Most people are familiar with the concept of "left" and "right" brain dominance, and we know that the motor control on either side of the body comes from the opposite hemisphere. But I have read enough to know that "hemisphere dominance" is not quite as simple as what is commonly believed. Just because someone is left-handed does not mean that his or her personality and strengths are controlled by the right hemisphere, and vice versa for right-handers. The idea of being either creative, or better in math due to handedness should probably be considered an urban myth. In actuality, the human brain is more complicated than we can now understand. We know enough to realize that for any given action, both sides of the brain are put into play.
One area that does seem to be related to handedness is language, and I'll now give a brief overview of what is known about it.
Hemispheric Language in the Left-hander
About 70% of left-handers have language situated in the left hemisphere, while 95% of right-handers do. Also, about 15% of left-handers have speech controlled in the right hemisphere, and the remaining 15% show bilateral speech control. These figures were determined through tests done after anesthetisizing one or the other hemisphere (via the Wada test) to determine which controls speaking ability. The tests show that handedness is not a definite indicator of how one's brain is organized.
One theory put forth by Dr. Jerre Levy has it that hand posture when writing is correlated to which hemisphere the speech region (Broca's area) is located. These studies challenge the theory that hand position is dependent upon proper training and paper placement. Other studies, usually of stroke victims, have shown that some left-handers (predominantly females) have language skills more diffusely distributed over both hemispheres.
| Hemisphere where speech is located | |||
| Left | Right | ||
| Writing hand and position |
Left | inverted: pen used from above ("hooked") |
hand straight |
| Right | pen used under line; hand straight |
"hooked" | |
Curiouser and curiouser! Not all is as it first seems when it comes to handedness. But how many people are we talking about? The next section covers left-handedness in terms of how many, and how to quantify who is left-handed.
