Central Auditory Pathways, Functions, and Language Central Auditory Pathways, Functions, and Language

What can we hear?

Subcortical auditory pathways

8 th nerve (vestibulocochlear )

brachium of the inferior colliculus lateral lemniscus

Sound Localization

Cue 1: Delay between time of sound arrival at left and right ears (speed of sound in air = 342 m/sec)

Cue 2: Sound is louder in one ear than the other

cochlear nuclei superior olive lateral lemniscus

Superior olive, human superior olive

axon “rabbit-ear” neuron Stotler 1953 in cat MSO

axon “rabbit-ear” neuron axons from right cochlear nuclei axons from left cochlear nuclei Stotler 1953 in cat MSO

delay spikes by 250 microsec

Do animals with big heads localize sound more accurately?

Head size weakly correlated with sound localization precision r = Heffner 1997

Density of retinal ganglion cells, 3 species Heffner 1997

Width of high acuity visual field is strongly correlated with sound localization precision r = 0.92

MGN (medial geniculate nucleus)

Left hemisphere, cutaway view temporal lobe AI (primary auditory cortex = transverse temporal gyrus)

low best frequencies high best frequencies tonotopic map in AI

cochlear nuclei superior olive MGN (medial geniculate nucleus) inferior colliculus The auditory system is only partially crossed

AI Primary auditory cortex

After lesion of AI … Can still identify sounds Can understand speech reasonably well Poor localization of sound in contralateral half of space

After lesion of AI … Can still identify sounds Can understand speech reasonably well Poor localization of sound in contralateral half of space

Beyond A1…Language areas

Left hemisphere, cutaway view temporal lobe AI (primary auditory cortex = transverse temporal gyrus) Beyond A1…Language areas

Broca’s aphasia (expressive aphasia): difficulty in speaking or writing Wernicke’s aphasia (receptive aphasia): difficulty in understanding speech or written material

Broca’s area lesions

Broca’s aphasia (expressive aphasia): difficulty in speaking or writing Wernicke’s aphasia (receptive aphasia): difficulty in understanding speech or written material

Wernicke’s area lesions

Wernicke’s area Broca’s area angular gyrus

Functional imaging studies show a different picture

Wernicke’s area Broca’s area angular gyrus Activating Wernicke’s area in fMRI experiments

fMRI responses to pure tone task Binder…Prieto, 1997

fMRI responses to language task

angular gyrus regions activated specifically by listening to words angular gyrus Broca’s area Wernicke’s area Binder et al. 1997

angular gyrus Broca’s area Wernicke’s area regions activated specifically by listening to words Binder et al. 1997

premotor cortex angular gyrus primary motor cortex Broca’s area Binder et al. 1997

scrambled sentence: And disappeared the bushes rabbit down the into bounded hill the meaningful sentence: The rabbit bounded down the hill and disappeared into the bushes From words to sentences…

scrambled sentence: And disappeared the bushes rabbit down the into bounded hill the meaningful sentence: The rabbit bounded down the hill and disappeared into the bushes From words to sentences…

scrambled sentence: And disappeared the bushes rabbit down the into bounded hill the meaningful sentence: The rabbit bounded down the hill and disappeared into the bushes activity when reading meaningful sentences minus activity when reading scrambled sentences Extracting meaning from sentences

lesions cause problems in naming objects or people (anomic aphasia)

Some areas in left hemisphere used in language processing

Where are language areas in deaf people who communicate with sign language?

Petitto et al Normal subjects, activation by reading “horse”, responding “gallop” Subject #1 Subject #2

Normal subjects, activation by reading “horse”, responding “gallop” Petitto et al Subject #1 Subject #2

Deaf subjects, view signs for “horse”, respond with signs for “gallop” Petitto et al. 2000

In deaf people who communicate with sign language, Broca’s area helps produce signed speech

Deaf subjects: view signs for “horse”, respond with signs for “gallop” Petitto et al. 2000

In deaf people who communicate with sign language, auditory cortex helps out with language processing