Aphasia is a disruption of language functions caused by brain damage. There are many different forms of aphasia, with specific symptoms largely dependent on the particular location of the brain damage. The study of aphasia has led to the discovery of the specific functions of many brain areas involved in language comprehension and production. The best-known pattern of aphasia is known as Broca’s aphasia, named for the French physician Paul Broca, who first identified the brain area primarily responsible for language production. Located in the left frontal lobe just in front of the primary motor cortex, this area has since been known as Broca’s area.
In 1861 the young surgeon had a fifty-one-year-old patient transferred to his ward with a gangrenous leg. When he attempted to question the patient, Broca discovered that his only response to any question was the nonsense syllable tan. Although he could communicate adequately with gestures, the only sound that would emerge was tan. Broca investigated Tan’s (the patient’s nickname in the hospital) background, discovering that he had first been admitted to the asylum twenty-one years earlier, having lost the ability to speak. The loss occurred gradually, until it finally reached the point where only tan came out when he tried to speak. He clearly understood language, and remained intellectually normal otherwise for his entire hospitalization, though he did eventually develop a paralysis of his right limbs. It should be noted, however, that if he became sufficiently agitated and frustrated by people who failed to understand his gestures, clearer speech would briefly emerge, but only in the form of angry curses.
Tan passed away a mere six days after coming into Broca’s care. Broca, as the chief of surgery, performed the autopsy, during which he discovered that an area about the size of a large chicken egg had been destroyed in Tan’s left frontal lobe. The tissue at the center of the damaged area was completely destroyed, and it was very soft around the edges, suggesting that damage continued to spread. Broca hypothesized that the original lesion had begun at the center of the damaged area and slowly spread, eventually affecting areas in control of the right side of the body. Tan’s pattern of symptoms has since been called Broca’s aphasia, or production aphasia, in which patients show good language comprehension but have disrupted production. Tan was not the first well-documented case of production aphasia, however. The seventeenth century Irish author, Jonathan Swift, also developed the problem late in life, following a very similar pattern, including the ability to curse fluently when angry enough. Tan’s was, however, the first case in which the brain was examined.
Within thirteen years of Broca’s discovery, a German physician discovered the brain area responsible for a different form of aphasia. Carl Wernicke had patients who spoke fluently but made little sense, and they had great difficulty understanding language directed at them. Whereas Broca’s patients had production aphasia, Wernicke’s patients had receptive aphasia, soon to be known as Wernicke’s aphasia. Wernicke discovered that his patients had damage to a small area of the left temporal lobe, a few inches behind Broca’s area. Whereas Broca’s area primarily governs production of language, and smaller lesions there produce difficulties with syntax, Wernicke’s area is responsible for semantics, or comprehension of the meanings of words. Since many head injuries affect more than one area, many aphasic patients have elements of both varieties.
Testing for aphasia often involves a variety of informal language tasks. Spontaneous language production is tested through simple interviewing; if the patient doesn’t spontaneously say anything, this suggests problems with Broca’s area. Simple questions are usually a part of an aphasia interview as well. If the patient fails to answer but appears frustrated by his/her inability to do so, Broca’s aphasia is indicated. If the patient answers, but the responses are incorrect or nonsensical, Wernicke’s aphasia is indicated. One last common element of aphasia assessment involves giving very simple spoken directions, e.g. “Stand up and clap your hands.” The person whose damage is confined to Broca’s area will understand the directions and will comply, whereas damage to Wernicke’s area may cause a failure to understand the directions, resulting in either inaction or the performance of an action other than the one requested.
Bibliography:
- Gregory, R. J. Psychological Testing: History, Principles, and Applications. 4th ed. Boston: Allyn & Bacon, 2004.
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