Researchers map the neural mechanisms of dyslexia in the brain.

Dyslexia is one of the most widespread learning disabilities. Different therapeutic approaches, and learning strategies are used to tackle the reading and writing difficulties associated with dyslexia, however to-date there is no cure. The main theory is that the cause of dyslexia is a dysfunctional processing of auditory speech, with the reasons for these alterations in speech processing still unknown. Now, a study from researchers at TU Dresden shows people with dyslexia have a weakly developed structure at a subcortical processing stage. The team state their data shows weak white matter connectivity between the left auditory motion-sensitive planum temporale (mPT) and the left auditory thalamus (medial geniculate body, MGB). The study is published in the Journal of Neuroscience.

Previous studies show dyslexia is characterized by the inability to acquire typical reading and writing skills. Although previous neuroimaging research mainly focused on neural mechanisms of dyslexia at the cerebral cortex level, several lines of evidence suggest the malfunctioning of subcortical sensory structures. The current study shows dyslexic male adults have reduced white matter connectivity in a cortico-thalamic auditory pathway between the mPT and MGB.

The current study analyses people with developmental dyslexia in comparison to people without dyslexia, and conducted diagnostic tests and MRI of the brain. Results show people with dyslexia have less fibre connectivity between mPT and MGB in the left hemisphere of the brain than people from the control group. Data findings show the control group exhibit very strong fibre connectivity between mPT and MGB, particularly those who perform well in the reading test.

The lab hypothesized that the amount of left mPT–MGB connectivity correlates with dyslexics rapid naming of letters and numbers (RANln) scores. Diffusion tensor imaging shows that dyslexics have reduced structural connectivity between the left MGB and the left mPT, confirming this hypothesis. Results show stronger left mPT–MGB connectivity was not associated with faster RANln scores in dyslexics, only in neurotypical readers. The group state findings provide the first evidence of reduced cortico-thalamic connectivity in the auditory modality as a feature of developmental dyslexia which may also affect reading abilities in neurotypical readers.

The team surmise they have identified the neural mechanisms of developmental dyslexia. For the future, the researchers state understanding the neural mechanisms of developmental dyslexia will be decisive for the development of early diagnostics and of targeted therapies.

Source: Technische Universität Dresden

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