Development of white matter and reading skills

Abstract

White matter tissue properties are highly correlated with reading proficiency; we would like to have a model that relates the dynamics of an individual's white matter development to their acquisition of skilled reading. The development of cerebral white matter involves multiple biological processes, and the balance between these processes differs between individuals. Cross-sectional measures of white matter mask the interplay between these processes and their connection to an individual's cognitive development. Hence, we performed a longitudinal study to measure white-matter development (diffusion-weighted imaging) and reading development (behavioral testing) in individual children (age 7-15 y). The pattern of white-matter development differed significantly among children. In the left arcuate and left inferior longitudinal fasciculus, children with above-average reading skills initially had low fractional anisotropy (FA) that increased over the 3-y period, whereas children with belowaverage reading skills had higher initial FA that declined over time. We describe a dual-process model of white matter development comprising biological processes with opposing effects on FA, such as axonal myelination and pruning, to explain the pattern of results.R eading requires efficient communication within a network of visual, auditory, and language-processing regions that are separated by many centimeters. Hence, the white-matter fascicles that connect these regions are critical for proficient reading (1). Only in the last decade has it become possible to study the microstructural properties of the white matter in the living human brain, and only in recent years has there been an opportunity to trace the developmental progression of these fascicles systematically. During this decade it has been shown that learning to read is associated with corresponding changes in sensory and language circuits in the brain (2-5).Diffusion measurements of the white-matter pathways (3, 5-7) and neurological case studies (8, 9) suggest that in typical development and education both the left hemisphere arcuate fasciculus and inferior longitudinal fasciculus (ILF) carry signals important for reading. Studies in adults, adolescents, and schoolage children have reported differences between good and poor readers in white-matter volume and diffusion properties in the vicinity of these pathways (10-14). One possibility is that these differences are present from an early age, remain constant through development, and constrain children's aptitude for reading. An alternative possibility is that there is an interaction between the biological development and timing of instruction. Two case studies support this hypothesis. When damage to the arcuate fasciculus occurs at birth, normal reading skills can develop (15); when damage to the arcuate fasciculus occurs later, for example after reading instruction has begun, it can result in severe reading impairment (9). These cases suggest that learning depends on the circuits' current state and capacity for plasti...

The Association between Gray Matter Volume and Reading Proficiency: A Longitudinal Study of Beginning Readers

“…The observed differences in volume development between good and poor readers might be due to interindividual differences in the coordination of pruning and growth processes (cf. Yeatman, Dougherty, Ben-Shachar, & Wandell, 2012). Although in better readers, pruning might be more prominent and result in the faster formation of more mature and efficient neural reading circuits, growth processes might dominate development in the poor readers resulting in more diffuse cortical representations.…”

Predicting Developmental Dyslexia: A Brief Review of Genetics, Language and the Brain

“…FA of the entire left arcuate fasciculus also correlates with phonological awareness in school-age children [36], and the volume of the left arcuate fasciculus correlates with phonological awareness in kindergarteners [45]. Furthermore, in a sample of 58 children between ages 5-9, white matter volume changes within the left arcuate fasciculus predict reading outcomes during the developmental period when children become fluent readers [46]. Similarly, the volume of the left arcuate fasciculus and superior corona radiata assessed in 38 children between five-and six-years predicted third grade reading abilities [47].…”

The Relationship between White Matter and Reading Acquisition, Refinement and Maintenance

“…However, the relationship between the developmental trajectory of white-matter tracts and reading acquisition/refinement/ maintenance is yet to be established, and that is the focus of the current study. Here we are defining reading acquisition as the age range of 3-6 years, whereas refinement would include ages from 6 to 14 years and maintenance from ages 14 to 21 years.Longitudinal and cross-sectional studies that assess white-matter maturation and reading development have shed some light on the dynamic relationship between these variables [10][11][12]. Yeatman et al [12] reported that the development of the left arcuate fasciculus (AF; dorsal) and inferior longitudinal fasciculus (ILF; ventral) were related to positive reading gains in children from ages 7 to 15 years and Myers et al [10] extended such findings to include children from kindergarten to grade 3.…”

“…For example, Takeuchi et al [11] performed longitudinal and cross-sectional studies in children and adolescents and reported a positive relationship between reading and FA in the left dorsal (i.e., AF) and ventral (i.e., inferior fronto-occipital fasciculus [IFO] and ILF) tracts. While these studies have showcased the structural basis of white-matter development for reading, there is still much uncertainty about the dynamic nature of this brain-behavior relationship past the initial reading acquisition stage, despite the evidence of white-matter development through adolescence [12]. In addition, it is important to consider white-matter integrity at distinct developmental stages of reading (i.e., acquisition, refinement, maintenance) as each of these stages requires different skills.…”

“…Notably, white matter is highly plastic during development including the school years where there is age-related maturation [8] and changes in response to genetic and experiential factors [9]. One of the experiential factors that are shown to impact white-matter maturation is the process of reading acquisition [10][11][12]. The goal of the current paper is to examine the developmental progression of white-matter pathways as they are related to reading stages associated with reading acquisition (i.e., 3-6 year olds), reading refinement (6-14 years), and reading maintenance (14-21 year olds).…”