Download Auditory Language & Central Pathways

Central Auditory Pathways,
Functions, and Language
What can we hear?
Subcortical auditory pathways
8th 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
lateral lemniscus
superior olive
cochlear nuclei
Superior olive, human
superior olive
“rabbit-ear” neuron
in cat MSO
axon
Stotler 1953
axons from right
cochlear nuclei
axons from left
cochlear nuclei
“rabbit-ear” neuron
in cat MSO
axon
Stotler 1953
delay spikes by 250 microsec
Do animals with big heads localize sound more accurately?
Head size weakly correlated with sound localization precision
r = -0.425
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)
tonotopic map in AI
low best
frequencies
high best
frequencies
The auditory system is only partially crossed
MGN (medial
geniculate nucleus)
inferior colliculus
superior olive
cochlear nuclei
Primary auditory cortex
AI
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
Beyond A1…Language areas
Left hemisphere, cutaway view
temporal lobe
AI (primary auditory cortex = transverse
temporal gyrus)
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
angular gyrus
Broca’s
area
Wernicke’s area
Functional imaging studies show a different picture
Activating Wernicke’s area in fMRI experiments
angular gyrus
Broca’s
area
Wernicke’s area
fMRI responses to pure tone task
Binder…Prieto, 1997
fMRI responses to language task
angular gyrus
angular gyrus
Broca’s area
Wernicke’s area
regions activated specifically
by listening to words
Binder et al. 1997
angular gyrus
angular gyrus
Broca’s area
Wernicke’s area
regions activated specifically
by listening to words
Binder et al. 1997
primary motor cortex
angular gyrus
premotor
cortex
Broca’s area
Binder et al. 1997
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
Extracting meaning from 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
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?
Normal subjects, activation by reading “horse”, responding “gallop”
Subject #1
Subject #2
Petitto et al. 2000
Normal subjects, activation by reading “horse”, responding “gallop”
Subject #1
Subject #2
Petitto et al. 2000
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