A PET STUDY IN LANGUAGE

1. A PET STUDY IN LANGUAGE Presentation for Psych 526

2. 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)

3. Positron Emission Tomography (PET) • Animation! (http://www.sumanasinc.com/webcontent/animations/content/positronemissiontomography.html)

4. 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

5. Psych 526 NEURAL RESPONSES TO THE PRODUCTION AND COMPREHENSION OF SYNTAX IN IDENTICAL UTTERANCES Peter Indefrey, Frauke Hellwig, Hans Herzog, Rudiger J Seitz, and Peter Hagoort

6. Big Question Is there a shared syntactic system between language production and language comprehension?

7. Anatomy Quiz! A. Left Rolandic operculumB. Left inferior frontal gyrusC. BA 44D. Broca’s area: Pars triangularis PET (Indefrey et al, 2001)

8. Hemodynamic activation for syntactic processing Black square: passive reading Black diamond: structure judgment of auditory input Black symbols: syntactic violations versus correct sentences Pink symbols: semantic or pragmatic violation versus correct sentences Triangle: Jabberwocky versus a pseudo-word list Circle: Jabberwocky versus rest Square: Syntactic prose versus rest Kaan & Swaab, 2002

9. 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

10. 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

11. Behavioral Results • Production • Comprehension All subjects gave 99.99% correct responses

12. 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)

13. 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.

14. Other results • Stronger activation of motor-related areas in production conditions • Stronger bilateral temporal activations in the comprehension conditions

15. 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.

16. 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)

17. 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?

18. 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.

19. Suggestions to the authors • 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. • Aileen: Choose a singing task as control. One would expect the Rolandic operculum to light up despite individual variations in anatomy. • 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?).

20. Any other thoughts?