In human beings, it is the left hemisphere that usually contains the specialized language areas. While this holds true for 97% of right-handed people, about 19% of left-handed people have their language areas in the right hemisphere and as many as 68% of them have some language abilities in both the left and the right hemisphere.
The
brain acts as "command central" for language and communication, controlling both physical and mental components of speech. Steps that trigger speech: Many areas of the brain work together to control speech, as illustrated. The specific regions used differ slightly for reading aloud or engaging in conversation. The visual cortex (1A) is engaged when reading aloud while the auditory cortex (1B) predominates during conversation. Image Credit: Zina Deretsky, National Science Foundation
The two hemispheres are thought to contribute to the processing and understanding of language: the left hemisphere processes the linguistic meaning of prosody (or, the rhythm, stress, and intonation of connected speech), while the right hemisphere processes the emotions conveyed by prosody. Studies of children have shown that if a child has damage to the left hemisphere, the child may develop language in the right hemisphere instead. The younger the child, the better the recovery. So, although the "natural" tendency is for language to develop on the left, human brains are capable of adapting to difficult circumstances, if the damage occurs early enough.
In the speaker (right), the brain controls all mental and physical aspects of speaking. Sounds begin as breath expelled from the lungs. On its journey to the mouth, the air vibrates as it is forced through the
vocal cords. The mouth, nose and tongue modify this vibrating air to form sound waves. Facial expressions and gestures also play a role in communication. In the listener (left), sound waves enter the ear and are then analyzed into words by the brain. Image Credit: Zina Deretsky, National Science Foundation
The first language area within the left hemisphere to be discovered is Broca's area, named after Paul Broca, who discovered the area while studying patients with aphasia, a language disorder. Broca's area doesn't just handle getting language out in a motor sense, though. It seems to be more generally involved in the ability to process grammar itself, at least the more complex aspects of grammar. For example, it handles distinguishing a sentence in passive form from a simpler subject-verb-object sentence — the difference between "The boy was hit by the girl" and "The girl hit the boy."
The second language area to be discovered is called Wernicke's area, after Carl Wernicke, a German neurologist who discovered the area while studying patients who had similar symptoms to Broca's area patients but damage to a different part of their brain. Wernicke's aphasia is the term for the disorder occurring upon damage to a patient's Wernicke's area.
Wernicke's aphasia does not only affect speech comprehension. People with Wernicke's aphasia also have difficulty recalling the names of objects, often responding with words that sound similar, or the names of related things, as if they are having a hard time recalling word associations.
Further Reading
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