Language-general and -specific white matter microstructural bases for reading

Abstract

In the past decade, several studies have investigated language-general and -specific brain regions for reading. However, very limited research has examined the white matter that connects these cortical regions. By using diffusion tensor imaging (DTI), the current study investigated the common and divergent relationship between white matter integrity indexed by fractional anisotropy (FA) and native language reading abilities in 89 Chinese and 93 English speakers. Conjunction analysis revealed that for both groups, reading ability was associated with the FA of seven white matter fiber bundles in two main anatomical locations in the left hemisphere: the dorsal corona radiate/corpus callosum/superior longitudinal fasciculus which might be for phonological access, and the ventral uncinate fasciculus/external capsule/inferior fronto-occipital fasciculus which might be for semantic processing. Contrast analysis showed that the FA of the left temporal part of superior longitudinal fasciculus contributed more to reading in English than in Chinese, which is consistent with the notion that this tract is involved in grapheme-to-phoneme conversion for alphabetic language reading. These results are the first evidence of language-general and –specific white matter microstructural bases for reading.

Individual differences in decoding skill, print exposure, and cortical structure in young adults

“…We have mentioned one such study, in which vocabulary knowledge informed our understanding of the structural significance of pSMG (Lee et al, 2007). There are others exploring relations between the connectivity of regions in the left-hemisphere reading network and, for example, decoding ability (Welcome & Joanisse, 2014; Zhang et al, 2014; in dyslexic readers, see Pugh et al, 2000; Steinbrink et al, 2008). Taking white matter structure into account could be particularly important since increased white matter myelination decreases the space between the cortex and the skull, potentially contributing to grey matter thinning (Lu et al, 2007; Sowell et al, 2004).…”

Harmonizing DTI measurements across scanners to examine the development of white matter microstructure in 803 adolescents of the NCANDA study

“…No model detected a maximum for the uncinate fasciculus, which is reported to develop with reading and language skills (Paldino et al, 2014). These late-developing fiber systems included the superior longitudinal fasciculus, which has been identified in meta-analyses as the tract most consistently reported to be associated with continued development (Peters et al, 2012) and integral to selective functions of verbal fluency, reading (Hoeft et al, 2011; Zhang et al, 2014), vocabulary (Tamnes et al, 2010b), and working memory (Ostby et al, 2011; Vestergaard et al, 2011). Other late-developing tracts were the superior frontal occipital fasciculus (for background, Schmahmann and Pandya, 2007), damage to which has been found in spatial neglect (Shinoura et al, 2009; Shinoura et al, 2010), and the sagittal stratum, which intersects with language areas (Menjot de Champfleur et al, 2013) and, along with other association fasciculi, can sustain microstructural damage with functional ramifications following traumatic brain injury (Farbota et al, 2014).…”

White matter plasticity and reading instruction: Widespread anatomical changes track the learning process

“…We began by replicating previously reported correlations between reading skill and properties of the white matter tracts connecting key components of the reading circuitry [1][2][3][4][5][6][7][8][9]14,15,18,[35][36][37][38][39][40] . To summarize individual differences in reading, we report Reading Skill, a composite score that incorporates our full battery of reading tests from the Woodcock-Johnson 51 and TOWRE 52 standardized assessments (see Methods for details, and Supplementary Figure 1A).…”

“…Skilled reading requires orchestration of a large cortical network, and individual differences in reading performance have been linked to the properties of white matter tracts connecting portions of this network specialized for processing visual, acoustic, and semantic features [1][2][3][4][5][6][7][8][9] . Although individual differences in white matter are thought to reflect the joint influence of genetics and experience [10][11][12] , white matter properties are often held to underlie variation in performance and to causally influence individual learning trajectories [13][14][15][16] .…”

“…Using a longitudinal intervention design, we track improvements in reading skills, and accompanying changes in white matter, in a group of grade-school aged, struggling readers during 8 weeks of intensive (4 hours each day, 5 days a week), one-on-one training in reading skills. We first examine learning effects within three tracts thought to carry signals critical for skilled reading [1][2][3][4][5][6][7][8][9]14,15,18,[35][36][37][38][39][40] : the left arcuate fasciculus (AF), left inferior longitudinal fasciculus (ILF), and posterior callosal connections (CC). These pathways connect canonical reading-related regions within the ventral occipitotemporal (including the visual word form area, or VWFA [41][42][43][44][45][46][47] ), superior temporal 48,49 , and inferior frontal cortex 50 , and hence, these tracts are considered to be part of the core circuitry for reading 37,46,47 .…”