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CHAPTER 12
LANGUAGE AND THE BRAIN
The study of the relationship between language and the brain is called neurolinguistics. The field of study dates back to the nineteenth century.
Since that time, a number of discoveries have been made about the specific parts in the brain that are related to language functions. We know that the most important parts are in areas around the left ear. The shaded areas in this illustration indicate the general locations of those language functions involved in speaking and listening. We have come to know that these areas exist largely through the examination, in autopsies of the brains of people who, in life, were known to have specific language disabilities. We have tried to determine where language abilities for normal users must be by finding areas with specific damage in the brains of people who had identifiable language disabilities.
BROCA’S AREA
Paul Broca reported in 1860 that damage to this specific part of the brain was related to extreme difficulty in producing spoken language. It was noted that damage to the corresponding area on the right hemisphere had no such effect. This finding was first used to argue that language ability must be located in the left hemisphere and since then has been treated as an indication that Broca’s area is crucially involved in the generation of spoken language.
WERNICKE’S AREA
Carl Wernicke reported in 1870 that damage to this part of the brain was found among patients who had speech comprehension difficulties. This finding confirmed the left hemisphere location of language ability and led to the view that Wernicke’s area is part of the brain crucially involved in the understanding of speech.
THE MOTOR CORTEX AND THE ARCUATE FASCICULUS
The motor cortex is an area that generally controls movement of the muscles. Close to Broca’s area is the part of the motor cortex that controls the articulatory muscles of the face, jaw, tongue and larynx. Evidence that this area is involved in the physical articulation of speech comes from work reporter in the 1950s by two neurosurgeons. These researchers found that, by applying small amounts of electrical current to specific areas of the brain, they could identify those areas where the electrical stimulation would interfere with normal speech production.
The arcuate fasciculus is known to form a crucial connection between Wernicke’s and Broca’s areas.
THE LOCALIZATION VIEW
Having identified these four components, it is tempting to conclude that specific aspects of language ability can be accorded specific locations in the brain. This is called the localization view and it has been used to suggest that the brain activity involved in hearing a word, understanding it, then saying it, would follow a definite pattern. The word is heard and comprehended via Wernicke’s area. This signal is then transferred via the arcuate fasciculus to Broca’s area where preparations are made to generate a spoken version of the word. A signal is then sent to part of the motor cortex to physically articulate the word.
This is certainly an oversimplified version of what may actually take place, but it is consistent with much of what we understand about simple language processing in the brain. It is probably best to think of any proposal concerning processing pathways in the brain as some form of metaphor that may turn out to be inadequate once we learn more about how the brain functions. The ‘’pathway’’ metaphor seems quite appealing in an electronic age when we are familiar with the process of sending signals through electrical circuits. Sigmund Freud employed a ‘’steam engine’’ metaphor to account for aspects of the brain’s activity when he wrote of the effects of repression ‘’building up pressure’’ to the point of ‘’sudden release’’.
We are forced to use metaphors mainly because we cannot obtain direct physical evidence of linguistic processes in the brain. Because we have no direct access, we generally have to rely on what we can discover through indirect methods. Most of these
stages in the articulation of linguistic expressions. Although the slips are mostly treated as errors of articulation, it has been suggested that they may actually result from slips of the brain as it tries to organize and generate linguistic messages.
SLIPS OF THE EAR
One other type of slip may provide some clues to how the brain tries to make sense of the auditory signal it receives. These have been called slips of the ear and can result, for example, in our hearing great ape and wondering why someone should be looking for one in his office, the speaker actually said ‘’gray tape’’.
A similar type of misunderstanding seems to be behind the child’s report that in Sunday school, everyone was singing about a bear called ‘’Gladly’’ who was cross-eyed. The source of this slip turned out to be a line from a religious song that went Glady the cross I’d bear.
Some problems with language production and comprehension are the result of much more serious disorders in brain function.
APHASIA
BROCA’S APHASIA
The serious language disorder known as Broca’s aphasia is characterized by a substantially reduced amount of speech, distorted articulation and slow, often effortful speech. What is said often consists almost entirely of lexical morphemes. The frequent omission of functional morphemes and inflectional morphemes has led to the characterization of this type of aphasic speech as lacking grammatical forms, or ‘’agrammatic’’. In agramatic speech, the grammatical markers are missing.
An example of speech produced by someone whose aphasia was not severe is the following answer to a question regarding what the speaker had for breakfast:
I eggs and eat and drink coffee breakfast
This type of disorder can be quite severe and result in speech with lots of hesitations and really long pauses.
Some patients can also have lots of difficulty in articulating single words. In Broca’s aphasia, comprehension is typically much better than production.
WERNICKE’S APHASIA
The type of language disorder that results in difficulties in auditory comprehension is sometimes called ‘’sensory aphasia’’ but is more commonly known as Wernicke’s aphasia. Someone suffering from this disorder can actually produce very fluent speech which is often difficult to make sense of. Very general terms are used, even in response to specific requests for information, as in this sample:
I can’t talk all of the things I do, and part of the part I can go alright, but I can´t tell from the other people.
Difficulty in findings the correct word, sometimes referred to as anomia, also happens in Wernicke’s aphasia. Speakers use different strategies such as trying to describe objects or talking about their purpose, as in the thing to put cigarettes in (for ashtray). The speaker tries a range of strategies when he can’t come up with the word.
CONDUCTION APHASIA
This type of aphasia has been associated with damage to the arcuate fasciculus, it is much less common, and it is called conduction aphasia. Individuals suffering from this disorder sometimes mispronounce words, but typically do not have articulation problems. They are fluent, but may have disrupted rhythm because of the pauses and hesitations. Comprehension of spoken words is normally good. The task of repeating a word or phrase creates major difficulty, with forms such as vaysse and fosh being reported as attempted repetitions of the words forms such as ‘’base’’ and ‘’wash’’. What the speaker hears and understands can’t be transferred very successfully to the speech production area.
It should be emphasized that many of these symptoms can occur in all types of aphasia. They can also occur in more general disorders resulting from brain disease, as in dementia and Alzheimer’s disease. Difficulties in speaking can also be accompanied by difficulties in writing. Language disorders of the type we have described are almost always the result of injury to the left hemisphere. This left hemisphere dominance for language has also been demonstrated by another approach to the investigation of language and the brain.
which language acquisition takes place. During childhood, there is a period when the human brain is most ready to receive input and learn a particular language, this is sometimes called the ‘’sensitive period’’ for language acquisition, but is more generally known as the critical period.
From birth until puberty, if a child does not acquire language, for any one of a number of reasons, then he or she will find it almost impossible to learn language later on.
