Vandermosten, M. M., Hoeft, F., & Norton, E. S. (2016). Integrating MRI brain imaging studies of pre-reading children with current theories of developmental dyslexia: A review and quantitative meta-analysis. Current Opinion in Behavioral Sciences, 10, 155–161. doi:10.1016/j.cobeha.2016.06.007
A meta-analysis of functional and structural neuroimaging studies in young prereaders (Vandermosten, Hoeft, & Norton, 2016) shows evidence of differences that look like those observed in older children and adults. A study like this is important because it can help differentiate between brain areas implicated in poor reading skills due to an underlying functional or structural anomaly versus areas altered due to years of struggling with learning to read.
The development of reading skills in school-aged children is fundamental to achieving academic performance goals. It is sometimes easy to forget that reading is a learned skill—a skill that is not hardwired into our brains, but is acquired by tapping resources our brains have available to accomplish the task. Learning to read is a complex process formally taught to children in their earliest years of school. Though most children successfully navigate the process of learning to read, some struggle with the core components of reading, including automatic word identification, fluency, and text comprehension.
Developmental dyslexia is the most common learning disability identified in young children, yet the etiology (i.e., the underlying cause) of dyslexia remains poorly understood. Because dyslexia is more common in related rather than unrelated individuals, genetic influences substantially affect measures of reading ability. Similarly, properties of brain structure and function are also highly heritable, suggesting that altered features of brain development underlie problems in learning to read for children with dyslexia. However, the role of environmental factors, particularly the availability and extent of reading experience, can also have a significant impact on measures of reading ability. Thus, a key issue is whether atypical brain structure and function described in neuroimaging studies of developmental dyslexia emerge from a lack of quality reading experience or interfere with skill development in reading ability. Although challenging, resolving this issue has implications for maximizing individual response to reading intervention strategies.
Only recently have MRI protocols for evaluating brain structure and function become child-friendly (i.e., quick to acquire and not too loud) and feasible for young prereaders. Given the strong genetic component contributing to developmental dyslexia, prereaders can be identified as being at risk for developing dyslexia if there is a family history of reading difficulties. Imaging the at-risk prereaders and following them until their reading abilities can be characterized as typical or dyslexic would be the ideal study design. However, very few studies have been able to take this approach. Yet several research groups have conducted imaging studies comparing at-risk and not-at-risk prereaders for developing dyslexia. Consistently, across these studies, differences between at-risk and not-at-risk prereaders have resembled findings in older children and adults with and without dyslexia. Thus, altered brain development typically observed in older children and adults with dyslexia is already present in children at risk for developing dyslexia before formally learning to read.
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