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History Scientists 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 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 (Springer, S. P., & Deutsch, G. (1997). Left Brain Right Brain: Perspectives from Cognitive Neuroscience (5th ed.). New York: W.H. Freeman and Company.). Gall’s theories were not popular among most scientists at the time, and it was not until 1861

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 (Toga, A. W., & Thompson, P. M. (2003). Mapping brain asymmetry. Nature Reviews Neuroscience, 4, 37. Retrieved from https://doi.org/10.1038/nrn1009 ).

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, 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 (Lewis, D. W., & Diamond, M. C. (1995). The Influence of Gonadal Steroids on the Asymmetry of the Cerebral Cortex. In R. J. Davidson & K. Hugdahl (Eds.), Brain Asymmetry(pp. 31–50). Cambridge, Massachusetts: The MIT Press.). And work with zebrafish

Current Research on Brain Asymmetry Lateralization of function and asymmetry in the human brain is a continuously 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 differences that occur during different life stages (Toga, A. W., & Thompson, P. M. (2003). Mapping brain asymmetry. Nature Reviews Neuroscience, 4, 37. Retrieved from https://doi.org/10.1038/nrn1009 ). 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 (Aida Gómez-Robles, William D. Hopkins, and Chet C. Sherwood. Increased morphological asymmetry, evolvability and plasticity in human brain evolution. 280. Proceedings of the Royal Society B: Biological Sciences. http://doi.org/10.1098/rspb.2013.0575 ).

Continued study of brain asymmetry also contributes to the understanding and treatment of complex diseases. Alzheimer’s disease, for example, …

As has been the case in the past, studies on language and the implications of left- and right- handedness also dominate current research on brain asymmetry.

Outline for article on Brain Asymmetry:

I. Introduction -- what is brain asymmetry and why is it significant


 * Distinction between neuroanatomical differences of right and left sides and lateralized functional differences (to be expanded upon further down)

II. Background [COURTNEY]


 * Scientists/Researchers who have contributed to understanding brain asymmetry
 * Localization: Flourens, Broca, Wernicke
 * 1870s Germans: dogs, electro-stimulation
 * Brain asymmetry in other species; brain asymmetry in mammals (brief)
 * zebrafish

III. Brain asymmetry in humans [FATU]


 * Neuroanatomical differences between the left and right sides of the brain
 * Significant regions in each side of the brain and their functions
 * Lateralized functional differences: lateralization of brain function
 * Conditions associated with damage to one side or the other

IV. Current Research on Brain Asymmetry [COURTNEY]