Transcript Ling 411 – 22 The Functional Neuroanatomy of Language (Part II) Applying the findings about columnar organization Christine Cooper: I have recently been thinking.

Ling 411 – 22
The Functional Neuroanatomy
of Language (Part II)
Applying the findings about columnar organization
Christine Cooper:
I have recently been thinking a lot about the broader
implications, and even potentially applications, of all of the
knowledge on columnar organization. It seems to me like this
information could be invaluable to childcare and education.
http://www.pnas.org/content/97/22/11850.full.pdf+html
Patricia Kuhl on
learning
perceptual
distinctions:
An example
Fig. 6. (A) Physical
distance between
/ra-la/ syllables in a
grid created by
varying formants 2
and 3 in equal steps.
(B) Perceptual
distance between
syllables for
American listeners.
A
B
Ling 411 – 22
The Functional Neuroanatomy
of Language (Part II)
Some earlier findings w.r.t. RH speech perception
 Vowel qualities
 Intonation
 Tones in tone languages
Imaging studies
 When listening to spoken discourse, cerebral blood flow
increases in
• Wernicke’s area
• Broca’s area
• RH homologues of Wernicke’s and Broca’s areas
 More cerebral blood flow in RH when subjects read
sentences containing metaphors than literal sentences
Experiments (described by Beeman)
 Words presented to rvf-LH or lvf-RH
 RH more active than LH
• Synonyms
• Co-members of a category: table, bed
• Polysemy: FOOT1 – FOOT2
• Metaphorically related connotations
• Sustains multiple interpretations
 LH about same as RH
• Other associations: baby-cradle
 LH more active than RH
• Choose verb associated with noun
Patients with brain-damage
 Some patients with LH damage
• Can’t name fruits but can say that they are fruits
 Patients with RH damage
• Impaired comprehension of metaphorical statements
• More difficulty producing words from a particular
semantic category than producing words beginning
with a particular letter (258)
Experiments on speech perception
 Dichotic listening – normal subjects
• Right ear (i.e. LH) advantage for distinctions of
 Voicing
 Place of articulation
• Left hear (RH) advantage for
 Emotional tone of short sentences
• Sentences presented in which only intonation
could be heard
 RH advantage for identifying sentence type
– declarative, question , or command
Experiments on speech perception
 Split brain patients
• They hear a consonant
• Then written representations are presented
• ‘Point to the one you heard’
• rvf-LH exhibited strong advantage
Patients with right-brain damage
 Posterior RH lesions result in deficits in
interpreting emotional tone
 Anterior RH lesions abolish the ability to
control the production of speech intonation
Split-brain studies
 Isolated RH has ability to read single words
• But not as fast nor as accurate as LH
• Ability declines with increasing word length
• Lexical context does not assist letter identification
 In Japanese subjects
• RH is better at reading kanji than kana
• LH is better at reading kana
RH involvement in speech perception
Evidence from an earlier paper by Hickok
 Evidence from tests of isolated RH
• Split-brain studies
• Wada test
 Sodium amytol, sodium barbitol
• Discrimination of speech sounds
• Comprehension of syntactically simple speech
(Hickok 2000: 92)
Caution – Split-Brain Studies
 These patients are generally epileptics
 Usually the onset of seizures is several to many years
before the surgery
 Often the onset of seizures was during childhood
 Therefore the brain has had time to adapt – perhaps
reorganize some linguistic functions
RH involvement in speech perception
Intra-operative recording
 Evidence from intraoperative recording
 Sites found in STG of both hemispheres for
• Phoneme clusters
• Distinguishing speech from backwards speech
• Distinguishing mono- from polysyllabic words
(Hickok 2000: 92-3)
RH involvement in speech perception
Imaging
 Evidence from imaging
• PET
• fMRI
• MEG
 Subjects passively listen to speech
 Both hemispheres show activity
• More activity in LH
 Some evidence for differential contributions of the two
hemispheres (Hickok & Poeppel, another publication)
(Hickok 2000: 93)
5. Phonological processing systems in speech
recognition are bilateral but asymmetric
 Hickok: “The hypothesis that phoneme-level processes in
speech recognition are bilaterally organized does not
imply that the two hemispheres are computationally
identical.
 “In fact there is strong evidence for hemispheric
differences in the processing of acoustic/speech
information [2,17,68,90,193].”
 Basis of the differences? – Two views
• Temporal (LH) vs. spectral (RH) resolution
• Difference in sampling rate
 LH: 25-50 Hz
 RH: 4-8 Hz
Another opportunity for either-or thinking:
Explaining differential functions of LH and RH (127)
 One possibility:
• Temporal vs. spectral resolution
 Another possibility (Zatorre):
• Different sampling rates
 LH – 25-50 Hz
 RH – 4-8 Hz
 It’s not either-or!
