Authors: Richards, T. L., Grabowski, T. J., Boord, P., Yagle, K., Askren, M., Mestre, Z., Robinson, P., Welker, O., Gulliford, D., Nagy, W., & Berninger, V.
Publication: Neuroimage: Clinical (Elsevier). 8, 408–421 2015 | DOI: 10.1016/j.nicl.2015.03.018
- • We studied DTI structural white matter integrity and functional fMRI connectivity in children with dysgraphia and dyslexia.
- • There were significant differences between control group and both the dysgraphic and dyslexic groups in DTI parameters.
- • There were significant differences between control group and both the dysgraphic and dyslexic groups in functional connectivity.
- • The dysgraphic and dyslexic groups differed on radial diffusivity (RD) in seven left-sided fiber tracts.
- • The significance of these contrasting complex brain patterns is discussed in reference to the human connectome.
Based on comprehensive testing and educational history, children in grades 4–9 (on average 12 years) were diagnosed with dysgraphia (persisting handwriting impairment) or dyslexia (persisting word spelling/reading impairment) or as typical writers and readers (controls). The dysgraphia group (n = 14) and dyslexia group (n = 17) were each compared to the control group (n = 9) and to each other in separate analyses. Four brain region seed points (left occipital temporal gyrus, supramarginal gyrus, precuneus, and inferior frontal gyrus) were used in these analyses which were shown in a metaanalysis to be related to written word production on four indicators of white matter integrity and fMRI functional connectivity for four tasks (self-guided mind wandering during resting state, writing letter that follows a visually displayed letter in alphabet, writing missing letter to create a correctly spelled real word, and planning for composing after scanning on topic specified by researcher). For those DTI indicators on which the dysgraphic group or dyslexic group differed from the control group (fractional anisotropy, relative anisotropy, axial diffusivity but not radial diffusivity), correlations were computed between the DTI parameter and fMRI functional connectivity for the two writing tasks (alphabet and spelling) by seed points. Analyses, controlled for multiple comparisons, showed that (a) the control group exhibited more white matter integrity than either the dysgraphic or dyslexic group; (b) the dysgraphic and dyslexic groups showed more functional connectivity than the control group but differed in patterns of functional connectivity for task and seed point; and (c) the dysgraphic and dyslexic groups showed different patterns of significant DTI–fMRI connectivity correlations for specific seed points and written language tasks. Thus, dysgraphia and dyslexia differ in white matter integrity, fMRI functional connectivity, and white matter–gray matter correlations. Of clinical relevance, brain differences were observed in dysgraphia and dyslexia on written language tasks yoked to their defining behavioral impairments in handwriting and/or in word spelling and on the cognitive mind wandering rest condition and composition planning.
Richards, T. L., Grabowski, T. J., Boord, P., Yagle, K., Askren, M., Mestre, Z., Robinson, P., Welker, O., Gulliford, D., Nagy, W., & Berninger, V. (2015). Contrasting brain patterns of writing-related DTI parameters, fMRI connectivity, and DTI-fMRI connectivity correlations in children with and without dysgraphia or dyslexia. NeuroImage. Clinical, 8, 408–421.
The dysgraphia group showed greater functional connectivity than the control group only during the planning for composing task for three of the seed points but not for the left supramarginal gyrus seed point. The dysgraphia group did not differ from the control group during resting condition (mind wandering without another-imposed task). In contrast, the dyslexia group had stronger functional connectivity than the control group during resting state (mind wandering) and always in the left-occipital temporal gyrus, consistent with dyslexics’ problems in self-regulation of processes involved in written word spelling, but not during planning. The dysgraphia group did not differ from the control group on the two language production tasks, but the dyslexia group had greater functional connectivity than the control group, especially in the cerebellum, on both the alphabet letter writing and spelling tasks. The dyslexic group was overconnected compared to the dysgraphic group in the left inferior parietal lobe and primary and secondary somatosensory cortex.
It was surprising that, compared to the control group, the dysgraphic and dyslexic groups differed in contrasting ways on two kinds of cognitive tasks related to writing, but not assessed on conventional measures of intellectual function. Specifically, the dysgraphic group showed more functional connections from three seed points (all but left supramarginal gyrus) than the control group or dyslexic group on planning for composing; but the dyslexic group showed more functional connections during flow in the resting condition compared to the controls from one seed point (left occipital temporal gyrus). However, when the dyslexic and dysgraphic groups were compared to each other the pattern of overconnectivity changed from that for comparison with controls. For both mind wandering during rest and planning for composing, the dysgraphics showed more functional connectivity from all four seed points.