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Wake Forest University
Gallaudet University
Supported by the National Institutes for Child Health and Human Development
Georgetown University
Center for the Study of Learning
http://csl.georgetown.edu
Behavioral Manifestations of Developmental Dyslexia
• Phonological Processing– Sound segmentation and
manipulation– Rapid name retrieval– Verbal working memory
• Sensorimotor Processing– Visual motion processing– Motor coordination– Auditory processing
Behavioral Manifestations of Developmental Dyslexia
• Phonological Processing– Sound segmentation and
manipulation– Rapid name retrieval– Verbal working memory
• Sensorimotor Processing– Visual motion processing– Motor coordination– Auditory processing
Phonological Processing and Reading
• Types of phonological processing (Wagner & Torgesen, 1987)– Phonemic awareness (LAC, Rosner,
CTOPP, spoonerism)– Phonological naming (RAN)– Working memory (Digit Span)
• Subtypes of dyslexia are associated with weaknesses in these types of phonological processes (Wolf 1999)
Behavioral Manifestations of Developmental Dyslexia
• Phonological Processing– Sound segmentation and
manipulation– Rapid name retrieval– Verbal working memory
• Sensorimotor Processing– Visual motion processing– Motor coordination– Auditory processing
Task performance for stimulus velocity detection task in dyslexics and controls
Eden et al., Nature 1996
Visual Motion Perception: Controls versus Dyslexics
Demb et al.,1997 Proc.Nat.Acad.Sci.
Why are there Numerous Behavioral Manifestations in Dyslexia?
• Pan-sensory magnocellular deficit
(Stein 1993)
• Dorsal stream dysfunction
(Eden and Zeffiro, 1999)
• Impaired mapping between sensory modalities (Hari et al., 2002)
• Anomalies in cell migration (Ramus 2004; Galaburda et al. 1985)
Ramus, TINS 2004
Why are there Numerous Behavioral Manifestations in Dyslexia?
• Pan-sensory magnocellular deficit
(Stein 1993)
• Dorsal stream dysfunction
(Eden and Zeffiro, 1999)
• Impaired mapping between sensory modalities (Hari et al., 2002)
• Anomalies in cell migration (Ramus 2004; Galaburda et al. 1985)
Malformations
LeftLeft
RightRight
II
IIII
IIIIII
IVIV
VV
VIVI
Galaburda et al. 1985
Livingstone et al., 1991
Ramus 2004
• Genetically driven focal cortical abnormalities disrupt processes in the left hemisphere (phonological processing)
• Under certain hormonal conditions these disruptions propagate to the thalamus, leading to sensory impairment
• These disruptions also extend to posterior parietal cortex and cerebellum
The neural basis of reading
• Left inferior frontal gyrus
• Left temporo-parietal cortex
• Left infero-temporal cortex
6- 9.4 yn=13
9.4- 18 yn=13
20- 23 yn=15
Reading Activity and Age
Turkeltaub et al. Nature Neuroscience, 2003
Developmental Changes in Activity
p< .001, peak p< .0001Reading Composite
fMR
I
Phonological Processing and Reading
• Types of phonological processing (Wagner & Torgesen, 1987)
– Phonological awareness (LAC)– Phonological naming (RAN)– Working memory (Digit Span)
• Subtypes of dyslexia are associated with these types of phonology
• Are these abilities associated with different brain regions?
Phonological Awareness
Lindamood Auditory Conceptualization Test (LAC)
“Show me /p/ /t/ /p/”
“If this says ‘eth’,show me ‘ith’
Phonological Naming
Rapid Automatized Naming Test (RAN)
s a o d o p a p d s o s p s d a o a a s p d o d s so p s p d o s a o d a p da d o p s p a s d o d s ap o s d s p o a o d a p s
s a o d o p a p d s o s p s d a o a a s p d o d s so p s p d o s a o d a p da d o p s p a s d o d s ap o s d s p o a o d a p s
Phonetic recoding in working memory
Digit Span
“3 8 2 4”“7 4 6 2 5”
“9 2 3 6 1 8”“5 3 8 2 7 4 6”
“2 5 4 3 2 8 9 4”
Correlations with Phonological Processing
Phonological AwarenessPhonological RecodingWorking Memory
p< .005, peak p< .0005
Turkeltaub et al. Nature Neuroscience, 2003Turkeltaub et al., Nature Neuroscience 2003
Activation Likelihood Estimate
Objective assessment of the consistency of findings in neuroimaging in studies of aloud reading
Included studies:Typical adultsReading of real wordsTotal of 11 studies
Aloud Word Reading in Adults
Meta-Analysis of 11 PET Studies
fMRI(n=32)
p<.001 p<.0001
Turkeltaub et al 2002
Flowers, Wood, & Naylor, 1991
Non-Dyslexics: Dyslexics:
Real word reading Real word reading
Non-Dyslexics: Dyslexics:
Pseudoword reading Pseudoword reading
Neural Basis ofPseudoword Reading in Dyslexia
Flowers et al., A. Neurol., in press
Activation Likelihood Estimate
Objective assessment of the consistency of neuroimaging findings in developmental dyslexia
Studies of reading and phonological processing
Spatial coordinates from nine papers (14 experiments)
2 two Activation Likelihood Estimate (ALE) meta-analyses to identify regions most likely exhibiting: D>C and C>D
Criteria for Inclusion in ALE Meta-Analysis
• Paradigms involved processing of visually presented words, pseudowords or letters in the subjects’ native, alphabetic language.
• Participants were post-pubertal teens and adults.
Papers included in the MA
1 Paulesu 1996 decision (rhyme)2 Grünling 2004 decision (rhyme)3a Rumsey 1997 decision
(phonological/orthographic)3b explicit
(phonological/orthographic)4a Brunswick 1999 decision (ascender)4b explicit (reading)5 Paulesu 2001 explicit/decision6 Georgiewa 1999 explicit/transformation7 Ingvar 2002 explicit reading8 McCrory 2005 explicit reading9 Flowers 2005 explicit reading
Maisog et al, under review
Results
• Dyslexic readers are most likely to underactivate posterior and anterior portions of the left hemisphere as well as posterior portions of the right hemisphere.
• Dyslexic readers are likely to overactivate right insular cortex and right thalamus.
• The most robust findings were left temporal parietal, left extrastriate, and right superior temporal hypoactivity and right anterior insula hyperactivity in dyslexic individuals.
Typical Readers Dyslexic Readers
Brain Briefings, Society for Neuroscience
Neurobiological Basis of Dyslexia
• Reading and phonological processing involve left hemisphere perisylvian regions.
• The neurobiological representation of these regions is established early on and relies on regions that process information from multiple sensory modalities.
Overall Summary
•Dyslexic individuals show anomalous activity in these regions, especially occipito-temporal (ventral) and parietal (dorsal) cortex.
Overall Summary
• Merge the well characterized language based problems observed in dyslexic individuals with sensorimotor manifestations
• Study these processes in other writing systems
Future Studies
John AgnewKate CappellEmily CurranEmma ColeIain DeWittErin EinbinderLynn GareauKaren JonesJessica KoehlerDaniel KooJoe MaisogMartha MirandaAlison MerikangasCorinna MooreEileen NapolielloJenni RosenbergPeter TurkeltaubRobert TwomeyJohn VanMeterThomas Zeffiro
Wake Forest UniversityLynn FlowersFrank WoodDebi Hill
Gallaudet UniversityCarol LaSassoKelly Crain
Supported by NICHD, NIDCD, NIMH
http://csl.georgetown.edu
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