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are not? What if it’s like comparing apples to oranges? This assumption is critical to test if, for example, one wants to make inferences between patient HOW THE BRAIN HANDLES A populations and healthy controls, who MISSING BODY PART may have differences in overall B Y K A RT I K P R A D E E PA N activity. Arbuckle and his colleagues aimed to make sure that this assumption is a reasonable one to make. To do this, they looked at the brain n the 1990s, V.S. Ramachandran activity patterns of people pressing released a series of experiments that buttons. described a phenomenon whereby, despite Arbuckle explains it as such: when you a limb being amputated, a number of move one finger, you have a certain patients continued to vividly experience pattern of activity in the motor cortex in the presence of that limb – a phantom the brain. These patterns are largely sensation. This phantom sensation would unique to each finger. If you move the often occur as a phantom pain, whereby same finger twice within the same excruciating sensation would feel like it’s time-frame, the overall activity coming from the body part that is no increases, but ideally the same longer there. fine-grained activity pattern is still present. Therefore, if the assumption This experiment lent itself to the idea of about the stability of fMRI activity widespread reorganization of the sensory patterns is valid, you would expect to see circuits of the brain, even after adulthood. similar patterns for the same finger early and even current whether it was pressed at slow speeds or Many neuroscientists believe that our perception fast speeds. of touch originates from a topographical Through a series of analyses, they found map of our body parts in the brain. Much that the patterns of the finger presses like a map that tells you where restaurants, were measurably quite stable as the schools, hospitals are in the city, the pressing speed increased. This provides topographical maps inform us where the strong evidence in support of this feelings of hunger or control of hand assumption. This is good news for a movements are located in the brain. When large body of studies and analysis visualized, it creates a distorted approaches that rely on measuring brain human-like representation of our lips, feet, hands, etc. on the surface of the brain, patterns for their fMRI analysis. called a homunculus. “We are a bit more confident,” Arbuckle says. “We think that these Accordingly, when a limb undergoes an representations actually, truly do amputation, adjacent areas are believed to represent something meaningful and take over the now missing-limb representation, thus changing the informative.” organization of the homunculus. In other words, the brain real-estate previously
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