Anatomy of language processing Mark Harju

Most components for language processing are located in the left hemisphere Most components for language processing are located in the left hemisphere Left= dominant language hemisphere Left= dominant language hemisphere Nearly all right-handed people Nearly all right-handed people Two-thirds of lefties Two-thirds of lefties The cortical area most involved in the left hemisphere is central around the sylvan fissure The cortical area most involved in the left hemisphere is central around the sylvan fissure

The two most traditionally distinct areas are The two most traditionally distinct areas are  Wernicke’s area

The two most traditionally distinct areas are The two most traditionally distinct areas are  Wernicke’s area  Broca’s area

Wernicke’s area comprises a region that includes: Wernicke’s area comprises a region that includes:  the posterior part of the superior temporal gyrus  parietooccipitotemporal junction, including the angular gyrus

Wernicke’s area is concerned with the comprehension of spoken language. Wernicke’s area is concerned with the comprehension of spoken language. The angular gyrus has to do with comprehension of written language The angular gyrus has to do with comprehension of written language

Broca’s area comprises a region covering the posterior part of triangular gyrus Broca’s area comprises a region covering the posterior part of triangular gyrus Opercular gyrus in the inferior frontal gyrus Opercular gyrus in the inferior frontal gyrus

Broca’s area is concerned with speech production Broca’s area is concerned with speech production Within Broca a vocalization program is formulated Within Broca a vocalization program is formulated

This program transmits to the face, tongue, vocal chords, and pharynx areas of the motor cortex for execution of speech. This program transmits to the face, tongue, vocal chords, and pharynx areas of the motor cortex for execution of speech.

It is also connected with the supplementary motor area, which is concerned with the initiation of speech. It is also connected with the supplementary motor area, which is concerned with the initiation of speech.

Broca and Wernicke are connected by the arcuate fasciculus Broca and Wernicke are connected by the arcuate fasciculus A fiber bundle pathway, necessary for repetition of spoken language A fiber bundle pathway, necessary for repetition of spoken language

The cortical areas are used in sequence when processing language. The cortical areas are used in sequence when processing language.

For example, if you were reading aloud you would need to involve your visual cortex, located in your occipital lobe For example, if you were reading aloud you would need to involve your visual cortex, located in your occipital lobe

You would also need your primary motor cortex to use your face, tongue, vocal chords, and pharynx to speak You would also need your primary motor cortex to use your face, tongue, vocal chords, and pharynx to speak

….And your supplementary motor cortex in order to initiate speech. ….And your supplementary motor cortex in order to initiate speech.

The output from the visual cortex goes to the angular gyrus, where it links the image of the written words to language. The output from the visual cortex goes to the angular gyrus, where it links the image of the written words to language.

Then to Wernicke’s area where the words are processed and given meaning Then to Wernicke’s area where the words are processed and given meaning

Then through the arcuate fasciculus to Broca’s area, where the vocalization of the words is formulated Then through the arcuate fasciculus to Broca’s area, where the vocalization of the words is formulated

Then the vocalized program is delivered to the primary motor cortex, and initiated into speech by a signal to the supplementary motor cortex. Then the vocalized program is delivered to the primary motor cortex, and initiated into speech by a signal to the supplementary motor cortex.

Another example Another example

In the case of speaking words you hear, you would need to involve In the case of speaking words you hear, you would need to involve

The auditory cortex to hear the words The auditory cortex to hear the words

The primary motor cortex to use your face The primary motor cortex to use your face

And the supplementary motor cortex to tell your face to start talking. And the supplementary motor cortex to tell your face to start talking.

Boom. You are saying what you have heard. Boom. You are saying what you have heard.

A quick word on language in the right hemisphere A quick word on language in the right hemisphere Corresponding areas have been measured as metabolically active in right hemisphere during speech Corresponding areas have been measured as metabolically active in right hemisphere during speech This is believed to be linked with melodic function of speech (prosody) This is believed to be linked with melodic function of speech (prosody)

This may explain some cases of autism or brain damage where the subjects are unable to speak yet are able to sing This may explain some cases of autism or brain damage where the subjects are unable to speak yet are able to sing