Effective functional connectivity of phonological and semantic processing processing during word reading
Cheryl M.
1,2
Capek ,
Simandeep
Cognitive, Perceptual & Brain Sciences, UCL,
1
Poonian
1
UK ,
and Joseph T.
1,2
Devlin
Institute of Cognitive Neuroscience UCL, UK
Introduction
Results
• 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
Accuracy
RT
1600
95
1500
90
1400
msec
100
85
1200
75
1100
70
1000
Phon
Sem
Phonology
Phon
Sem
Phonology
Semantics
Random Effects (n=32)
Semantics
Activations (≥ 10 voxels) overlaid on mean T1-weighted image
Phonology > fixation
Semantics > fixation
R
L
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
SMG
R
L
SMG
pIFC
pIFC
pIFC
aIFC
pIFC
aIFC
vOTC
vOTC
p < .05 (corrected)
p < .05 (corrected)
Phonology > Semantics - n.s.
• 32 (14M, 18F) participants
• Mean age = 24.6 years (s.d. = 5.1)
• Native English speakers
• Monolingual
• Right handed
Semantics > Phonology
p < .001 (uncorrected)
• 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)
DCMs (n = 26)
Anatomically-Constrained Model
Semantics
• Modulatory effect for Phonology (p = .11)
+
freight
wolf
+
drain
+
plate
0.24
0.24
sour
0.67
0.29
+
+
• Significant modulatory effect for Phonology (p < .01)
0.47
lake
your
sea
+
0.30
0.27
Fully-Connected model
33sec
time
• Scanning:
15s
33s
Baseline
…
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
0.24
• For both models: all intrinsic
connections significant at p < .01
• Model comparison: Anatomicallyconstrained model favoured for each
subject (Bayes Factors: mean =
24,171 (range: 365 - 258,000))
• Significant modulatory effects for
Phonology only
• 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
• 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
3. 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
References
0.42
+
• Group activations consistent with previous studies
showing word reading elicits activation in a widely
distributed brain network including our 4 ROIs
2. Activity was modulated by task
• Semantic task increased BOLD signal magnitude in
anterior IFC
• All 4 ROIs are significantly active for both tasks (at p<0.001 uncorrected)
Methods
Phonology
• No significant
difference on
accuracy or RT
across the
phonology and
semantic tasks
1300
80
idea
+
notion
knows
+
nose
Discussion
Behavioural (n=32)
Mean % Correct
• 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)
+
2
0.15
0.15
0.24
0.20
0.15
0.53
0.21 0.34
0.35
0.19
0.23
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.
Acknowledgements
This research was supported by the Wellcome Trust
• Significant modulatory effect for Phonology (p = .03)
Contact: c.capek@ucl.ac.uk