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

You are watching: The corpus callosum is a wide band of axon fibers that

From: The Neuroscience the Autism Spectrum Disorders, 2013

Related terms:


The body callosum is written of numerous nerve fibers that affix the 2 halves of the brain. This fibers traveling with each other from one cerebral hemisphere come the other form a mind structure easily visible come the beginning student of neuroanatomy. Figure 1 shows a saggital ar of the brain, i beg your pardon is a part that operation from prior to back on a upright plane. This slice passes v the midline. The large curved structure in the middle of the brain is the body callosum.


*

Although there is substantial variability in the size and shape of the body callosum in humans, it is known that that contains approximately 200 million yarn that bring neural signal from one next of the brain to the other. Although most of these fibers are thought to be excitatory, their effect may be inhibitory due to the task of inhibitory interneurons. Approximately fifty percent of this fibers are little and unmyelinated. This fibers transmit information much more slowly than the bigger myelinated axons, i beg your pardon are capable of incredibly rapid transmission of information. Some of the fibers attach to similar areas in the right and left hemispheres; various other fibers go to locations in the contralateral hemisphere that are analogous to locations that have thick ipsilateral relations with your area that origin. A final group the fibers room diffusely associated to the contralateral hemisphere. If over there is an analogy in the human brain with result reported in the animal literature, part neurons may cross the callosum and descend come the subcortical structures prior to terminating.

Fibers native different areas of the cortex overcome the callosum in discrete locations. To know this phenomenon, it is vital to examine the divisions of the corpus callosum (Fig. 1). The most anterior component of the callosum is the rostrum. Just behind the rostrum, the callosum bends to type the genu (or knee) and then extend posteriorly in the body. The body constricts contempt to come to be the isthmus and finally terminates in the contempt bulbous splenium. There is a an excellent deal of separation, personal, instance variation in the shape and also thickness that the various parts the the callosum. There have actually been attempts come understand distinctions in the anatomy that the right and left hemispheres and also in the lateralization of duty with regard come the morphology that the body callosum. As behavior claims regarding the contribute of different areas of the callosum become an ext precise, it will end up being more critical to be able to carefully specify the locations of the callosum in which specific fibers cross. Currently, however, the locations are conventionally characterized as proportions that the size of the callosum. There seems to it is in minimal distinction whether the curvature the the callosum is taken right into account or merely maximum anterior and posterior extension is offered for the partition. The anterior one-fourth that the callosum is taken into consideration the genu. The rostral body starts directly behind the genu, extending back to include the anterior one-third of the callosum. The facility one-third the the callosum is split into 2 equal sections, the anterior and also posterior midbody. The isthmus extends indigenous the posterior one-third come the posterior one-fifth of the callosum. Finally, the many posterior one-fifth is considered the splenium. Since these definitions are arbitrary, they might differ in information from investigator to investigator, depending upon the investigator's emphasis.


Generally, however, that is thought that the fibers that pass through the various regions that the corpus callosum represent the anterior-to-posterior company of the cerebral cortex (Fig. 2). Deepak Pandya and also Benjamin Seltzer prove an anterior-to-posterior organization of the callosal fibers of i in the rhesus monkey. Prefrontal cortex and also premotor cortex axons cross in the rostrum and also genu. Motor and also somatosensory axons are found primarily in the body. Auditory and also association locations are stood for in the isthmus and visual areas in the splenium. Stephen Lomber and colleagues document a similar arrangement in the corpus callosum of the cat, back auditory yarn are found throughout the body and also dorsal splenium, greatly overlapping through limbic and visual fibers except in the an extremely ventral part of the splenium, i beg your pardon are completely visual. The very same anterior-to-posterior organization has been prove by Marie Christine de Lacoste and colleagues in the person brain. That is, the right and left prefrontal, orbital–frontal, and also frontal language locations are connected in the rostrum and also the genu. The anterior part of the human body carries fibers from the sensory and motor regions that abut the main sulcus. It shows up that fibers from the area roughly the Sylvian fissure, linked with language duty in the left hemisphere, overcome in the posterior part of the body or isthmus. Finally, the splenium carries fibers connecting the visual locations of the occipital lobe.


*

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


Although the is now recognized that there space distinctive behavioral deficits linked with lesions come some areas of the callosum, contributions of the corpus callosum to behavior have no been simple to observe and understand. Some researchers have said that evolution evidence says that the body callosum plays a distinctive role in human behavior. The callosum is not existing in part primitive marsupials and also takes on considerably increased prestige in the human being species. The prominence of the body callosum shows up to boost as lateralization increases, but this partnership is currently an extremely speculative. In fact, James Rilling and also Thomas Insel controversy that, based on studies that 11 primate species, only the size of the splenium rises in proportion come increasing brain size, whereas the size of the body callosum as well as that the the anterior commissure space actually reduced relative to the size of other structures in greater primates. This observation suggests that any kind of changes in the callosum regarded human evolution are specific to details areas that the callosum such together the splenium.


Developmentally, the callosum is a little structure in the neonatal brain that rises in size and prominence as the yarn myelinate (Fig. 3). At approximately 7 mainly of gestation, the lamina terminalis starts to thicken forming the commissural plate. By about 9 main cells begin to type the massa commissurelis, which supports the development of the first commissural yarn at about 12 weeks. The an easy structure that the callosum is current by 20 weeks and also it proceeds to thicken and develop till birth, with breakthrough of the genu and also body arising before the of the splenium and rostrum. The myelinization of the corpus callosum is not believed to be finish until puberty, and recent evidence says that the reaches the maximum dimension at approximately age 25. It has actually been said that the distinctive evolutionary and also 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 knowledge developmental concerns of lateralization and hemispheric specialization. Deliniating that function has proven difficult.

See more: Watch Shaman King Episode 1 English Dubbed (English), Shaman King Original Series (English Dub) Blu


*

Figure 3. Relative size that the corpus callosum is seen in at 16 weeks (A), 40 weeks (B), and at adulthood (C) (adapted from S. P. Springer and also G. Deutsch, Left Brain, best Brain: Perspectives indigenous Cognitive Neuroscience. P. 260. Freeman, new York, 1997).