Psychologists have found that the brain often shows “localization of function”. This means that different parts of the brain carry out different tasks, for example, vision, voluntary movement and speech. The idea is that not all parts of the brain do the same thing, and that each part functions on its own, without the aid of other areas of the brain. This may seem obvious, but other organs, such as the liver, do not show localization of function; one part of the liver does the same thing as a part on the opposite side.
A famous example of brain localization is the case of Phineas Gage; a railway worker in 1848, who one day, while trying to blow out a hole in the side of a mountain, had a metal rod shoot through his cheek, into his brain, and out the top of his head, landing over 100 meters away. The pole took with it a substantial amount of Gage’s brain, but surprisingly enough he was awake and mobile throughout the experience, even able to sit up and ride to the nearest hospital and wait for a doctor to examine him. After his examination, Dr Harlow came to the conclusion that Gage was fine. This shocked many people, as brain localization had not yet been studied, and at the time the idea of a man loosing part of his brain and still being able to function was outrageous. It was only a few weeks later that Phineas’s friends and family began to notice significant changes in his personality and his moods; he had become inappropriate, rude, impulsive and irritable. The longitudinal study of his brain showed damage to his frontal lobe, an area of the brain that is now known to affect personality and social behavior. This case study opened up the floor for other psychologists to further study the idea of brain localization. This change in personality and mood never reversed to its normal state, which shows that another area of the brain did not take over the role of the damaged frontal lobe in balancing Gage’s personality and mood
References: http://pd.scisdragons.net/ibpsych/2011/09/04/localization-of-brain-function-4/ http://viper.eng.iastate.edu/ncseminar/presentations/week5.pdf http://www.guardian.co.uk/science/2009/apr/07/brain-neuroscience-stroke-depression