White matter properties and reading in children born preterm: a step forward.

Abstract

This commentary is on the original article by Dodson et al. on pages 695–702 of this issue. Preterm birth seems to be increasing, with an estimated prevalence of 11% of all live births worldwide in 2010.1 Importantly, 31% of children born preterm present lifelong neurodevelopmental effects. Executive function and language/learning difficulties are common sequelae of preterm birth, and are associated with increased health care costs and educational needs. Reading skills are essential for educational progress, as they are the gateway to academic achievement and general knowledge. Together with previous work, the diffusion magnetic resonance study by Dodson et al.2 advances our understanding of the neural basis of this key learning difficulty in children born preterm. Firstly, their findings suggest that phonological awareness is similar in children born at term and preterm at the early stages of learning to read, and that in both groups this ability is supported by dorsal tracts. In view of their results, it would be interesting to explore the association between phonological awareness and white matter microstructure in tracts other than the left-hemisphere arcuate fasciculus in participants born preterm. Positive results might indicate the contribution of compensatory mechanisms that bring the performance of children born preterm up to the level of participants born at term. To address these questions, the use of a whole brain approach that does not require a priori selection of tracts of interest might provide new insights. Secondly, the authors report an association (which is moderated by prematurity) between fractional anisotropy of the right uncinate fasciculus and receptive and expressive language. Interestingly, the authors posit that the lack of association in their preterm sample might be because the uncinate fasciculus myelates late and is slow to develop. Given that participants were in the early stages of learning to read, it would be interesting to monitor their reading acquisition and its neural correlate to check this hypothesis. Additionally, to further understand the origin of reading difficulties in children born preterm and their neural basis, the results should be interpreted in light of studies reporting delayed event-related potentials and mismatch negativity responses to speech sounds in 3-month old children born preterm. It has been suggested that these measures can be used for the early identification of the risk of language impairment.3 One strength of this study is that both fractional anisotropy and mean diffusivity results are reported. These measures are related but different, and so reporting both gives a fuller picture of the neural bases underlying pre-reading skills. Another important strength is that results are controlled for non-verbal intellectual abilities. It might be argued, however, that the basic neuropsychological processes that have been reported to be impaired in children born preterm, such as visual perception and attention,4 may underlie reading difficulties as well. In particular, accurate signalling of shifts of attention by the visual system seem to be a key ability underlying reading performance.5 Thus, the fact that these functions were not directly assessed may represent a limitation. Overall, the study provides novel insights into the similarities and differences of the neurobiology of pre-reading skills in children born preterm and at term. These insights help to explain the previously reported variations observed by this research group in the neurobiology of reading in older participants born at term and preterm. Future studies including children born moderate/late preterm are also warranted as this seems to be the most frequent type of prematurity.1 Finally, we strongly encourage: further research with larger samples; an exploration into the effects of being a pre-reader/reader; the use of a whole brain approach; and ideally a longitudinal follow-up. The information provided by these studies could be used to assist reading acquisition in children born preterm.