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