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ctional and structural brain abnormalities in developmental dyslexia: The role of the cerebellum and occipitotemporal lobe
Clare Shakeshaft, Cathy Price & HweeLing Lee
Introduction
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Anchor
Background
Ship
Truck
• Impairments in development dyslexia are not confined to reading and literacy
skills. Additional behavioural deficits include phonological processing, motor skills
and automatic balance. These difficulties are not observed consistently and vary
from individual to individual.
• Do some dyslexics have multiple impairments at the neurological level? Or
might there be a single causal mechanism that accounts for all problems?
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Cup
Axe
Slide
Functional Imaging Studies
•Many areas of abnormal activation observed (including cerebellum), but not
consistent across studies and usually confounded by task performance differences.
4a
Fig. 2. Stimuli used for Exp. 2. (1a)
Semantic decisions on Words (1b)
Perceptual decisions on triads of
meaningless symbols; (2a)
Semantic decisions on Pictures;
(2b) Perceptual decisions on triads
of meaningless non objects; (3a)
Reading aloud Words; (3b) Saying
“one, two three” to triads of
meaningless symbols; (4a) Naming
aloud Pictures; (4b) Saying “one,
two three” to triads of meaningless
non objects
Exp 1: Structural Scan
Method
Method
•Are differences in brain activation are observed in the same regions that show
differences in brain structure?
•Subjects indicated the position of four black dots in a simple music note reading
task that did not involve phonological or semantic processing.
•Vocal and manual responses were made with corresponding baseline conditions.
Fig 5. Stimuli used for music
reading task in activation
condition (left) and baseline
condition (right).
4b
•Left occipito-temporal cortex abnormalities are observed during both reading and
picture naming (McCrory et al., 2005) when task performance difficulties explicitly
controlled.
•It is important to investigate other neural substrates that may contribute to
impairments that manifest behaviourally in dyslexia, such as the cerebellum
(Nicolson et al., 1999).
Exp 3: Music Reading Task
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Results
Both dyslexics and controls activated the same cerebellar region found to be
structurally abnormal in Exp.1.
Results
1) The same midline cerebellar region was activated during reading in dyslexics and
controls as reported in Exp. 1.
Fig. 6. Activation in
sensori-motor
integration in the
same region of the
cerebellum (yellow)
as Exp 1.
•Do dyslexic individuals show differences in brain structure relative to age matched
controls without reading difficulties?
Fig. 3. Reading activation in
both groups at the same
coordinates of the structural
abnormality in the same
midline cerebellar region
•34 dyslexic subjects and 17 controls scanned using a whole brain unbiased
objective technique, voxel based morphology (VBM).
Results

Structural analyses revealed grey matter density increased with spelling ability
in a region of the midline cerebellum.
Fig 1. Localisation of
reduced grey matter
density in a midline
cerebellar region when
correlated with spelling
(comparisons across all
subjects)
2) Dyslexics showed reduced activation relative to controls in the right occipitotemporal cortex during all tasks, irrespective of whether the stimuli were
meaningful and meaningless.
3) Reduced activation in the dyslexic group relative to the controls in the left
occipito-temporal cortex for naming and semantic tasks with meaningful stimuli
only.
Fig. 4. Reduced activation in dyslexics relative
to the controls in right fusiform gyrus for all
perceptual and semantic tasks with meaningful
and meaningless stimuli (red). Reduced
activation in the dyslexic group relative to
controls in the left fusiform gyrus for naming
and semantic tasks with meaningful stimuli
only (yellow).
This shows a region of the cerebellum whose structure reflects spelling ability.
Exp 2: Reading, Naming & Semantic Decisions
• This study shows structural abnormalities in a region of the cerebellum that
may mediate spelling and reading ability in developmental dyslexia.
• Structural abnormalities in this cerebellar region are associated with sensorimotor integration.
• Functional abnormalities are reported in the left occipito-temporal cortex for
meaningful stimuli only, therefore this region is not specific to phonology.
• Impaired phonological abilities in dyslexic behaviour may reflect a more
general deficit in sensori-motor integration.
Selected References
1] McCrory, E., Mechelli, A., Frith, U., and Price, C., (2005) More than words: A
common neural basis for words and naming deficits in developmental dyslexia?
Brain, 261-267.
Method
•Only subjects with accuracy of 85% and over in naming condition included
in analyses, resulting in 20 dyslexics and 14 controls.
Activation in this area reflects non-verbal sensori-motor integration.
Summary
Conclusion
•Subjects scanned during word reading, picture naming, semantic decisions
on written words or pictures of objects and perceptual decisions on
meaningless non-objects or symbols.
Conclusion
Conclusion
The deficit observed in the occipito-temporal region is not specific to phonology.
2] Nicolson, R.I., & Fawcett, A.J., Berry, E.L., Jenkins, I.H., Dean, P., & Brooks, D.J.
(1999) Association of abnormal cerebellar activation with motor learning difficulties
in dyslexic adults. Lancet, 353, 1662-1667.