Methods

1. 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 Introduction Results Discussion DCMs (n = 26) Random Effects (n=32) Behavioural (n=32) • 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 • Group activations consistent with previous studies showing word reading elicits activation in a widely distributed brain network including our 4 ROIs • Our findings show: • Very strong evidence favouring the simpler model with pair-wise functional connectivity between: • vOTC  SMG • SMG  posterior IFC • Posterior  anterior IFC • vOTC  anterior IFC • 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 • 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 • 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 Accuracy RT • No significant difference on accuracy or RT across the phonology and semantic tasks msec Mean % Correct Phonology Semantics Phonology Semantics Activations (≥ 10 voxels) overlaid on mean T1-weighted image idea + notion knows + nose Phonology > fixation Semantics > fixation R L R L SMG Aims of the current study: to determine functional connectivity between the regions of LIFC and the temporal lobes to investigate whether this is significantly modulated by task to determine whether the functional connections correspond to anatomical fronto-temporal connections SMG pIFC pIFC pIFC pIFC aIFC aIFC vOTC vOTC p < .05 (corrected) p < .05 (corrected) • All 4 ROIs are significantly active for both tasks (at p<0.001 uncorrected) Methods Phonology > Semantics - n.s. p < .001 (uncorrected) Semantics > Phonology • 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 R L • Activation in aIFC present for Semantics > Phonology aIFC p < .001 (uncorrected) Anatomically-Constrained Model Semantics Phonology • Modulatory effect for Phonology (p = .11) + + • Significant modulatory effect for Phonology (p < .01) 0.47 wolf drain freight plate + + 0.24 0.24 0.67 0.29 • References • Binder, 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. + + 0.42 sour your 0.30 lake sea + + 0.27 Fully-Connected model 33s 33sec 15s … time Baseline 0.24 0.15 • 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 • 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 0.15 0.24 0.20 0.53 0.15 0.21 0.34 0.35 0.19 0.23 Acknowledgements This research was supported by the Wellcome Trust • Significant modulatory effect for Phonology (p = .03) Contact: c.capek@ucl.ac.uk