Broca's area

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Brain: Broca's area
BrocasAreaSmall.png
Approximate location of Broca's area highlighted in gray
Broca's area visible but not labeled.
Part of Frontal lobe
Artery Middle cerebral
Vein Superior sagittal sinus
NeuroNames ancil-251
Dorlands/Elsevier a_59/12150965

Broca's area is a section of the human brain that is involved in language processing, speech production, and comprehension. Broca's area is named after the 19th century physician Paul Broca.

Description

Broca's area is located in the opercular and triangular sections of the inferior frontal gyrus of the frontal lobe of the cortex. Broca's and Wernicke's areas are found unilaterally in the brain.

Broca's area comprises Brodmann area 44 [1] and (according to some authorities) Brodmann 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]

Parts

Broca's area has two main parts, 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

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 are usually 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. [6]

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." [7]

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) 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 magnetic resonance imaging (VMRI) has shown that the pars triangularis is smaller in people who stutter.

See also

References

  1. Mohr JP in Studies in Neurolinguistics (eds. Witaker H & Witaker NA) 201–235 (Academic, New York, 1976)
  2. Penfield W & Roberts L Speech and Brain Mechanisms (Princeton Univ Press, Princeton, 1959)
  3. Ojemann GA, Ojemann JG, Lettich E, Berger MS (1989). "Cortical language localization in left, dominant hemisphere. An electical stimulation mapping investigation in 117 patients". J Neurosurg. 71: 316–26. 
  4. Duffau H; et al. (2003). "The role of dominant premotor cortex in language: a study uding intraoperative functional mapping in awake patients". Neuroimage. 20: 1903–14. 
  5. Petrides M, Cadoret G, Mackey S (2005). "Orofacial somatomotor responses in the macaque monkey homologue of Broca's area". Nature. 435: 1235–38. doi:10.1038/nature03628. 
  6. Caramazza A & Zurif E (1976). "Dissociation of algorithmic and heuristic processes in language comprehension: evidence from aphasia". Brain and Language. 3: 572–82. 
  7. Goodglass H & Geschwind N. Language disorders. In E. Carterette and M.P. Friedman (eds.) Handbook of Perception: Language and Speech. Vol II (New York, Academic Press, 1976)
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