Language and the Brain

[ESAL SPIRIT]

Of course, language is a function of the peculiar structure of the human brain. Several areas of the brain have been identified with linguistic skills, such as producing and understanding speech. Furthermore, people with brain damage in specific areas have difficulties with very specific aspects of language, implying that it is a highly compartmentalized process. Furthermore, human brains are functionally asymmetrical, concentrating many areas essential for speech production in one hemisphere.



The Structure of the Brain

In many animals that use sound for communication, the brain is lateralized, placing the control of sound production in one hemisphere of the brain (usually the left); this takes place quite strongly in songbirds and somewhat in monkeys, dolphins, and mice. The phenomenon of lateralization is extremely strong in humans, and in the vast majority language areas are concentrated in the left hemisphere. The right hemisphere controls language in only about 3% of right-handers and 19% of left-handers, and another 68% of left-handers have language circuitry in both hemispheres.
There are two major areas of the human brain that are responsible for language: Broca's area, which is though to be partially responsible for language production (putting together sentences, using proper syntax, etc.) and Wernicke's area, which is thought to be partially responsible for language processing (untangling others' sentences and analyzing them for syntax, inflection, etc.). Other areas involved in language are those surrounding the Sylvian fissure, a cleavage line separating the portions of the brain that are exclusively human from those we share with other animals. In general, the areas that control language would be adjacent to one another if the human brain was laid out as a flat sheet.



Broca's Aphasia

When people experience damage to Broca's area or its surroundings, their disorder is called Broca's aphasia. As predicted by the central role of Broca's area in language production, Broca's aphasics produce slow, halting speech that is rarely grammatical. Typical Broca's aphasics eliminate inflections such as -ed and words not central to the meaning of the sentence, such as the and and. They generally retain their vocabularies and have no difficulty naming objects or performing other meaning-related tasks. In general, they can deduce the meanings of sentences from general knowledge, but cannot understand sentences whose syntax is essential to their meaning. They are fully aware of their difficulties and the rest of their faculties are unimpaired.
The difficulties experienced by Broca's aphasics reveal that Broca's area is central to correct processing and production of grammatical information. However, some Broca's aphasics retain certain grammatical abilities, including the ability to process certain types of syntax. Moreover, the difficulty that Broca's aphasics experience in actual production of speech is also enigmatic; a problem that affected exclusively grammar would not necessarily create difficulty in speaking - only in speaking grammatically. As a result, Broca's area is clearly involved in grammar and language, but there may be other areas in the brain with overlapping functions, and it may not be the seat of all grammatical processing power.



Wernicke's Aphasia

When people experience damage to Wernicke's area, the result is a disorder called Wernicke's aphasia, which is in some ways the opposite of Broca's aphasia. Wernicke's aphasics are able to produce generally grammatical sentences, but they are often nonsensical and include invented words. Wernicke's aphasics show few signs of understanding others' speech, and have difficulty naming objects; they commonly produce the names of related objects or words that sound similar to the object's name.
The symptoms experienced by Wernicke's aphasics seem to support the idea that Wernicke's are is related to the correct processing of others' communication. It also implies that Wernicke's area could be involved in the retrieval of words from the mental dictionary.



Other Types of Aphasia

Other types of aphasia noted in brain-damaged patients produce even stranger results. If Wernicke's and Broca's area are disconnected, patients cannot repeat sentences they have just heard. This implies that perhaps Wernicke's area, which has processed the sentence heard, is unable to communicate it to Broca's area for repetition. In another type, Wernicke's and Broca's areas remain connected but cannot communicate with the rest of the brain. These patients can only repeat sentences; they cannot speak spontaneously. This suggests that Wernicke's and Broca's areas are doing their jobs, but are not receiving input about what to talk about from the rest of the brain and are therefore paralyzed except when others produce speech.