Question

Consistency and specificity of brain function imply localization of function. How has this concept evolved and to what extent are functions localized in the brain ?

Answer 1

The left and right hemispheres of the brain may seem like mirror images of each other superficially, however, they are very different in their functioning which is known as lateralization of functions. The two hemispheres perform different functions and together they are capable of executing complex actions. Corpus Callosum, is a band of nerve fibers which connects the two hemispheres of the brain. It passes between the two hemispheres, through which they communicate. If the Corpus Callosum is cut there's no communication between the two hemispheres.

Assuming that the two hemispheres are no longer connected, and the subject is seated with a special set of glasses and is presented with a visual stimulus on the right visual field which is a picture of a baseball, then, he is verbally going to answer what he sees. The response made by him is that he sees a baseball. The way our visual system is constructed, the right visual field stimulates the left hemisphere, which controls speech. Thus, he was able to answer what he could see, verbally. Also considering if a picture of violin is flashed to the same subject on the left visual field, the subject would not be able to name it. He would instead mimic what he sees through actions or gestures but he would not be able to name it. The left visual field stimulates the right hemisphere, which controls our motor activities. This is the reason why both the hemispheres cannot be severed. They need to communicate with each other for a person to perform functions normally. If they were not severed, the subject would have answered what he sees on the screen, a baseball and a violin.