Discoveries from Ablation and Lesions
It is kind of hard to talk about neuroscience without discussing ablation and lesions. There has been a lot gained from both intentional and accidental ablation over the years which has led to better understanding of the localization of function in the brain. Here, a few will be named which seem to be most prominent in the study of the brain and how it works.
One of the most important discoveries due to ablation was by Pierre Paul Broca. In 1863, Paul Broca discovered that lesions in the left frontal cortex produced deficiencies in language production and thus began the method of lesion study for the discovery of specific brain area functions (Cowan, Harter, & Kandel, 2000). Broca (1861) writes notes about his patient, Tan, who when given an autopsy after death was shown to have deterioration in the left front hemisphere, the place known as Broca’s area. John Hughlings Jackson (as cited in York, 2009) didn’t exactly agree with the localization of language to this area but rather felt that there were different levels of language which are deteriorated as the area is deteriorated. Hughlings Jackson believed in “the sensorimotor machine,” which described the nervous systems as “restricted solely to sensation and movement” (Steinberg, 2009, p255). Through this, he believed that higher regions of function were supposed to mediate and inhibit the simpler regions (York, 2009). More importantly however, with this discovery, Broca established that there was less of a place for the concepts of mass action or equipotentiality because this had significantly supported localization of function (York, 2009). It was Broca’s approach to understanding the human brain that allowed for the most insight into its inner-workings until the creation of imaging techniques later on (Cowan, Harter, & Kandel, 2000).
(purepedantry, 2007, September 18)
It is difficult to talk about Paul Broca without also discussing Carl Wernicke. Wernicke (as cited in York, 2009) found areas of damage which correlated to the understanding of language, the flip-side to Broca’s aphasia, and put forth a theory for the connection between the two areas. This understanding of the language areas of the brain allowed for more discoveries in which mediation between two locations gave rise to cognitive processes.
(cogmonaut, 2010, Janurary 26)
Surprisingly, World War I had a significant effect, due to the amount of lesions created during that time from the war, on the entire realm of science by slowing the conceptualization of reductionist localization back down to a controversy with Gestalt localization theory (York, 2009). Von Monakow postulated that because his patients could recover their ability to function overtime, then there was something more than just simple localization (York, 2009). “Instead he attributed recovery to the resolution of a particular type of neuronal inhibition that he called diaschisis” (York, 2009, p.287). In 1926 though, Henry Head put the final nail in the coffin of the holistic thought and laid the last brick for the theory of localization with his Apashia and Kindred Disorders of Speech which basically put forth the idea already hinted at that if this type of processing could be localized to a specific area in the brain, then anything can also be (York, 2009).
The first corpus callosotomy, or cutting of the corpus callosum, was performed in 1939 by Van Wagenen and Herren (Devinsky & Laff, 2003). In 1961, studies were performed by Geschwind and Kaplan on the effects of a cutting of the corpus callosum (York, 2009). That year, Kaplan performed such a procedure and found remarkable symptoms resulting from it (Devinsky & Laff, 2003). The patients writing skills were intact when writing with his right hand but were severely impaired with his left which was more pronounced than the effects of simply writing with a non-dominant hand would produce (Devinsky & Laff, 2003). They took this a step further by having him identify objects using only either his left or right hand and found that the right hand was able to identify these objects but the left could not (Devinsky & Laff, 2003). Severing the corpus callosum affected neither the personality attributes of individuals nor the ability to learn new tasks (Devinsky & Laff, 2003). Research from this type of surgery allowed for better understanding of the hemispheric functions.
Individuals with severed corpus callossums will find that skills that they had previously learned should still be intact while new behaviors may be a bit more difficult to learn, but not restricted (Devinsky & Laff, 2003).
(Neuroslicer, 2007, April 18)
Phineas Gage is probably the most famous story regarding localization of function. Harlow (as cited in Cowan, Harter, & Kandel, 2000), discusses him as a railroad worker, who after a rail had been propelled through his skull and frontal cortex, his personality was severely changed forever. This case lead to many studies with animals to discover that this was the center of planning and decision making (Cowan, Harter, & Kandel, 2000).
Broca, P.P. (1861). Loss of speech, chronic softening and partial destruction of the anterior left lobe of the brain. Bulletin de la Société Anthroplogique, 2, 235 – 238. Trans. Green, C.D. (2003). Retrieved from: http://psychclassics,yorku.ca/Broca/perte-e.htm
cogmonaut (2010, January 26). Wernicke’s apashia [Video File]. Retrieved from: http://www.youtube.com/watch?v=dKTdMV6cOZw
Cowan, W.M., Harter, D.H. & Kandel, E.R. (2000). The emergence of modern neuroscience: Some implications for neurology and psychiatry. Annual Review of Neuroscience, 23, 343 – 391. doi: 10.1146/annurev.neuro.23.1.343
Devinsky, O. & Laff, R. (2003). Callosal lesions and behavior: History and modern concepts. Epilepsy & Behavior, 4(6), 607 – 617. doi: 10.1016/j.yebeh.2003.08.029
Neuroslicer (2007, April 18). Split brain behavioral experiments [Video File]. Retrieved from: http://www.youtube.com/watch?v=ZMLzP1VCANo
purepedantry (2007, September 18). Broca’s aphasia [Video file]. Retrieved from: http://www.youtube.com/watch?v=f2IiMEbMnPM
Steinberg, D.A. (2009). Cerebral localization in nineteenth century – the birth of a science and its modern consequences. Journal of the History of the Neurosciences, 18, 254 – 261. doi: 10.1080/09647040802025326
vaXzine (2008, February 19). Left-brain-right-brain [Image File]. Retrieved from: http://www.flickr.com/photos/vaxzine/2278300537/
York, G.K. III (2009). Localization of language function in the twentieth century. Journal of the History of the Neurosciences, 18, 283 – 290. doi: 10.1080/09647040802025979
By Travis Bice