The corpus callosum is a white matter tract the connects the cerebral hemispheres, facilitating interhemispheric connectivity.
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From: The Neuroscience the Autism Spectrum Disorders, 2013
The corpus callosum is composed of millions of nerve yarn that attach the two halves that the brain. This fibers traveling with each other from one cerebral hemisphere to the other form a brain structure easily visible to the beginning student that neuroanatomy. Figure 1 shows a saggital ar of the brain, i beg your pardon is a slice that operation from front to ago on a upright plane. This slice passes with the midline. The huge curved framework in the middle of the mind is the body callosum.
Although there is substantial variability in the size and also shape that the corpus callosum in humans, the is known that it contains roughly 200 million yarn that lug neural signal from one next of the brain to the other. Although most of these fibers are thought to it is in excitatory, their impact may be inhibitory due to the task of inhibitory interneurons. Approximately half of this fibers are little and unmyelinated. These fibers transmit information an ext slowly 보다 the bigger myelinated axons, which are qualified of incredibly rapid transmission of information. Some of the fibers attach to similar areas in the right and also left hemispheres; various other fibers go to areas in the contralateral hemisphere that are analogous to locations that have dense ipsilateral connections with your area of origin. A last group that fibers space diffusely linked to the contralateral hemisphere. If over there is an analogy in the human brain with result reported in the animal literature, part neurons might cross the callosum and descend come the subcortical structures before terminating.
Fibers from different areas of the cortex overcome the callosum in discrete locations. To know this phenomenon, it is crucial to research the departments of the body callosum (Fig. 1). The many anterior component of the callosum is the rostrum. Just behind the rostrum, the callosum bends to kind the genu (or knee) and also then extend posteriorly in the body. The human body constricts slightly to end up being the isthmus and finally terminates in the contempt bulbous splenium. There is a good deal of individual variation in the shape and thickness of the various parts the the callosum. There have actually been attempts to understand distinctions in the anatomy of the right and also left hemispheres and in the lateralization of function with regard come the morphology that the corpus callosum. As behavioral claims concerning the contributions of different locations of the callosum become much more precise, the will end up being more crucial to have the ability to carefully define the areas of the callosum in which certain fibers cross. Currently, however, the areas are conventionally characterized as proportions that the length of the callosum. There appears to be minimal difference whether the curvature the the callosum is taken into account or merely maximum anterior and also posterior expansion is used for the partition. The anterior one-fourth the the callosum is thought about the genu. The rostral body starts directly behind the genu, extending back to include the anterior one-third that the callosum. The center one-third of the callosum is separation into two equal sections, the anterior and also posterior midbody. The isthmus extends indigenous the posterior one-third come the posterior one-fifth that the callosum. Finally, the most posterior one-fifth is taken into consideration the splenium. Due to the fact that these meanings are arbitrary, they might differ in detail from investigator to investigator, relying on the investigator's emphasis.
Generally, however, the is believed that the fibers the pass with the various regions of the body callosum represent the anterior-to-posterior company of the cerebral cortex (Fig. 2). Deepak Pandya and Benjamin Seltzer prove an anterior-to-posterior company of the callosal fibers of i in the rhesus monkey. Prefrontal cortex and premotor cortex axons overcome in the rostrum and also genu. Motor and somatosensory axons are found primarily in the body. Auditory and association locations are represented in the isthmus and also visual locations in the splenium. Stephen Lomber and colleagues document a similar arrangement in the corpus callosum the the cat, back auditory yarn are discovered throughout the body and also dorsal splenium, mainly overlapping through limbic and visual fibers except in the really ventral part of the splenium, i beg your pardon are totally visual. The same anterior-to-posterior organization has actually been demonstrated by Marie Christine de Lacoste and also colleagues in the human being brain. The is, the right and also left prefrontal, orbital–frontal, and frontal language locations are associated in the rostrum and also the genu. The anterior component of the human body carries yarn from the sensory and also motor regions that abut the main sulcus. It shows up that yarn from the area approximately the Sylvian fissure, linked with language role in the left hemisphere, overcome in the posterior component of the human body or isthmus. Finally, the splenium carries yarn connecting the visual locations of the occipital lobe.
Figure 2. Areas of the cortex where fibers that the corpus callosum originate are coded to complement the ar of the corpus callosum whereby those fibers overcome to the various other hemisphere (adapted indigenous M. C. DeLacoste, J. B. Kirkpatrick, and also A. D. Ross, Topography that the human being corpus callosum, J. Neuropathol. Exp. Neurol. 44, 578–591, 1985).
Although the is now known that there are distinctive behavior deficits associated with lesions to some areas of the callosum, contribute of the corpus callosum to actions have not been basic to observe and understand. Some researchers have said that evolution evidence argues that the body callosum theatre a distinctive role in human behavior. The callosum is not current in some primitive marsupials and takes on substantially increased prestige in the human species. The importance of the body callosum shows up to increase as lateralization increases, but this partnership is currently really speculative. In fact, James Rilling and Thomas Insel controversy that, based upon studies the 11 primate species, just the size of the splenium increases in proportion come increasing mind size, conversely, the size of the body callosum as well as that of the anterior commissure are actually reduced relative to the size of various other structures in higher primates. This observation suggests that any kind of changes in the callosum related to human development are specific to particular areas that the callosum such as the splenium.
Developmentally, the callosum is a tiny structure in the neonatal brain that rises in size and prominence as the fibers myelinate (Fig. 3). At around 7 weeks of gestation, the lamina terminalis starts to thicken creating the commissural plate. By approximately 9 main cells start to kind the massa commissurelis, which supports the growth of the an initial commissural yarn at roughly 12 weeks. The an easy structure the the callosum is present by 20 weeks and it proceeds to thicken and develop until birth, with advancement of the genu and also body occurring before that of the splenium and also rostrum. The myelinization that the body callosum is not thought to be finish until puberty, and also recent evidence argues that the reaches its maximum dimension at approximately age 25. It has been suggested that the distinctive evolutionary and developmental patterns suggest a special duty for the callosum in human being behavior. Sandra Witelson has said strongly that the anatomy the the callosum might be crucial to understanding developmental worries of lateralization and hemispheric specialization. Deliniating that role has proven difficult.
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Figure 3. Relative size of the body callosum is seen in at 16 weeks (A), 40 weeks (B), and at adulthood (C) (adapted native S. P. Springer and G. Deutsch, Left Brain, ideal Brain: Perspectives from Cognitive Neuroscience. P. 260. Freeman, brand-new York, 1997).