| الوصف: |
Background DCDC2 is a leading susceptibility gene in Developmental Dyslexia (DD) and reading ability. A DCDC2/intron 2 deletion (DCDC2d), encompassing the Regulatory Element Associated with Dyslexia 1 (READ1) region, has been linked to DD and structural and functional brain areas underlying reading acquisition in subjects with DD and in normal readers (NR) (for a review, Mascheretti et al., 2017). DCDC2d influences motion perception, a psychophysical characteristic tapping the magnocellular (M) stream, in reading (dis)ability (Cicchini et al., 2015; Gori et al., 2015). The M stream provides early accurate visual analysis of stimuli prior to grapheme-phoneme integration (Vidyasagar, 1999). Data reveal its impairment in DD (Stein, 2014). To investigate DCDC2d effects on M stream functionality, we implemented an fMRI study on children with DD and NR, grouped according to the presence(+)/absence(-) of DCDC2d, to assess contrast sensitivity at different temporal and spatial frequencies tapping the M and parvocellular (P) streams. Methods We studied 53 children: 11 DD+ (mean age:14.1±1.9; F/M:1/10), 16 DD- (mean age:13.9±1.7; F/M:5/11), 8 NR+ (mean age:12.9±1.6; F/M:4/4), 18 NR- (mean age:12.1±1.9; F/M:7/11), with a block-design fMRI visual task on a 3 T scanner (TR=2 s, voxel 3×3×3.5mm3; time 12’04”). The stimuli consisted of two full-field sinusoidal gratings shown for 14 s at different orientations with sinusoidal counterphase flicker to activate either the M or P streams (Denison et al., 2014). Subjects performed a target detection task during 16 M and 8 P pseudorandom blocks, to encourage them to constantly follow the visual stimuli. A 2-way ANOVA in SPM12 (Friston et al., 2007) tested the main effects and interactions of DD and DCDC2d. The significance threshold was p The local Bioethics Committee approved the study and parents gave written informed consent. Results During the M stimuli, subjects with DCDC2d, regardless of DD, showed reduced activation in the left V1, and higher activations in the right precuneus, the left fusiform and temporal gyri, and insula. Moreover, children with DD, regardless of DCDC2d, showed reduced activations in the left V1, lingual gyrus and right fusiform gyrus, and higher activation in the left middle and superior temporal gyrus. No significant interactions were found at the significance threshold. Discussion During a visual task stimulating the M streams, irrespective of DD, DCDC2d accounted for activations in primary visual cortex and reading-related brain areas in the ventral stream involved in word recognition, phonological processing and grapheme-phoneme correspondence (fusiform and temporal gyri), and in speech and language processing (insula). Findings suggest that new hypothesis-driven imaging–genetic studies would lead to the identification of neurofunctional variations belonging to the DD ‘functional phenotype’. As previously described, children with DD showed different activations in visual (V1) and reading-related brain areas (lingual, fusiform and temporal gyri), supporting the idea that altered cortico-cortical connectivity of the language and visual areas might represent a mechanism underlying DD. Finally, significant interactions between DD and DCDC2d may plausibly exist; larger sample sizes are needed to support this hypothesis and to confirm this preliminary data. |
