As adults we speak an average of 15,000 words a day. An average person will speak 370 million words in their lifetime. Each word we speak is only achieved through a complex pathway involving the brain, nerves, and muscles. Scientist have found two areas in the brain that specialize in the miracle of speech. These two areas are called Broca’s area and Wernicke’s area.
Broca’s Area
Broca’s area was discovered in the 1800’s by French neurologist Paul Broca. Broca discovered the area while conducting autopsies on two of his patients who had difficulty speaking, he recognized that an area in the inferior frontal gyrus of the frontal lobe appeared damaged in both patients. The area is responsible for the motor control of speech. Meaning that it allows the tongue, lips, and vocal cords to move in extremely precise ways to produce the words we wish to say. Scientists have also discovered that the area is also responsible for some language comprehension, grammar in specific. If damage is done to Broca’s area the patient is diagnosed with Broca’s Aphasia. Aphasia is a difficulty in speaking, and Broca’s aphasia is a difficulty in producing words due to trouble in coordinating the muscles of the tongue, lips, and vocal cords. People with Broca’s Aphasia find little difficulty in understanding what somebody is saying. Their only problem with language comprehension is understanding some of the grammatical concepts in what is being said.
However, the brain is adaptable hence if someone has damage done to Broca’s area the brain can find another place nearby to replace its function.
Wernicke’s Area
Also discovered in the 1800’s using the same method as Broca, an autopsy on a patient. However, Wernicke’s patient’s problem wasn’t that he was incapable of speaking, but was that he was incapable of understanding what was being said to him. When wanting to say something, a person with damage in this area, would answer with what is called a “word salad” which are just random words some with no meaning at all. This is called Wernicke’s aphasia.
Wernicke’s area is found on the superior temporal gyrus of the temporal lobe.
Arcuate Fascilicus
The arcuate fascilicus is what connects wernicke’s area with broca’s area. It is a nerve tract that when damaged also causes a specific aphasia called conductive aphasia. People diagnosed with conductive aphasia are capable of understanding what is being said, and are capable of producing speech. However, if you asked a person with conductive aphasia to repeat what you just said he wouldn’t be able to, because that action depends on an intact connection between wernicke’s and broca’s area.
Lateralization
Broca’s and Wernicke’s areas are found in the dominant cerebral hemisphere, which is the left hemisphere in 90% of individuals. Many studies have shown how specialized the dominant hemisphere can be in producing speech. In the 1960’s researcher experimented on patients by injecting sodium amytal, a very rapid-acting anesthetic, into either the right or left carotid artery (the right supplies the right hemisphere the left supplies the left) what was found was that those who had the anesthetic injected in their right carotid thus disabling the right hemisphere were able to respond to question being asked to them, those who had their left hemisphere put to sleep could not. However, the good thing about lateralization of speech is that when damage for example occurs in broca’s or wernicke’s area in the left hemisphere the right homologous area (the same part in the other hemisphere) will take over the functions of the damaged area.
Sources:
http://webspace.ship.edu/cgboer/speechbrain.html
http://news.bbc.co.uk/2/hi/uk_news/magazine/8352525.stm