Fig. 5. Serial vs. parallel models of speech recognition
“The processing levels may be distributed across the two hemispheres in some
fashion and may correspond to different temporal windows of integration”
Possible bases for RH/LH difference
 Higher ratio of white to gray matter in RH
• Therefore, higher degree of connectivity in RH
 Difference in dendritic branching
 Different density of interneurons
 Evoked potentials (EEG) are more diffuse over the
RH than over LH
Beeman 257
Grammatical and semantic/conceptual information
 There’s a lot we don’t know
 Hickok: “The neural organization of conceptual-semantic
systems is a matter of debate” (127)
 What we do know:
• Lexico-grammatical and semantic-conceptual – 2 levels
• Semantic-conceptual is very widely distributed
 Different areas for different categories (cardinal noses)
• Areas commonly implicated:
 Posterior MTG and ITG
• Also, other temporal areas
 AG
Hickok’s Fig. 1
Hickok: MTG/ITG (LH and RH) are “important in mapping sound onto meaning”
ATL (LH) implicated by some in “lexical-semantic and sentence-level processing”
7. Posterior language cortex in the left hemisphere is
involved in phonological aspects of speech production
 Hickok gets it right: Wernicke’s area is heavily involved in
speech production
• Provides additional evidence (q.v. – 128, 129)
• “Given these behavioral observations, it is no surprise that
posterior sensory-related cortex in the left hemisphere have been
found to play an important role in speech production.” (129)
Wernicke’s area in speech production
“What I would like to suggest is that
Wernicke was essentially correct in
hypothesizing … that auditory cortex
participates in speech production …”
(Hickok 2000: 89)
Hickok quotes Wernicke:
Observations of daily speech usage and the process of
speech development indicates the presence of an
unconscious, repeated activation and simultaneous
mental reverberation of the acoustic image which
exercises a continuous monitoring of the motor images.
Wernicke 1874
Evidence for left pSTP* involvement in speech
production
 Erratic speech of Wernicke’s aphasics
 Conduction aphasia from damage to left pSTP*
 Intraoperative stimulation of left pSTP*
• “distortion and repetition of words and syllables” (Penfield & Roberts
1959)
• N.B.: As in Wernicke’s aphasia
 MSI study shows activity in left pSTG just before speech
production (picture naming) (Levelt et al. 1998)
 fMRI study: similar results – no RH activity shown (Hickok et
al. 1999)
(Hickok 2000: 93-4)
*pSTP: posterior Supra-Temporal Plane
Spt: active in both perception and production (Fig. 8A)
“A number of fMRI studies have demonstrated the
existence of an area in the left posterior Sylvian region
(area Spt, Fig. 8A) that responds both during the
perception and production of speech (Fig. 8B), even
when speech is produced covertly (subvocally)…” (130)
“Conduction aphasics…typically have damage involving
Spt” (132)
Area “Spt” (proposed by Hickok & Poeppel)
“We occasionally get questions regarding how to define area Spt
-- the key dorsal-stream region we believe performs sensorymotor transformations for speech. The acronym stands for
Sylvian parietal temporal to reflect the fact that it is located
within the Sylvian fissure at the parietal-temporal boundary. The
region involves a portion of the planum temporal/parietal
operculum (very hard to distinguish the two), and is a
subportion of area tpt.”
http://www.talkingbrains.org/2007/05/where-is-area-spt.html
Seems to overlap with the TPO junction area and/or SMG
Area “Spt” in an fMRI experiment
http://www.talkingbrains.org/search/label/commentary
Area Spt not just for speech
Also involved in
music perception
and production
(humming)
Subdivisions of Planum temporale (Fig. 6)
“Note that there are four different
fields within the planum temporale
suggesting functional differentiation,
and that these fields extend beyond
the planum temporale”
Problem with Hickok’s proposal
 Hickok proposes that
• phonological recognition is bilateral
• but conduction aphasia results from Spt in LH
 Problem: When patients are given words to repeat
• Conduction aphasics keep trying
• Wernicke aphasics don’t
• Indicates that Wernicke aphasics don’t perceive their
own speech
 Another problem: Wernicke aphasia usually results from
LH damage only
Repetition in Wernicke’s aphasia
Model for Repetition
 black
Patient’s Response
 blackboard
 shoe
 shoelace
 He parks the car
 He park … he came with the
car. He came with his car.
 It goes between two others
 It went two cars … between
the cars
Picture naming in conduction aphasia
 Picture of..
 Patient’s Response
 whistle
 tris.. chi.. trissle..
sissle.. twiss.. ciss.
 pretzel
 trep.. tretzle..
trethle.. tredfl… ki
Lamb’s email query to Hickok (April 1, 2010)
Hi Greg - In my neurolinguistics class we have just been
considering your 2000 paper from the Grodzinsky et al. volume,
with its new perspective on, among other things, these two types
of aphasia. Very intriguing, but I have a question:
How do you explain this:
When you give a conduction aphasic words to repeat, he/she
commonly produces a phonemic paraphasia and then keeps
trying, since he/she recognizes the error; but a Wernicke's aphasic
usually stops after one incorrect repetition, evidently unaware of
the error.
Acc. to your proposal, both types of aphasic have LH
phonological recognition wiped out, and both have intact RH pSTG.
