A PET STUDY IN LANGUAGE

Presentation for Psych 526

Positron Emission Tomography (PET)

PET detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer).

• The concentration of tracer regional glucose uptake tissue metabolic activity or neurochemical activity Fluorodeoxyglucose (FDG) Neurotransmitter receptor ligand (opiate, GABA,

dopamine and serotonin receptor)

Positron Emission Tomography (PET) Animation!

(http://www.sumanasinc.com/webcontent/animations/content/positronemissiontomography.html)

Positron Emission tomography (PET)

• Indirect• can measure metabolism or hemodynamics• can also map brain biochemistry in vivo

• Mildly invasive• injection of radioactive substance

• Spatial resolution• good (5 mm- 1 cm)

• Temporal resolution• poor (seconds-minutes)

• Limitations in experimental paradigms• Very expensive

NEURAL RESPONSES TO THE PRODUCTION AND COMPREHENSION OF SYNTAX IN IDENTICAL UTTERANCES

Peter Indefrey, Frauke Hellwig, Hans Herzog, Rudiger J Seitz, and Peter Hagoort

Psych 526

Big Question

Is there a shared syntactic system between language production and language comprehension?

Anatomy Quiz!

A. Left Rolandic operculumB. Left inferior frontal gyrusC. BA 44D. Broca’s area: Pars triangularis

PET (Indefrey et al, 2001)

Hemodynamic activation for syntactic processing

Kaan & Swaab, 2002

Triangle: Jabberwocky versus a pseudo-word listCircle: Jabberwocky versus restSquare: Syntactic prose versus rest

Black symbols: syntactic violations versus correct sentencesPink symbols: semantic or pragmatic violation versus correct sentences

Black square: passive readingBlack diamond: structure judgment of auditory input

Methods 18 right-handed adults (20-36 yr old) Tasks:

Twelve PET scans per subject. (ABCABCABCABC) (ABC is the random order of SNW)

Production Comprehension (matching/mismatching response)

Anatomical localization procedure The overlap of BA 44 of at least 5 of 10 postmortem

brains. Three-dimensional reconstructions of the 10 brains

based on MR scans Determine the number of brains that agreed in the

assignment of BA 44 for every voxel

Stimuli• Three conditions (SNW)• Full sentence; NP+V; Sequence of word

• Two actions: launch/go to• Three objects: masculine/feminine/neuter• Three colors: red, blue and green

Behavioral Results

Production

ComprehensionAll subjects gave 99.99% correct responses

Sentences

Noun phrases

Single words

Voice onset times 1527 msec

1554 msec *

1550 msec *

Response duration

3288 msec *

3465 msec *

3404 msec

Regional Cerebral Blood Flow (rCBF)

Production of sentences vs. single words One part of caudal BA 44 extending to Rolandic

operculum.

Yellow: Left BA 44 of reference brain (same as Indefrey et al., 2001)

Regional Cerebral Blood Flow (rCBF)

Production S and NP > W No diff b/w S and

NP

No effect of presentation rate

No diff among three conditions in comprehension task.

Other results

Stronger activation of motor-related areas in production conditions

Stronger bilateral temporal activations in the comprehension conditions

Conclusion

BA44 and the adjacent Rolandic operculum is involved in some aspect of syntactic encoding.

The activation patterns of Broca’s area may greatly differ b/w production and comprehension with identical syntactic structures.

Discussion No sensitive region to syntactic complexity in

comprehension Possible candidates: left inferior frontal gyrus, left

or bilateral temporal activation areas. (Friederci et al, 2000; Wong et al, 1999; Kuperberg et al, 2000)

Relative syntactically simple sentences? Particular role of Broca’s area only for syntactically

complex sentences with long antecedent-gap distances (Cooke et al., 2002).

Inteference of semantic processing (lexical semantic strategy)? Stronger focus on semantic processing in agrammatic

aphasia (Haggoort et al, 2003) Stronger activation in “syntactic” system in the

presence of poor semantic cues (Friederici et al, 2000)

More challenges to production task!

Bonnie: How much syntactic planning is there really for

putting an adjective and a noun together (in NP condition)?

Cindy: Paraphrasing the events ("Ok, so the red square

launched the blue ellipse, that means I need to say: Square, Red, Ellipse, Blue, Launch")

Erin: Rehearsal strategy?

That’s why you didn’t see the diff…

Aileen The conditions used for the task were in the order of

ABCABCABC.....participants would probably catch on.

Also how many variations can one generate when the objects performed only 2 specific actions on one another: go next to or go set another object in motion...not many.

Scott: So, although they set out to look at similarities and

differences between production & comprehension, this task obviously wasn't effective at that.

Suggestions to the authors

o Bonnie: Why wouldn’t they use sentences for which syntactic processing actually makes a difference in the meaning? Of course, if you can guess the meaning without the need for syntax you might not use it.

o Aileen: Choose a singing task as control. One would expect the Rolandic operculum to light up despite individual variations in anatomy.

o Xuefei: It is kind of weird to make a conclusion (assumption?) that syntactic production and comprehension are located within the same brain regions (Broca’s area?).

Any other thoughts?