Editing Split-brain (section)

=== Role of the corpus callosum ===
[[File:Corpus callosum.gif|thumb|The [[corpus callosum]], highlighted in red, is the main neural pathway between the two hemispheres.]]
The corpus callosum is a structure in the brain along the [[longitudinal fissure]] that facilitates much of the communication between the two hemispheres. This structure is composed of [[white matter]]: millions of [[axon]]s that have their [[dendrite]]s and [[terminal bouton]]s projecting in both the right and left hemisphere. However, there is evidence that the corpus callosum may also have some inhibitory functions.<ref>{{cite journal | last = O'Shea |first=R. P. | year = 2003 | title = Binocular rivalry in split-brain observers | journal = Journal of Vision | volume = 3 | issue = 10| pages = 610–615 | doi=10.1167/3.10.3| pmid = 14640884 | doi-access = free }}</ref> Post-mortem research on human and monkey brains shows that the corpus callosum is functionally organized.<ref>{{cite journal|last=Mooshagian|first=Eric|title=Anatomy of the Corpus Callosum reveals its Function|journal=Journal of Neuroscience|year=2008|volume=28|issue=7|pages=1535–1536| pmc=6671538|  doi=10.1523/JNEUROSCI.5426-07.2008|pmid=18272674|doi-access=free}}</ref> This organization results in modality-specific regions of the corpus callosum that are responsible for the transfer of different types of information. Research has revealed that the anterior midbody transfers motor information, the posterior midbody transfers somatosensory information, the isthmus transfers auditory information, and the splenium transfers visual information.<ref>{{cite journal |vauthors=Risse GL, Gates J, Lund G, Maxwell R, Rubens A | year = 1989 | title = Inter-hemispheric transfer in patients with incomplete section of the corpus callosum: anatomic verification with magnetic resonance imaging | journal = Archives of Neurology | volume = 46 | issue = 4| pages = 437–443 | doi=10.1001/archneur.1989.00520400097026| pmid = 2705905 }}</ref> Although much of the inter-hemispheric transfer occurs at the corpus callosum, there are trace amounts of transfer via commissural pathways, such as the anterior commissure, posterior commissure, habenular commissure, and the hippocampal commissure'''.'''<ref>{{Cite web |title=Commissural pathways |url=https://www.kenhub.com/en/library/anatomy/commissural-pathways |access-date=2023-11-16 |website=Kenhub |language=en}}</ref>

Studies of the effects on the visual pathway on split-brained patients has revealed that there is a redundancy gain (the ability of target detection to benefit from multiple copies of the target) in simple reaction time. In a simple response to visual stimuli, split-brained patients experience a faster reaction time to bilateral stimuli than predicted by model.<ref>{{cite journal |last1=Corballis |first1=M. C. |last2=Corballis |first2=P. M. |last3=Fabri |first3=M. | year = 2003 | title = Redundancy gain in simple reaction time following partial and complete callosotomy | journal = Neuropsychologia | volume = 42 |issue=1 | pages = 71–81 | doi=10.1016/s0028-3932(03)00152-0|pmid=14615077 |citeseerx=10.1.1.503.8952 |s2cid=45852555 }}</ref> A model proposed by Iacoboni et al.<ref>{{cite journal |last1=Iacoboni |first1=M. |last2=Fried |first2=I. |last3=Zaidel |first3=E. | year = 1994 | title = Callosal transmission time before and after partial commissurotomy | journal = NeuroReport | volume = 5 | issue = 18| pages = 2521–2524 | doi=10.1097/00001756-199412000-00029|pmid=7696594 }}</ref> suggests split-brained patients experience asynchronous activity that causes a stronger signal, and thus a decreased reaction time. Iacoboni also suggests there exists dual attention in split-brained patients, which implies that each cerebral hemisphere has its own attentional system.<ref>{{cite journal |last1=Arguin |first1=M. |last2=Lassonde |first2=M. |last3=Quattrini |first3=A. |last4=Del Pesce |first4=M. |last5=Foschi |first5=N. |last6=Papo |first6=I. | year = 2000 | title = Divided visuo-spatial attention systems with total and anterior callosotomy | journal = Neuropsychologia | volume = 38 | issue = 3| pages = 283–291 | doi=10.1016/s0028-3932(99)00077-9|pmid=10678694 |s2cid=23798895 }}</ref> An alternative approach taken by Reuter-Lorenz et al.<ref>{{cite journal |last1=Reuter-Lorenz |first1=P. A. |last2=Nozawa |first2=G. |last3=Gazzaniga |first3=M. S. |last4=Hughes |first4=H. C. | year = 1995 | title = Fate of neglected targets: a chronometric analysis of redundant target effects in the bisected brain | journal = Journal of Experimental Psychology: Human Perception and Performance | volume = 21 | issue = 2| pages = 211–230 | doi=10.1037/0096-1523.21.2.211|pmid=7714469 }}</ref> suggests that enhanced redundancy gain in the split brain is primarily due to a slowing of responses to unilateral stimuli, rather than a speeding of responses to bilateral ones.

The simple reaction time in split-brained patients, even with enhanced redundancy gain, is slower than the reaction time of normal adults.{{citation needed|date=December 2020}}