Broca's area

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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.

It can also be described as Brodmann's Area 44, and 45 and is connected to Wernicke's area by a neural pathway called the arcuate fasciculus.

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.

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.

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. 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.¹

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, and speech that seems normal grammatically but is often roundabout, vague or meaningless.

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."².

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.

See also

• pars opercularis
• pars triangularis
• plurimodal association
• unimodal association
• arcuate fasciculus
• cortex
• human brain
• language
• Wernicke's area
• expressive aphasia

References

¹Caramazza, A., & Zurif, E. 1976. Dissociation of algorithmic and heuristic processes in language comprehension: evidence from aphasia. Brain and Language, 3, 572-582.

²Goodglass, H. & Geschwind, N. (1976) Language disorders. In E. Carterette and M.P. Friedman (eds.) Handbook of Perception: Language and Speech. Vol II. New York: Academic Press.

 

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