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