The neural basis of dyslexia may originate in primary auditory cortex

This scientific commentary refers to ‘Neuroanatomical precursors of dyslexia identified from pre-reading through to age 11’ by Clark et al. (doi:10.1093/brain/awu229). Longitudinal research studies that follow at-risk samples before a disorder is evident, ideally from infancy, are the gold standard in the field of neurodevelopmental disorders (Goswami, 2014). They are also the rarest. In this issue of Brain , Clark and colleagues report a longitudinal structural neuroimaging study of children at high versus low risk of dyslexia that began before reading instruction commenced. The structural scans were taken the year before reading was taught (at age 6), a year after reading tuition began (at age 8), and after dyslexia had been diagnosed (at age 11). Clark et al. ’s study thereby reveals the neurodevelopmental trajectory of the dyslexic brain, the only sure means of disentangling cause from effect in the aetiology of a neurodevelopmental disorder.Longitudinal studies are crucial because the acquisition of reading is one of the most complex cognitive feats that the brain achieves. As young children learn to recode print to sound, the brain undergoes intensive and highly specific experience-dependent learning, often on a daily basis. These learning experiences selectively train aspects of sensory processing and attention. For example, oculomotor control and small shifts of visuospatial attention may be practised for hours every day. Learning to read literally changes the brain. Therefore, the identification of pre-reading weaknesses in neural structures and processes is vital to understanding causation in developmental dyslexia.Clark and colleagues followed Norwegian children from preschool until sixth grade, identifying participants at high risk of dyslexia on the basis of family risk. They also followed a matched sample of children at low risk for dyslexia. The children’s neurocognitive skills were assessed yearly. Norwegian is a relatively transparent orthography, and reading instruction commences at …