Dyslexia, Motor Control, and the Cerebellum

Developmental Dyslexia (DD) is defined as a learning disorder that is
neurological in origin and is characterized by difficulties in accurate and
fluent written word recognition and by poor spelling and reading abilities,
despite normal intelligence, normal hearing, adequate classroom exposure, and
absence of physical, emotional and socioeconomic problems [International
Dyslexia Association 2002]. DD is regarded as a deficit in the acquisition of
written language (reading, spelling), which is most likely the result from a
deficiency in the recognition and processing of speech sounds (*phonological
deficit*; cf. Snowling 2000). However, recent studies have uncovered a number
of problems in the motor domain as well. Several studies report that compared
to the controls subjects with DD are less stable during a variety of balancing
tasks [Fawcett 1999; Getchell 2007; Moe-Nilssen 2003; Nicolson 1990; Stoodley
2005; Yap and van der Leij 1994] and slower on peg moving [Stoodley 2006a] and
rapid pointing [Stoodley 2006b; Velay 2002]. Implicit motor learning is also
impaired in DD [Howard 2006; Molinari 1997]. In addition, subjects with DD show
disturbances in binocular control, both in tasks that do involve reading [Eden
1994; Stein 1985] and in those that do not [Bucci 2008a,b; Fisher 2000a,b;
Fowler 1991], and they may have abnormal control of saccadic eye movements
[Biscaldi 1998].

The motor abilities tested in the studies mentioned above are known to be
supported, at the neuro-anatomical level, by the cerebellum and are often
regarded as clinical hallmarks of cerebellar disorder [Beldarrain 1999; Gerwing
2005; Ito 2005; Molinari 1997; Petrosini 1996; Yeo 1998]. On the basis of these
facts, researchers have proposed the Cerebellar Deficit Hypothesis (CDH),
according to which DD is associated with a cerebellar deficit [Stoodley 2009a].
The CDH is supported by some structural imaging studies showing that children
and adults with DD have reduced grey matter volume in the anterior cerebellum,
anomalies in metabolite distribution in the right Cerebellum, and diminished
connectivity [Brambati 2004, Brown 2001, Brunswick 1999, Eckert 2003, 2004,
Finch 2002, Laycock 2008, Rae 1998, 2002, Stoodley 2009b,c]. One functional
imaging study reports that implicit motor learning activates different
cerebellar areas in children with DD as compared to control subjects [Menghini
2006]. Two volumetric studies with children / adolescents [Eckert 2003,
Kronbichler 2008] have shown that cerebellar volume is associated with measures
of reading and spelling proficiency. However, no study has tested the
association between cerebellar volume, motor abilities and written as well as
oral language abilities in the same young adults with DD. If the CDH is
correct, it is expected that volumetric cerebellar measures be associated with
the measures of motor and language proficiency in adult subjects with DD.

The objectives of the present study are:
1. To demonstrate that adult subjects with developmental dyslexia have abnormal
cerebellar volume;
2. To demonstrate that abnormal cerebellar volume is associated with language
and motor difficulties.

One part of the study is an observational case-control study. Two groups of
subjects will be tested: a group of 15 young adults with Developmental Dyslexia
(DD) and a group of 15 controls matched for age, sex, and education level. Both
groups will undergo structural MRI, volumetric measurements specifically, and a
battery of behavioral language and motor tests (described in detail in section
4.2). The cerebellar morphometric measures will be compared in the two groups.
The other part of the study is a correlational study, where subjects*
individual cerebellar morphometric measures will be correlated to their
performance on the behavioral language and motor tests.

The study is expected to be carried out within approximately 10 months.
Preparation of MRI facilities and language and motor tasks will take
approximately 2 months. Conducting the experiments will cost 5 months.
Analyzing the data will be completed within 3 months.

There is no burden associated with this investigation. Subjects have to visit
the Utrecht University Medical Center once and lie motionless in the
MRI-scanner for a short amount of time (approximately 30 minutes).