Hickok’s response (April 1, 2010)
Hi Syd, Good to hear from you. That is an interesting question. I
think there are two possibilities. One is that the conduction
aphasics don't have as much damage to the left hemisphere
phonological systems we (I) might have thought. I.e., the damage
is more often involving the posterior Sylvian region (Spt). The
intact left and right hemi phonological systems allow the patient
to clearly recognize their errors and self correct. Wernicke's on
the other hand typically have extensive damage to the left hemi
phonological systems which, because of their role in production,
may have a larger role in self monitoring. Another possibility,
perhaps in conjunction with the first, is that Wernicke's have
damage to semantic (access) systems as well. it may be much
harder to notice a phonological error if you can't tell whether it is
a word or not.
The Perception-Production Interface
Alternative views
 We have phonological recognition in Wernicke’s area
• And in RH homolog of Wernicke’s area
 And phonological production in Broca’s area
• And in RH homolog of Broca’s area
 Clearly, they have to be connected
 The traditional view
• Direct connection: the arcuate fasciculus
• Proposed by Wernicke, supported by Geschwind
 Alternative view
• Supramarginal gyrus (SMG) as intermediary
• Proposed by Hickok
 with support from Damasio and Goldstein
The Intermediate System Hypothesis
(Two versions)
Auditory-Motor
Interface
Speech
Production
Speech
Recognition
SMG (proposed by some)
Hickok’s alternative: Spt
Arguments for the Direct
Connection Hypothesis
 No additional intervening structure needed
 We have anatomical evidence for the arcuate fasciculus
• And for its connections from Wernicke’s area to
Broca’s area
Arguments for the intermediate system hypothesis
 Damasio cites SMG damage as a major cause of conduction
aphasia
• Consistent with earlier findings of Goldstein
 “Central aphasia” (Goldstein 1948)
 Connectivity studies in non-human primates fail to find
direct connection between auditory cortex and ventral
posterior frontal lobe
• But support the claim that the lower parietal lobe provides an
interface between these areas (Hickok 2000: 99)
 SMG is a likely site of higher-level proprioceptive
processing of speech
Arguments for the intermediate system hypothesis
 Damasio cites SMG damage as a major cause of
conduction aphasia
• Consistent with earlier findings of Goldstein
 “Central aphasia” (Goldstein 1948)
 Anatomical studies in macaque monkeys fail to find direct
connection (between corresponding areas) (Hickok 2000: 99)
 SMG is a likely site of higher-level proprioceptive
processing of speech
• (next slide)
Motor and Somatosensory Areas for speech
Central
Sulcus
1-Phonological
production
Post-Central
Sulcus
Leg
Trunk
Arm
2-Articulation
3-Articulatory
monitoring
4-Phonological
monitoring
Hand
Fingers
1
2Mouth3
4
Presumed interconnections of speech areas
Central
Sulcus
Post-Central
Sulcus
1 – Phonological
production
2 – Articulation
3 – Articulatory
monitoring
4 – Phonological
monitoring
5 – Primary
auditory
6 – Phonological
recognition
4
1
2 3
5
6
And there’s more than meets the eye
 The phonological recognition area
includes the temporal plane
 The phonological monitoring area
includes the parietal operculum
 Both very large areas
REVIEW
The Sylvian Fissure
REVIEW
Evidence for left pSTP involvement in speech
production
 Erratic speech of Wernicke’s aphasics
 Conduction aphasia from damage to left pSTP
 Intraoperative stimulation of left pSTP
• “distortion and repetition of words and syllables” (Penfield & Roberts
1959)
• N.B.: As in Wernicke’s aphasia
 MSI study shows activity in left pSTG just before speech
production (picture naming) (Levelt et al. 1998)
 fMRI study: similar results – no RH activity shown (Hickok et
al. 1999)
(Hickok 2000: 93-4)
Diffusion Tensor Imaging (DTI)




New and very informative technique
Uses MRI
Allows observation of molecular diffusion in living tissues
Makes use of
• Brownian movement
• Magnetic properties of hydrogen nuclei
 Two of them in every water molecule (H2O)
 Water moves along lines of least resistance
• i.e., along white matter axons
 aided by myelin
Arcuate fasciculus in primates
Asif Ghazanfar, Nature Neuroscience 11:4.382-384, April 2008
Uniformity of cortical strucure
across mammals?
 The hypothesis of uniformity
• Very important for perceptual neuroscience
• Allows data from experiments on cats and monkeys to
be applied to human cortical structure and function
 Including higher levels – language
 But: this hypothesis applies to grey matter
• Not white matter
 Cortico-cortical connections
 DTI shows that white matter connections differ across
mammals
Arcuate fasciculus in different primates
Asif Ghazanfar, Nature Neuroscience 11:4.382-384, April 2008
Friederici Figure 2
Fiber tracts between Broca's and Wernicke's area. Tractography
reconstruction of the arcuate fasciculus using the two-region of interest
approach. Broca's and Wernicke's territories are connected through direct and
indirect pathways. The direct pathway (long segment shown in red) runs
medially and corresponds to classical descriptions of the arcuate fasciculus.
The indirect pathway runs laterally and is composed of an anterior segment
(green), connecting Broca's territory and the inferior parietal cortex
(Geschwind's territory), and a posterior segment (yellow), connecting
Geschwind's and Wernicke's territories.
end