The Functional Neuroanatomy of Language (Part II)
Ling 411 – 22
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.
Patricia Kuhl on learning perceptual distinctions:An example
Fig. 6. (A) Physical distance between /ra-la/ syllables in a grid created byvarying formants 2 and 3 in equal steps. (B) Perceptual distance betweensyllables for American listeners.
A
B
http://www.pnas.org/content/97/22/11850.full.pdf+html
The Functional Neuroanatomy of Language (Part II)
Ling 411 – 22
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 perceptionEvidence 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 perceptionIntra-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 perceptionImaging
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 sensory-motor 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
shoe
He parks the car
It goes between two others
Patient’s Response blackboard
shoelace
He park … he came with the car. He came with his car.
It went two cars … between the cars
Picture naming in conduction aphasia
Picture of..
whistle
pretzel
Patient’s Response
tris.. chi.. trissle.. sissle.. twiss.. ciss.
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 LHphonological 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 InterfaceAlternative 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)
SpeechProduction Speech
Recognition
SMG (proposed by some) Hickok’s alternative: Spt
Auditory-Motor Interface
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
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)
Arguments for the intermediate system hypothesis
Motor and Somatosensory Areas for speech
Mouth
HandFingers
Arm
Trunk
Leg
Central Sulcus
1 2 3
4
1-Phonological production
2-Articulation
3-Articulatory monitoring
4-Phonological monitoring
Post-Central Sulcus
Presumed interconnections of speech areas
Central Sulcus
1 2 34
1 – Phonological production
2 – Articulation
3 – Articulatory monitoring
4 – Phonological monitoring
5 – Primary auditory
6 – Phonological recognition
Post-Central Sulcus
65
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
The Sylvian FissureREVIEW
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)
REVIEW
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 strucureacross 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