Transcript Template - Dartmouth

Recent Findings in the
Neurobiology &
Neuropsychology of
Reading Processes
A. Maerlender, Ph.D.
Clinical School Services
&
Learning Disorders
Current trends and recent
findings

Neural basis of reading & oral language
 Developmental processes
 Basic sensory processes and
impairments
Visual
 Auditory


General theoretical
ABD (atypical brain development)
 General language impairment
 Tallal’s Hypothesis

2
Normal Reading

Written language is the symbolic code
of oral language behavior

Involves (at least) two physiological
systems:
Audition
 Vision

3
Etiology of Dylsexia

Strong genetic linkage


But no specific gene implicated, rather
a set of genes
Older anatomical data pointing to
disrupted migration of cells and
subsequent cortical ectopias

Felt to reflect disrupted development
and consequent function
4
Current agreement

There is good agreement about the
description of developmental dyslexia

Primarily a problem with sound-symbol
transduction
o
o
o
Difficulty with “phonological awareness”
Subtyping is less than precise
Also problems with rapid access to lexical
material (rapid naming) and a minor
subset of visual-orthographic impairments
5
But still controversy

Some imaging studies show frontal
involvement

Over activation of frontal structures
• See Rumsey, 1997
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Visual Word Processing
(Posner)

Right hem activation



Regular or pseudo letters
Not unique to words or letters
Left hem activation




Extra-striate
More specific to words
‘visual word form’ area
Area develops as child learns to read
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Visual Word Form Area

Medial occipital and temporal lobes

Mostly left

Also a network of left-lateralized areas
 Most posterior for processing letters
 Medial processes orthographically
regular words and nonword strings


Left activation near angular gyrus is a
generalized posterior response to familiar
words as actively processed as language
Not the earliest stage
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Time Course for Processing
During Word Reading
Visual
Features
Primary
Visual
Cortex
Phonology
Eye
Muscles
Motor
Program
Word
Form
Lexical
Semantics
Exec
Attn
Initial
Saccade
Stimulus
ms
0
100
200
300
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Neural systems for
reading

Converging evidence indicates three important
systems in reading, all primarily in the left hemisphere Some right hemisphere activation now implicated;
 These include an anterior system and two posterior
systems:
1) anterior system in the left inferior frontal region;
2) dorsal parietotemporal system involving angular
gyrus, supramarginal gyrus and posterior portions of
the superior temporal gyrus;
3) ventral occipitotemporal system involving portions
of the middle temporal gyrus and middle occipital
gyrus
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Written language neural
pathway

Visual input transmitted from lateral
geniculate to primary cortex in striate
areas and secondary extrastriate
cortex.
 From here 2 streamsVentral (what): unimodal visual area of
fusiform gyrus (may contain ortho reps
of words)
 Dorsal (where): superior parietal lobule
for spatial aspects of reading.

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Reading Areas
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Heteromodal areas

Wernicke’s including angular gyrus,
supramarginal gyrus



Likely responsible for integration of written &
spoken word forms.
Wernicke’s is massively connected to inferior
temporal category specific areas for faces
animals, tools
Also with frontal areas for overt speech production
(Broca’s), and reciprocal connections for memory
and manipulating verbal information.
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Heteromodal areas
SMG
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Neural systems for reading
Shaywitz Study (2002)

Large sample study with fMRI
 Letter judgment, single letter rhyme, word rhyme,
semantic category, line orientation
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Significant differences
between dyslexic and
normal readers

significant differences in brain activation
patterns during phonologic analysis
nonimpaired compared with dyslexic
children.
 nonimpaired children demonstrated
significantly greater activation than dyslexic
children in left hemisphere sites

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Localization of dysfunction
inferior frontal, superior temporal,
parietotemporal, and middle temporal–middle
occipital gyri
and
 right hemisphere sites

o
including inferior frontal, superior temporal,
cingulate, and medial orbital gyri.
 converge
with many reports using
functional brain imaging
17
fMRI Results
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Confirmed two systems for
reading

word analysis

operating on individual units of words such as phonemes,
requiring attentional resources and processing relatively
slowly
o
Parietotemporal area
and

visual word attention

an obligatory system that does not require attention and
processes very rapidly, on the order of 150 msec after a
word is read; Price et al 1996.
o
o
Occipitotemporal area
visual word form area appears to respond preferentially to
rapidly presented stimuli (Price et al 1996) and is engaged
even when the word has not been consciously perceived
(Dehaene et al 2001).
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Frontal system
another reading-related neural circuit
involves an anterior system in the
inferior frontal gyrus (Broca's area),
a region that has long been associated
with articulation and also serves an
important function in silent reading and
naming (Fiez and Frackowiak).
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The relation between
reading and oral language



An intimate connection
Written language is the symbolic form of
oral language
Oral language
Auditory input transmits from
medial geniculate to primary &
secondary areas (superior
temporal gyrus)
 STG may contain auditory
representations of word forms

21
How does reading
develop?

The process of reading involves a
transition from oral language to
symbolic language
22
Specialization of processing
moves from back (lower
level) to front (higher level)



Changes in the neural substrate of auditory and
visual word recognition is associated with
increased specialization.
Specialized processing is performed in in
secondary - unimodal -brain areas for both auditory
and visual input.
Primary perception areas are responsible for lowlevel information processing
23
Reading Development

Older or hi-skill readers activate
orthographic & phonologic info
more quickly than young or low
skill readers
24
Semantic priming

Young/poor readers rely on semantic
priming more than older/skilled readers
Well-developed spelling-sound
mapping allows rapid decoding without
need for semantic cues for word
recognition
 Development relies on automatization
of neural processes

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