The Rise of Localization
The introduction of localization was not an easy task, however, an important one. The most stifling reasons for the early rejection of localization came from the philosophers of the time being more popular (Karenberg, 2009). Karl Lashley, although he came after the initial wave of localization, had come up with the concept of mass action which basically says that it isn’t a matter of what region of the brain is destroyed but simply how much that affects behavior and functioning (Posner & DiGirolamo, 2000). He found that it didn’t matter what part of the brain was destroyed in his animal subjects, but how much which changed behavioral functioning (Posner & DiGirolamo, 2000). “Destruction of any part of the cortex produces a partial loss of the habit and equal amounts of destruction produce equal amounts of loss, regardless of locus within the cortex” (Lashley, 1930, “Dynamic Aspects of Localization,” para 2). To illustrate this further, if someone were to have their frontal cortex removed, these theorists would believe that it would haven been comparable to removing the same amount from the occipital lobe as far as the deficits seen. It is easy to see now how this was not indicative of how later scientist thought the brain worked.
The first hint of localization came in the form of a theory by Charles Bell about the function of neurons in the spine. Charles Bell (as cited in Steinberg, 2009) found that the roots on the front (anterior) of the spinal cord produced movement when stimulated by electricity but the ones on the outside (posterior) did not. Then shortly after, François Magendie (as cited in Steinberg, 2009) found that when one cuts the posterior roots, it causes a lack of sensory information sent to the brain while cutting the anterior results in the animal to be paralyzed. This was known as the Bell-Magendie Hypothesis (Steinberg, 2009). This theory was established in 1811 and is where localization truly began (Finger & Wade, 2002a). The reason why this is all important is because it shows that there are separate functions for certain parts of the nervous system. The early theories would have found both of these cuts to be the same in outcome, which they are, here, clearly not.
Following on the back of this theory regarding functions of nerves by Charles Bell, in 1826, Johannes Müller came up with his theory regarding “specific nerve energies” ( Finger & Wade, 2002b, p.235). The basic notion of this was that neurons do not create an exact conceptualization of the external world but simply that firing of those neurons by manner of any stimulus that can stimulate them are responsible for what gives rise to the phenomena (Finger & Wade, 2002b). “Similarly, no matter how the optic nerve is stimulated, whether by light, electricity, or pressure, the phenomenological experience will be visual – not auditory, olfactory, tactual, or gustatory” (Finger & Wade, 2002b, p235). This is important because it allowed for a new conceptualization for the functions of the brain to take place as centers of processing these simple items rather than a center for already processed information.
It is worth mentioning, even if only as to show the attempted progression toward the idea of localization, the work of Franz Gall. His perspective of the brain, known as Phrenology, consisted of each individual part of the brain being responsible for their respective functions in the creation of consciousness (York, 2009). However, this idea eventually came to be known as false by the 1850s (York, 2009). Despite its failure, localization was not a loss cause.
Without the discovery of localization, neuroscience could have not have stepped forward as a discipline. John Hughlings Jackson, a physician who practiced in London in the late 19th century, is credited with the discovery of cerebral localization (Steinberg, 2009). In 1864, Hughlings Jackson began to formulate a viable method for studying the functions of the brain by studying the symptoms of diseases and the part of the nervous system effected (Steinberg, 2009). Basically, what this entails is discovering what parts are used for what by examining what happens to behavior when those parts are disrupted. Through this method, which was maintained for quite a lot of significant studies, it can be understood how examination of the brain proceeded.
Later, less drastic measures were taken to understand brain functions. With the inception of imaging techniques, brain activity can more easily be seen and therefore we can better localize specific functions within the brain (Posner & DiGirolamo, 2000). “The development first of computerized axial tomography and later positron emission tomography and, most recently, functional magnetic resonance imagine provided, for the first time, direct access to functioning of the intact living human brain” (Cowan, Harter, & Kandel, 2000, p.351). However, there still seems to be a lack of accuracy that comes along with non-invasive neural imaging which cannot compete with electrodes (Posner & DiGirolamo, 2000). Around the 1970s, it was becoming possible to study the role of neurons without having to lesion them (Cowan, Harter, & Kandel, 2000). Ed Evarts was the first to study the activity of individual neurons using electrodes while monkeys were awake to determine functions within the cerebral cortex (Cowan, Harter, & Kandel, 2000). With the introduction of new types of brain imaging, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), old notions, such as Broca’s area, have been challenged (Bookheimer, 2002). Possibly, Broca’s area could be a combination of simple neurons which give rise to language as well as other tasks not specific to language (Bookheimer, 2002). Imaging has allowed for a more encompassing view of the brain which postmortem examinations could not.
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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