No evidence for cerebellar abnormality in adults with developmental dyslexia

Casper A M M Van Oers,Martijn P Van Den Heuvel,L Jaap Kappelle,Gaetano Fiorin,Nadya Goldberg,Frank N K Wijnen

doi:10.1007/s00221-018-5351-y

Casper A M M Van Oers, Martijn P Van Den Heuvel + Show 4 more

Open Access

https://doi.org/10.1007/s00221-018-5351-y

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Abstract

Developmental dyslexia is commonly believed to result from a deficiency in the recognition and processing of speech sounds. According to the cerebellar deficit hypothesis, this phonological deficit is caused by deficient cerebellar function. In the current study, 26 adults with developmental dyslexia and 25 non-dyslexic participants underwent testing of reading-related skills, cerebellar functions, and MRI scanning of the brain. Anatomical assessment of the cerebellum was conducted with voxel-based morphometry. Behavioural evidence, that was indicative of impaired cerebellar function, was found to co-occur with reading impairments in the dyslexic subjects, but a causal relation between the two was not observed. No differences in local grey matter volume, nor in structure–function relationships within the cerebellum were found between the two groups. Possibly, the observed behavioural pattern is due to aberrant white matter connectivity. In conclusion, no support for the cerebellar deficit hypothesis or the presence of anatomical differences of the cerebellum in adults with developmental dyslexia was found.

Highlights

Developmental dyslexia (DD) is a learning disorder that is characterized by difficulties in accurate and fluent written word recognition
The questions we addressed were the following: (a) Do young adults with DD show impaired performance on neuropsychological tasks that typically rely on cerebellar function? (b) Are decrements in cerebellar function associated with reduced reading performance? (c) Do adults with DD show deviations in cerebellar structure? (d) Are there any structural deviations in the cerebellum that are associated with reading impairments or (e) with performance on tasks that rely on cerebellar function?
In this study, using neuropsychological tests and voxel-based morphometry (VBM) to investigate the role of the cerebellum in DD, dyslexics showed impaired performance on a motor task (BT) and cognitive task (TD) that have previously been associated with cerebellar function

Summary

Introduction

Developmental dyslexia (DD) is a learning disorder that is characterized by difficulties in accurate and fluent written word recognition. Nicolson and Fawcett (2007) incorporated the CDH into Ullman’s (2004) procedural/declarative framework for language functions, and proposed a taxonomy of learning disabilities, based on a division of the procedural learning system into corticostriatal and cortico-cerebellar subsystems. These investigators argued that the primary neural deficit in dyslexia is caused by functional disturbances in the language-corticocerebellar system, they stated that it is “premature to rule out language-cortico-striatal involvement in dyslexia” (Nicolson and Fawcett 2007). A critical assumption is that the characteristic symptoms of dyslexia are correlated with the presence of (possibly mild) motor difficulties, and that in the presence of such correlations functional or anatomical abnormalities of the cerebellum should be demonstrable

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