An fMRI Study of a Dyslexia Biomarker
Berman Sarah
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Cicchino Nicole
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Hajinazarian Ardag
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Mescher Madelyn
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Scott K. Holland
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Horowitz-Kraus Tzipi
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Cincinnati Children's Research Foundation Pediatric Neuroimaging Research Consortium Burnet Ave 3333 Cincinnati
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OH 45229-3039
Dyslexia is a reading disorder that is characterized by slow and inaccurate reading. It affects a significant portion of school age children, who have a higher likelihood for poorer academic performance and lowered self-esteem when suffering from dyslexia. Currently, the diagnosis of dyslexia lacks objective criteria, which can decrease treatment efficacy. Diagnosis relies on a discrepancy between reading ability and intelligence, a measure which can be unreliable. The purpose of this proposed pilot study was to find neural biomarkers for dyslexia using functional magnetic resonance imaging (fMRI), which then can be used in the diagnosis and treatment of the disorder. Two children with dyslexia and two typical readers were given a lexical decision task while being scanned under an fMRI machine. Their scans were then analyzed and compared to typical readers' brain activation using CCHIPS MRI analysis software. The resulting data showed that children with dyslexia had a greater spread of activation during reading tasks and more frontal and occipital activation than typical readers. These data suggest that we can differentiate individuals with dyslexia from typical readers based on their brain activation while reading. These brain differences could be the basis for possible biomar kers of dyslexia.
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INTRODUCTION
Dyslexia is a developmental disorder characterized by slow and
inaccurate word recognition and phonological deficit, which
affects about 7-10% of people across most languages and
cultures (Peterson & Pennington, 2012). Oftentimes, onset of the
disorder becomes apparent during childhood to adolescence and
can be detrimental to academic performance (Ewing & Parvez,
2012). Dyslexia can also have profound negative effects on the
development of self-esteem and self-perception in children
(Humphrey & Mullins, 2002). Students with dyslexia report high
rates of bullying as well as feelings of isolation and exclusion
within academic settings (Humphrey & Mullins, 2002).
The current diagnosis for dyslexia focuses on lower
accuracy and slower reading pace as compared to the expected
level for the age, education, and intellectual abilities of the
individual according to standardized norms (see American
Psychiatric Association DSM-V, 2012). This definition relies on
a discrepancy between intelligence and reading ability in
individuals with dyslexia, even though the discrepancy model
has been criticized for its poor validity (see Cotton, Crewther, &
Crethwer, 2005; Fletcher et al., 1992; Gustafson & Samuelsson,
1999). To date, there is still an ongoing controversy and
variability in the definition of dyslexia, which has led to
significant diversity in the presentation and diagnosis of this
disorder (Cotton, Crewther, & Crethwer, 2005). Furthermore,
the multifaceted mechanisms involved in reading deficits
challenge clinicians and researchers to provide accurate
diagnoses for individuals with reading difficulty. However, there
is no current objective biological marker in the diagnosis of
*To whom correspondence should be addressed:
In order to bring the diagnosis up to a similar level of
objectivity found in other areas of the medical field, there is an
ongoing search for a biological marker of dyslexia (Shapiro,
1999). Functional Magnetic Resonance Imaging (fMRI), which
measures brain activation by tracking the brains blood flow and
volume while performing a cognitive task (Cox, 1996), can be a
possible tool in identifying potential neurobiological
abnormalities in individuals with dyslexia. As with other
neurological impairments (see for example Borovecki, 2005 for
Huntington disease), it allows for a biological analysis of the
brain that is imperative in the search for an objective diagnosis
of dyslexia (Shapiro, 1999).
There is significant evidence, generated by fMRI, that
there are neural differences in individuals with dyslexia as
compared to normal readers. For example, individuals with
dyslexia were found to share abnormalities in the left
hemisphere temporoparietal regions, which are involved in
phonological processing, and left hemisphere occipitotemporal
region, which plays a part in word recognition (Peterson &
Pennington, 2012). Additionally, adults with dyslexia showed
less or no activation in the posterior superior temporal gyrus
(pSTG), which is also involved in phonological processing
(Karni et al., 2005). .
Furthermore, previous MRI research in the field of
dyslexia has pointed at a right lateralized activation in
individuals with dyslexia (Shaywitz et al., 1998). Shaywitz et al.
studied 16-54 years old individuals with dyslexia and 18-63
years old typical readers who were given a non-word rhyming
task. In this task the participant was required to decid (...truncated)