Broca's area
| Brain: Broca's area | ||
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| Approximate location of Broca's area highlighted in gray | ||
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| Broca's area visible but not labeled. | ||
| NeuroNames | ancil-251 | |
| Dorlands/Elsevier | a_59/12150965 | |
Broca's area is the section of the human brain (in the opercular and triangular sections of the inferior frontal gyrus of the frontal lobe of the cortex) that is involved in language processing, speech production and comprehension. Broca's and Wernicke's areas are found unilaterally in the brain.
It comprises Brodmann's Area 44,[1] and some authorities also include Brodmann's Area 45[2][3][4]); Broca's Area is connected to Wernicke's area by a neural pathway called the arcuate fasciculus. The corresponding area in macaque monkeys is responsible for high-level control over orofacial actions.[5]
Etymology
Broca's area is named after Pierre Paul Broca, who first described it in 1861, after conducting a post mortem study on a speech-impaired patient.
Parts
There are two main parts of Broca's area, which express different roles during language comprehension and production:
- Pars triangularis (anterior), which is thought to support the interpretation of various 'modes' of stimuli (plurimodal association) and the programming of verbal conducts
- Pars opercularis (posterior), which is thought to support the management of only one kind of stimulus (unimodal association) and the coordination of the speech organs for the actual production of language, given its favorable position close to motor-related areas.
Broca's area and Universal Grammar
Broca's area has been proved to react selectively to languages that follow the set of universal syntactic principles discovered by generative grammarians (cf. generative grammar) especially within the transformational grammar model pioneered by Noam Chomsky and that characterize all and only human languages. For example, if one construes an artificial language where syntactic rules are based on the linear order of words rather than the hierarchical structure of phrases, Broca's area does not play an active role when managing this rule. In fact, in all human languages only hierachy matters rather than linear order in each and every syntactic rule. A simple example is given by the rule of question formation in English sentences involving the copula such as "John is a friend of the girl who is sitting in front of me". The corresponding interrogative question is "is John a friend of the girl who is sitting in front of me?" vs. *"is John is a friend of the girls who sitting in front of me?" but the rule cannot be captured by assuming that it is the first occurrence of the verb that is fronted. In fact, in a simple sentence like "John who is a good cook is a friend of mine" the rule would be falsified, for the correct sentence would be the one where the second occurrence of the verb is fronted: *"is John who a good cook is a friend of mine?" vs. "is John who is a friend of mine a good cook?". To know which verb is to be moved we must rely on the notion of phrase structure - distinguishing for example between the matrix clause vs the embedded one (a relative clause) - rather than the linear order of words on the sequence. Summarizing, it is only with phrase structure rules that Broca's area gets activated not with linear ones. [6] [7]
Aphasia
People suffering from damage to this area may show a condition called Broca's aphasia (sometimes known as expressive aphasia, motor aphasia, or nonfluent aphasia), which makes them unable to create grammatically-complex sentences: their speech is often described as telegraphic and contains little but content words. Patients usually are aware that they cannot speak properly. Comprehension in Broca's aphasia is relatively normal, although many studies have demonstrated that Broca's aphasics have trouble understanding certain kinds of syntactically complex sentences.[8]
This type of aphasia can be contrasted with Wernicke's aphasia, named for Karl Wernicke, which is characterized by damage to more posterior regions of the left hemisphere (in the superior temporal lobe). Wernicke's aphasia manifests as a more pronounced impairment in comprehension. Thus, while speech production remains normal grammatically, it is nonetheless often roundabout, vague or meaningless. It is therefore also known as receptive aphasia.
For example, in the following passage, a Broca's aphasic patient is trying to explain how he came to the hospital for dental surgery.
"Yes... ah... Monday... er... Dad and Peter H... (his own name), and Dad.... er... hospital... and ah... Wednesday... Wednesday, nine o'clock... and oh... Thursday... ten o'clock, ah doctors... two... an' doctors... and er... teeth... yah."[9]
PET and functional MRI have found decreases in activity in the Broca's area in stuttering.There is greater activation of the right hemisphere homologue of the Broca's area (area of Ross) which is believed to be a compensatory response to the hypoactivity in the Broca's area proper. Volumetric MRI has shown that the pars triangularis is smaller in people who stutter.