| 词条 | Brain asymmetry |
| 释义 |
In human neuroanatomy, brain asymmetry can refer to at least two quite distinct findings:
Neuroanatomical differences themselves exist on different scales, from neuronal densities, to the size of regions such as the planum temporale, to—at the largest scale—the torsion or "wind" in the human brain, reflected shape of the skull, which reflects a backward (posterior) protrusion of the left occipital bone and a forward (anterior) protrusion of the right frontal bone.[1] In addition to gross size differences, both neurochemical and structural differences have been found between the hemispheres. Asymmetries appear in the spacing of cortical columns, as well as dendritic structure and complexity. Larger cell sizes are also found in layer III of Broca's area. The human brain has an overall leftward posterior and rightward anterior asymmetry (or brain torque). There are particularly large asymmetries in the frontal, temporal and occipital lobes, which increase in asymmetry in the antero-posterior direction beginning at the central region. Leftward asymmetry can be seen in the Heschl gyrus, parietal operculum, Silvian fissure, left cingulate gyrus, temporo-parietal region and planum temporale. Rightward asymmetry can be seen in the right central sulcus (potentially suggesting increased connectivity between motor and somatosensory cortices in the left side of the brain), lateral ventricle, entorhinal cortex, amygdala and temporo-parieto-occipital area. Sex-dependent brain asymmetries are also common. For example, human male brains are more asymmetrically lateralized than those of females. However, gene expression studies done by Hawrylycz and colleagues and Pletikos and colleagues, were not able to detect asymmetry between the hemispheres on the population level.[2][3] HistoryScientists first began to make discoveries regarding lateralization of the brain, or differences in anatomy and corresponding function between the brain’s two hemispheres, in the mid-19th century. Franz Gall, a German anatomist, was the first to describe what is now known as the Doctrine of Cerebral Localization. Gall believed that, rather than the brain operating as a single, whole entity, different mental functions could be attributed to different parts of the brain. He was also the first to suggest language processing happened in the frontal lobes.[4] Gall’s theories were controversial among many scientists at the time. In 1861, however, surgeon Paul Broca provided evidence that supported Gall’s theories. Broca discovered that two of his patients who had suffered from speech loss had similar lesions in the same area of the left frontal lobe.[4] While this was compelling evidence for localization of function, the connection to “sidedness” was not made immediately. As Broca continued to study similar patients, he made the connection that all of the cases involved damage to the left hemisphere, and in 1864 noted the importance of these findings. He also (incorrectly) proposed theories about the relationship of speech areas to “handedness”. Accordingly, some of the most famous early studies on brain asymmetry involved speech processing. Asymmetry in the Sylvian Fissure (also known as the lateral sulcus), which separates the frontal and parietal lobes from the temporal lobe, was one of the first incongruencies to be discovered. Its anatomical variances are related to the size and location of two areas of the human brain that are important for language processing, Broca’s area and Wernicke's Area, both in the left hemisphere.[5] Around the same time that Broca and Wernicke made their discoveries, neurologist Hughlings Jackson suggested the idea of a “leading hemisphere”, which would eventually pave the way for understanding hemispheric “dominance” for various processes. Several years later, in the mid-20th century, critical understanding of hemispheric lateralization for visuospatial, attention and perception, auditory, linguistic and emotional processing came from patients who underwent split-brain procedures to treat disorders such as epilepsy. In split-brain patients, the corpus callosum is cut, severing the main structure for communication between the two hemispheres. The first modern split-brain patient was a war veteran known as W.J.[6] Brain asymmetry is not unique to humans. In addition to studies on human patients with various diseases of the brain, much of what is understood today about asymmetries and lateralization of function has been learned through both invertebrate and vertebrate animal models, including zebrafish, pigeons, rats, and many others. For example, more recent studies revealing sexual dimorphism in brain asymmetries in the cerebral cortex and hypothalamus of rats show that sex differences emerging from hormonal signaling can be an important influence on brain structure and function.[7] Work with zebrafish has been especially informative because this species provides the best model for directly linking asymmetric gene expression with asymmetric morphology, and for behavioral analyses.[8] Brain Asymmetry in Humans{{Empty section|date=March 2019}}Current Research on Brain AsymmetryLateralization of function and asymmetry in the human brain continues to propel a popular branch of neuroscientific and psychological inquiry. Technological advancements for brain mapping have enabled researchers to see more parts of the brain more clearly, which has illuminated previously undetected lateralization differences that occur during different life stages.