Broca's area · Grey Matter

Broca's area is the part of the left inferior frontal gyrus that helps turn an intended message into spoken, grammatical language: it is involved in planning the articulation of words and in building and parsing sentence structure.

Broca's area. Broca's area is the part of the left inferior frontal gyrus that helps turn an intended message into spoken, grammatical language: it is involved in planning the articulation of words and in building and parsing sentence structure.

It covers the pars opercularis and pars triangularis (Brodmann areas 44 and 45), just in front of the part of the motor cortex that moves the lips, tongue and larynx. Paul Broca described it in 1861 from the brain of a patient who could say little more than one syllable, and it became the first function located in a specific patch of cortex. In most people it is on the left, part of the left-lateralised language network described on the lateralisation card, and it connects with Wernicke's area through the arcuate fasciculus and the other fibres of the dorsal stream.

Its role extends beyond speaking. Area 44 is engaged in processing complex syntax in comprehension too, and in sequencing actions outside language.

A lesion confined to this area causes less than its name suggests. Damage limited to Broca's area usually produces a transient disturbance of speech; the lasting Broca's aphasia needs a larger lesion that reaches the insula, the underlying white matter and the surrounding frontal cortex.

The right-hemisphere counterpart contributes to the melody and emphasis of speech (prosody).

Questions: How do Broca's and Wernicke's areas work together when you repeat a word you just heard? The heard word is analysed in the auditory cortex and the superior temporal gyrus, both sides contributing. To repeat it, a left-dominant dorsal stream maps the sound onto the movements that would produce it, through the temporoparietal junction and the arcuate fasciculus to the inferior frontal cortex and premotor areas. A ventral stream along the temporal lobe meanwhile maps the sound onto its meaning, which is what understanding needs. Damage to the dorsal link with both ends spared gives conduction aphasia, in which repetition fails out of proportion to speaking and understanding. If Broca's area makes speech, why does a lesion confined to it rarely cause lasting Broca's aphasia? Speech production is a network, and Broca's area (left Brodmann areas 44 and 45) is one node in it, beside the insula, the motor and premotor cortex for the mouth, and the white matter that links them to the temporal lobe. In 1978 Mohr and colleagues found that a stroke limited to Broca's area produced mutism or effortful speech that recovered within weeks, while the full, lasting syndrome followed large lesions of the territory around it. Even the brains of Broca's own patients, scanned in 2007, showed damage reaching well beyond the area that carries his name. Is language on the left side of the brain in everyone? In most people it is, and the share depends on handedness. Measuring blood flow in both hemispheres during word generation, Knecht and colleagues found right-hemisphere dominance in about 4 % of strong right-handers, 15 % of ambidextrous people and 27 % of strong left-handers, with the rest left-dominant or bilateral. So most left-handers are left-dominant for language too, and a right-hemisphere stroke causes aphasia only in the minority whose language sits on that side.