Reading, dyslexia and the brain

Background: Neuroimaging offers unique opportunities for understanding the acquisition of reading by children and for unravelling the mystery of developmental dyslexia. Here, I provide a selective overview of recent neuroimaging studies, drawing out implications for education and the teaching of reading. Purpose: The different neuroimaging technologies available offer complementary techniques for revealing the biological basis of reading and dyslexia. Functional magnetic resonance imaging (fMRI) is most suited to localisation of function, and hence to investigating the neural networks that underpin efficient (or inefficient) reading. Electroencephalography (EEG) is sensitive to millisecond differences in timing, hence it is suited to studying the time course of processing; for example, it can reveal when networks relevant to phonology versus semantics are activated. Magnetic source imaging (MSI) gives information about both location in the brain and the time course of activation. I illustrate how each technology is most suited to answering particular questions about the core neural systems for reading, and how these systems interact, and what might go wrong in the dyslexic brain. Design and methods: Following a brief overview of behavioural studies of reading acquisition in different languages, selected neuroimaging studies of typical development are discussed and analysed. Those studies including the widest age ranges of children have been selected. Neuroimaging studies of developmental dyslexia are then reviewed, focusing on (a) the neural networks recruited for reading, (b) the time course of neural activation and (c) the neural effects of remediation. Representative studies using the different methodologies are selected. It is shown that studies converge in showing that the dyslexic brain is characterised by under-activation of the key neural networks for reading. Conclusions: Different neuroimaging methods can contribute different kinds of data relevant to key questions in education. The most informative studies with respect to causation will be longitudinal prospective studies, which are currently rare.