[5] As more information emerges, researchers are finding insights into how and why early human brains may have evolved the way that they did to adapt to social, environmental and pathological changes. This information provides clues regarding plasticity, or how different parts of the brain can sometimes be recruited for different functions.[9] Continued study of brain asymmetry also contributes to the understanding and treatment of complex diseases. Neuroimaging in patients with Alzheimer’s disease, for example, shows significant deterioration in the left hemisphere, along with a rightward hemispheric dominance—which could relate to recruitment of resources to that side of the brain in the face of damage to the left.[10] These hemispheric changes have been connected to performance on memory tasks.[11] As has been the case in the past, studies on language processing and the implications of left- and right- handedness also dominate current research on brain asymmetry. See also
References1. ^{{cite journal | vauthors = LeMay M | title = Asymmetries of the skull and handedness. Phrenology revisited | journal = Journal of the Neurological Sciences | volume = 32 | issue = 2 | pages = 243–53 | date = June 1977 | pmid = 874523 | doi = 10.1016/0022-510X(77)90239-8 }} 2. ^{{cite journal | vauthors = Hawrylycz MJ, Lein ES, Guillozet-Bongaarts AL, Shen EH, Ng L, Miller JA, van de Lagemaat LN, Smith KA, Ebbert A, Riley ZL, Abajian C, Beckmann CF, Bernard A, Bertagnolli D, Boe AF, Cartagena PM, Chakravarty MM, Chapin M, Chong J, Dalley RA, David Daly B, Dang C, Datta S, Dee N, Dolbeare TA, Faber V, Feng D, Fowler DR, Goldy J, Gregor BW, Haradon Z, Haynor DR, Hohmann JG, Horvath S, Howard RE, Jeromin A, Jochim JM, Kinnunen M, Lau C, Lazarz ET, Lee C, Lemon TA, Li L, Li Y, Morris JA, Overly CC, Parker PD, Parry SE, Reding M, Royall JJ, Schulkin J, Sequeira PA, Slaughterbeck CR, Smith SC, Sodt AJ, Sunkin SM, Swanson BE, Vawter MP, Williams D, Wohnoutka P, Zielke HR, Geschwind DH, Hof PR, Smith SM, Koch C, Grant SG, Jones AR | display-authors = 6 | title = An anatomically comprehensive atlas of the adult human brain transcriptome | journal = Nature | volume = 489 | issue = 7416 | pages = 391–399 | date = September 2012 | pmid = 22996553 | pmc = 4243026 | doi = 10.1038/nature11405 }} 3. ^{{cite journal | vauthors = Pletikos M, Sousa AM, Sedmak G, Meyer KA, Zhu Y, Cheng F, Li M, Kawasawa YI, Sestan N | title = Temporal specification and bilaterality of human neocortical topographic gene expression | journal = Neuron | volume = 81 | issue = 2 | pages = 321–32 | date = January 2014 | pmid = 24373884 | pmc = 3931000 | doi = 10.1016/j.neuron.2013.11.018 }} 4. ^1 {{Cite book |title=Left Brain Right Brain: Perspectives from Cognitive Neuroscience |last=Springer |first=Sally |last2=Deutsch |first2=Georg | name-list-format = vanc |publisher=W.H. Freeman & Company |year=1997 |isbn= |location=New York |pages= }} 5. ^1 {{cite journal | vauthors = Toga AW, Thompson PM | title = Mapping brain asymmetry | journal = Nature Reviews. Neuroscience | volume = 4 | issue = 1 | pages = 37–48 | date = January 2003 | pmid = 12511860 | doi = 10.1038/nrn1009 }} 6. ^{{Cite book | first1 = Michael S | last1 = Gazzaniga | first2 = Richard B | last2 = Ivry | first3 = G R | last3 = Mangun | name-list-format = vanc |title=Cognitive neuroscience : the biology of the mind |publisher=Norton |year=2002 |isbn=978-0393977776 |edition=2nd |location=New York |pages= |chapter=Cerebral Lateralization and Specialization |oclc=47767271}} 7. ^{{Cite book|title=Brain asymmetry| vauthors = Lewis DW, Diamond MC |publisher=MIT Press|others=|year=1995|isbn=978-0585326634| veditors = Davidson R, Hugdahl K |edition=2nd print|location=Cambridge, Mass.|pages=31–50|chapter=The Influence of Gonadal Steroids on the Asymmetry of the Cerebral Cortex|oclc=45844419}} 8. ^{{cite journal | vauthors = Concha ML | title = The dorsal diencephalic conduction system of zebrafish as a model of vertebrate brain lateralisation | journal = NeuroReport | volume = 15 | issue = 12 | pages = 1843–6 | date = August 2004 | pmid = 15305121 | pmc = 1350661 | doi = 10.1097/00001756-200408260-00001 }} 9. ^{{cite journal | vauthors = Gómez-Robles A, Hopkins WD, Sherwood CC | title = Increased morphological asymmetry, evolvability and plasticity in human brain evolution | journal = Proceedings. Biological Sciences | volume = 280 | issue = 1761 | pages = 20130575 | date = June 2013 | pmid = 23615289 | pmc = 3652445 | doi = 10.1098/rspb.2013.0575 }} 10. ^{{cite journal | vauthors = Liu H, Zhang L, Xi Q, Zhao X, Wang F, Wang X, Men W, Lin Q | title = Changes in Brain Lateralization in Patients with Mild Cognitive Impairment and Alzheimer's Disease: A Resting-State Functional Magnetic Resonance Study from Alzheimer's Disease Neuroimaging Initiative | language = English | journal = Frontiers in Neurology | volume = 9 | pages = 3 | date = 2018 | pmid = 29472886 | pmc = 5810419 | doi = 10.3389/fneur.2018.00003 }} 11. ^{{cite journal | vauthors = Yang C, Zhong S, Zhou X, Wei L, Wang L, Nie S | title = The Abnormality of Topological Asymmetry between Hemispheric Brain White Matter Networks in Alzheimer's Disease and Mild Cognitive Impairment | language = English | journal = Frontiers in Aging Neuroscience | volume = 9 | pages = 261 | date = 2017 | pmid = 28824422 | pmc = 5545578 | doi = 10.3389/fnagi.2017.00261 }} Further reading{{refbegin}}
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