Left vs. Right Brain
The idea that the left and right sides of the brain can control many different aspects of behavior in different categories is an interesting one. Four websites which consider this concept are Neuro Pearls, the American Speech-Language-Hearing Association website, Left vs. Right Brain Modes, and SPLITTING THE HUMAN BRAIN.
In Left Vs. Right Brain Modes, a direct comparison is presented in several categories. The left hemisphere is described as verbal, analytical, logical. The right hemisphere is nonverbal (responding to touch and music), intuitive, and sensory. In some ways the descriptions fit with the "left- handed artist" stereotype, such as the left hemisphere being factual, and the right brain responsive to color and shape. However, in other categories the "left handed artist" seems contradictory. For example, the left hemisphere (right-handedness) understands symbols and representations, while the right brain (left-handedness) is precise. As expected, the left hemisphere is identified with practicality and rationality, while the right hemisphere is emotional and originative.
This site also contains a list of behaviors in which each hemisphere is involved. It's still a bit surprising to match up those behaviors with handedness -it almost seems like having a palm reading!
So why does handedness occur in a ratio other than 50-50? Neuro Pearls, a web publication of the Dept. of Neurology at UT Southwestern, has an article titled "Handedness and Cerebral Dominance" by S. Clifford Schold, Jr, MD. He states that only 1 out of 10 people consider themselves left-handed or ambidextrous, and that for these people language function can be in either the left or the right hemisphere. There may be a genetic factor to handedness, as well as occurrence of brain injury. Not so common now is the pressure of society to be right-handed, and this explains people who are right-handed but still have speech function dominance from the right cerebral hemisphere. The presence of the language function in either hemisphere can be determined using the Wada test, in which a barbiturate is injected into an internal carotid artery and the effects upon language are observed.
It is still unknown why handedness and language dominance are related in the brain, or why language is not bilateral.
The American Speech-Language-Hearing Association (ASHA)s website contains the article "Language: Left Brain? Right Brain? Both?" which describes the history of discovering the two hemispheres have different duties to the body, especially in terms of handedness and speech. Damage to the left side of the brain in most of Dr. Marc Dax's patients caused a loss of speech (1836). After his death, many more similar reports were recorded.
Much later, the right hemisphere was found to control essential functions as well. Since the effects of right hemisphere damage are more subtle, as seen in the first website, this conclusion took much longer to...