title: White matter lateralization and interhemispheric coherence to auditory modulations in normal reading and dyslexic adults.
abstract: Neural activation of slow acoustic variations that are important for syllable identification is more lateralized to the right hemisphere than activation of fast acoustic changes that are important for phoneme identification. It has been suggested that this complementary function at different hemispheres is rooted in a different degree of white matter myelination in the left versus right hemisphere. The present study will investigate this structure-function relationship with Diffusion Tensor Imaging (DTI) and Auditory Steady-State Responses (ASSR), respectively. With DTI we examined white matter lateralization in the cortical auditory and language regions (i.e. posterior region of the superior temporal gyrus and the arcuate fasciculus) and white matter integrity in the splenium of the corpus callosum. With ASSR we examined interhemispheric coherence to slow, syllabic-rate (i.e. 4 Hz) and fast, phonemic-rate (i.e. 20 Hz) modulations. These structural and functional techniques were applied in a group of normal reading adults and a group of dyslexic adults for whom previously reduced functional interhemispheric connectivity at 20 Hz has been reported (Poelmans et al. (2012). Ear and Hearing, 33, 134-143). This sample was chosen since it is hypothesized that in dyslexic readers insufficient hemispheric asymmetry in myelination might relate to their auditory and phonological problems. Results demonstrate reduced white matter lateralization in the posterior superior temporal gyrus and the arcuate fasciculus in the dyslexic readers. Additionally, white matter lateralization in the posterior superior temporal gyrus and white matter integrity in the splenium of the corpus callosum related to interhemispheric coherence to phonemic-rate modulations (i.e. 20 Hz). Interestingly, this correlation pattern was opposite in normal versus dyslexic readers. These results might imply that less pronounced left white matter dominance in dyslexic adults might relate to their problems to process phonemic-rate acoustic information and to integrate them into the phonological system.
authors.affiliation: ExpORL, Department of Neurosciences, KU Leuven, Herestraat 49, 3000 Leuven, Belgium; Parenting and Special Education Research Unit, KU Leuven, Leopold Vanderkelenstraat 32, PO Box 3765, 3000 Leuven, Belgium; Radiology Section, KU Leuven, Herestraat 49, 3000 Leuven, Belgium. Electronic address: Maaike.Vandermosten@ppw.kuleuven.be.
authors.forename: Maaike
authors.initials: M
authors.lastname: Vandermosten
authors.forename: Hanne
authors.initials: H
authors.lastname: Poelmans
authors.forename: Stefan
authors.initials: S
authors.lastname: Sunaert
authors.forename: Pol
authors.initials: P
authors.lastname: Ghesquière
authors.forename: Jan
authors.initials: J
authors.lastname: Wouters
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001921:Brain / Q000503:physiopathology*; D003337:Corpus Callosum / Q000503:physiopathology*; D056324:Diffusion Tensor Imaging; D004410:Dyslexia / Q000503:physiopathology*; D004569:Electroencephalography; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007802:Language; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D011932:Reading
keywords: AM; ASSR; CCsplenium; DTI; Dyslexia; FA; Interhemispheric coherence; STGp; White matter; amplitude modulation; auditory steady-state responses; diffusion tensor imaging; fractional anisotropy; posterior region of the superior temporal gyrus; splenium of the corpus callosum