Dyslexia and the cerebellar deficit hypothesis: A structural MRI approach

Though the cerebellum has traditionally been regarded as a motor area, recent research has linked the cerebellum with cognition (Fiez, Raichle, Balota, & Tallal, 1996; Schmahmann, 1997) including tasks pertaining to language, speech, and reading (Ackermann & Hetrich, 2000; Fabbro, Moretti, & Brava, 2000; Fulbright et al., 1999; Paulesu, Rith, & Fackowiask, 1993). Though there is some debate over the role of the cerebellum in cognition, the cerebellum has continued to be implicated in a number of pathologies, such as ADHD, autism, schizophrenia, and dyslexia (Berquin, et al., 1998; Courchesne, 1997; Rae et al., 1998; Fawcett, Nicolson, & Dean 1996; Fawcett & Nicolson, 1999; Mostofsky, Cooper, Kates, Denckla & Kaufmann, 2004). Given research demonstrating cerebellum involvement with language functioning and speech, its implication in dyslexia has become particularly intriguing. This has led two researchers to develop the cerebellar deficit hypothesis (Nicolson & Fawcett, 1999). The purpose of this study was to examine the cerebellar deficit theory by investigating cerebellum morphology in dyslexia. In addition, an exploratory analysis was performed to look at the probability of familial transference of cerebellar morphology in those with and without dyslexia. A total of 35 families took part in this research project, with groups consisting of participants with dyslexia (18 children, 15 parents) and a control group (22 children, 33 parents). A 1.5 Telsa GE Sigma scanner was used to obtain 3-dimensional structural MRI scans, with statistical analysis of the scans performed with the software package, Analyze 6.0. Results indicated that children with dyslexia showed greater white matter symmetry, particularly within the inferior cerebellar hemispheres, than children without dyslexia. Results of the familial exploratory analysis found that concordant pairs were significantly correlated on posterior-inferior vermis volume, as well as significantly different from the discordant group on right superior cerebellar hemisphere white matter volume. Thus, it could be considered that this study is supportive of the work by Nicolson and Fawcett (2001) which suggests that cerebellar morphological differences can be found in children with dyslexia. Limitations and recommendations for future research studies are presented.