The Brain: speak a word that is read Credit: Dr. Eric Chudler

To speak a word that is read, information must first get to the primary visual cortex. From the primary visual cortex, information is transmitted to the posterior speech area, including Wernicke's area. From Wernicke's area, information travels to Broca's area, then to the Primary Motor Cortex.

To speak a word that is heard, information must first get to the primary auditory cortex. From the primary auditory cortex, information is transmitted to the posterior speech area, including Wernicke's area. From Wernicke's area, information travels to Broca's area, then to the Primary Motor Cortex.

The Brain: speak a word that is heard Credit: Dr. Eric Chudler

Damage to Broca's Area Credit: Dr. Eric Chudler

The language problems associated with damage to Broca's and Wernicke's area are quite different from one another: Damage to Broca's Area (Broca's aphasia) prevents a person from producing speech person can understand language words are not properly formed speech is slow and slurred. Damage to Wernicke's Area (Wernicke's aphasia) loss of the ability to understand language person can speak clearly, but the words that are put together make no sense. This way of speaking has been called "word salad" because it appears that the words are all mixed up like the vegetables in a salad.

In most people (97%), both Broca's area and Wernicke's area are found in only the left hemisphere of the brain. In the early 1950's, the famous neurosurgeon Wilder Penfield and his colleague Herbert Jasper, described how electrical stimulation of certain areas of the brain blocked language. These neurosurgeons were able to perform these studies asking their patients questions during the surgical procedure. More recently (late 1980's), Dr. George Ojemann at the University of Washington has used electrical stimulation experiments to show that there can be a large difference in the brain area that is important for language from person to person. Nevertheless, the results of these studies agree with the earlier findings of Broca and Wernicke.

In 1960, another technique was discovered that allowed researchers to study the brain mechanisms of language. This method, called the Wada Test, uses a fast acting anesthetic called sodium amytal (amobarbital) to put one hemisphere of the brain asleep. The sodium amytal is injected into the right or left carotid artery. The right artery supplies the right cerebral hemisphere and the left artery supplies the left cerebral hemisphere. Therefore, either the right or left hemisphere can be "put to sleep" temporarily. If the left hemisphere is put to sleep in people who have language ability in the left hemisphere, then when asked to speak, they cannot. However, if the right hemisphere is put to sleep, then these people will be able to speak and answer questions.

Studies performed in people who have received electroconvulsive shock treatment have also confirmed that language is found most often on the left side. The most recent technique used to study language is by using brain imaging techniques. Positron emission tomography studies show that many of the expected areas of the brain have increased blood flow during language tasks, but there are also areas on both hemispheres that are activated. Therefore, it appears that even the hemisphere that is not dominant for language (usually the right side) has some involvement in language. Actually, people have problems communicating the emotions involved with language when they have damage to the right side of the brain in the area where on the left side it is used for language. This disorder is called an "aprosodia".