Sylvian fissure, associated with language duty in the left hemisphere, overcome in the posterior part of the human body or isthmus. Finally, the splenium carries fibers connecting the visual locations of the occipital lobe.


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Figure 2. Locations of the cortex whereby fibers that the body callosum originate space coded to match the section of the corpus callosum where those fibers overcome to the other hemisphere (adapted indigenous M. C. DeLacoste, J. B. Kirkpatrick, and also A. D. Ross, Topography that the human corpus callosum, J. Neuropathol. Exp. Neurol. 44, 578–591, 1985).


Although it is now well-known that there are distinctive behavior deficits connected with lesions come some regions of the callosum, contribute of the corpus callosum to behavior have no been simple to observe and also understand. Some scientists have said that evolution evidence says that the corpus callosum dram a distinctive duty in human behavior. The callosum is not present in part primitive marsupials and also takes on greatly increased prominence in the person species. The prominence of the body callosum shows up to boost as lateralization increases, but this partnership is currently really speculative. In fact, James Rilling and also Thomas Insel controversy that, based on studies of 11 primate species, just the size of the splenium rises in proportion come increasing mind size, conversely, the size of the corpus callosum as well as that of the anterior commissure room actually lessened relative come the dimension of other structures in higher primates. This observation suggests that any changes in the callosum related to human advancement are particular to certain areas that the callosum such as the splenium.


Developmentally, the callosum is a small structure in the neonatal brain that increases in size and prominence together the fibers myelinate (Fig. 3). At approximately 7 mainly of gestation, the lamina terminalis begins to thicken creating the commissural plate. By around 9 weeks cells begin to form the massa commissurelis, which support the growth of the very first commissural yarn at approximately 12 weeks. The basic structure that the callosum is present by 20 weeks and it continues to thicken and develop until birth, with advancement of the genu and body emerging before the of the splenium and rostrum. The myelinization the the body callosum is not believed to be finish until puberty, and also recent evidence argues that it reaches the maximum size at approximately age 25. It has been suggested that the distinctive evolutionary and developmental patterns imply a special role for the callosum in human behavior. Sandra Witelson has suggested strongly that the anatomy that the callosum may be an essential to expertise developmental issues of lateralization and hemispheric specialization. Deliniating that duty has proven difficult.

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Figure 3. Relative size of the corpus callosum is viewed in in ~ 16 main (A), 40 mainly (B), and at adulthood (C) (adapted native S. P. Springer and also G. Deutsch, Left Brain, ideal Brain: Perspectives native Cognitive Neuroscience. P. 260. Freeman, new York, 1997).