Methods Effective functional connectivity of phonological and semantic processing processing during...
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Transcript of Methods Effective functional connectivity of phonological and semantic processing processing during...
Methods
Effective functional connectivity of phonological and semantic processing processing during word reading
Cheryl M. Capek1,2, Simandeep Poonian1 and Joseph T. Devlin1,2
Cognitive, Perceptual & Brain Sciences, UCL, UK1, Institute of Cognitive Neuroscience UCL, UK 2
Results
• Activation in aIFC present for Semantics > Phonology
Introduction
• 32 (14M, 18F) participants• Mean age = 24.6 years (s.d. = 5.1)• Native English speakers• Monolingual• Right handed
• Stimuli: word pairs• Phonology task (“Do the words rhyme?”)
• Independent of orthography• Semantic task (“Do the words belong to the same semantic category?”)• 100 word pairs / condition; matched on: word length, number of letter &
syllables, frequency, familiarity, imageability, concreteness • Mixed design with jittered ISI (4-10s, mean=7)• Two lists; order counterbalanced
• Scanning: 1.5T Siemens Avanto scanner, GE-EPI, TR =3s, TE =50ms, 3x3x3.5 mm resolution
• Analysis (SPM5)• Second-level random effects: task>fixation & phonology vs. semantics• DCM (Friston et al., 2003):
• Volumes of interest defined for each subject:1. ventral occipito-temporal cortex (vOTC)2. supramarginal gyrus (SMG) 3. posterior inferior frontal cortex (pIFC)4. anterior inferior frontal cortex (aIFC) IFC)
• Definition based on:• Activation in effects-of-interest F-map (p < .001, uncorrected) in all
four anatomically constrained regions• 26 subjects met the inclusion criteria
Discussion• Group activations consistent with previous studies
showing word reading elicits activation in a widely distributed brain network including our 4 ROIs
• Our findings show: 1. Very strong evidence favouring the simpler model with
pair-wise functional connectivity between:• vOTC SMG• SMG posterior IFC• Posterior anterior IFC• vOTC anterior IFC
2. Activity was modulated by task• Semantic task increased BOLD signal magnitude in
anterior IFC
• Phonological task increased functional coupling between vOTC and posterior IFC, although it unclear how this is mediated anatomically
1. Discrepancy between location of modulatory effects in the two models suggests it is not
vOTC SMG pIFC• Fully-connected model suggests another
pathway linking vOTC and pIFC, which may correspond to the inferior occipito-frontal fasciculus
1) Results are consistent with two anatomical-functional routes to reading (Plaut et al.,1996; Coltheart et al., 2001)• Dorsal route that is dominant for phonological
processing (Saur et al., 2008; Mechelli et al, 2005)• Ventral route that is dominant for semantic processing
(Catani et al., 2003; Binder et al., 2005)• No clear evidence for an independent third (i.e.
lexical) route
AcknowledgementsThis research was supported by the Wellcome Trust
ReferencesBinder, J. R., Medler, D. A., Desai, R., Conant, L. L., & Liebenthal, E. (2005). Some
neurophysiological constraints on models of word naming. Neuroimage, 27(3), 677-693.Catani, M., Jones, D. K., Donato,.Coltheart, M., Rastle, K., Perry, C., Langdon, R., & Ffytche, D. H. (2003). Occipito-temporal
connections in the human brain. Brain, 126(Pt 9), 2093-2107 R., & Ziegler, J. (2001). DRC: a dual route cascaded model of visual word recognition and reading aloud. Psychol Rev, 108(1), 204-256.
Demonet, J. F., Chollet, F., Ramsay, S., Cardebat, D., Nespoulous, J. L., Wise, R., et al. (1992). The anatomy of phonological and semantic processing in normal subjects. Brain, 115 ( Pt 6), 1753-1768.
Friston, K. J., Harrison, L., & Penny, W. (2003). Dynamic causal modelling. Neuroimage, 19(4), 1273-1302.
Gough, P. M., Nobre, A. C., & Devlin, J. T. (2005). Dissociating linguistic processes in the left inferior frontal cortex with transcranial magnetic stimulation. J Neurosci, 25(35), 8010-8016.
Mechelli, A., Crinion, J. T., Long, S., Friston, K. J., Lambon Ralph, M. A., Patterson, K., et al. (2005). Dissociating reading processes on the basis of neuronal interactions. J Cogn Neurosci, 17(11), 1753-1765.
Plaut, D. C., McClelland, J. L., Seidenberg, M. S., & Patterson, K. (1996). Understanding normal and impaired word reading: computational principles in quasi-regular domains. Psychol Rev, 103(1), 56-115.
Poldrack, R. A., Wagner, A. D., Prull, M. W., Desmond, J. E., Glover, G. H., & Gabrieli, J. D. E. (1999). Functional specialization for semantic and phonological processing in the left inferior prefrontal cortex. NeuroImage, 10, 15-35.
Saur, D., Kreher, B. W., Schnell, S., Kummerer, D., Kellmeyer, P., Vry, M. S., et al. (2008). Ventral and dorsal pathways for language. Proc Natl Acad Sci U S A, 105(46), 18035-18040.
• No significant difference on accuracy or RT across the phonology and semantic tasks
Phonology > fixation Semantics > fixation
Behavioural (n=32)
Random Effects (n=32)
idea+
notion
knows+
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Aims of the current study:
1) to determine functional connectivity between the regions of LIFC and the temporal lobes
2) to investigate whether this is significantly modulated by task
3) to determine whether the functional connections correspond to anatomical fronto-temporal connections
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Anatomically-Constrained Model
Fully-Connected model
DCMs (n = 26)
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• Lesion and neuroimaging studies reliably show that word reading involves regions of the left hemisphere including:• Ventral occipito-temporal cortex (vOTC)• Inferior parietal cortex (e.g., SMG)• Inferior frontal cortex (IFC)
• Neuroimaging (Poldrack, 1999; Demonet, 1992, Fiez et al., 1997) and neurostimulation (Gough & Devlin, 2005) studies show evidence of functionally distinct subdivisions in the LIFC:• Phonology -posterior IFC• Semantics -anterior IFC
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Semantics > PhonologyPhonology > Semantics - n.s. p < .001 (uncorrected)
• For both models: all intrinsic connections significant at p < .01
• Model comparison: Anatomically-constrained model favoured for each subject (Bayes Factors: mean = 24,171 (range: 365 - 258,000))
• Significant modulatory effects for Phonology only
Phonology
Baseline
Semantics
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• All 4 ROIs are significantly active for both tasks (at p<0.001 uncorrected)
pIFC
aIFC
SMG
vOTC
SMG
vOTC
L R L R
L R
Activations (≥ 10 voxels) overlaid on mean T1-weighted image
p < .05 (corrected) p < .05 (corrected)
p < .001 (uncorrected)
• Significant modulatory effect for Phonology (p < .01)
• Modulatory effect for Phonology (p = .11)
• Significant modulatory effect for Phonology (p = .03) Contact: [email protected]
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