Recent Findings in the Recent Findings in the Neurobiology & Neurobiology &

Neuropsychology of Neuropsychology of Reading ProcessesReading Processes

A. Maerlender, Ph.D.Clinical School Services

& Learning Disorders

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Current trends and recent Current trends and recent findingsfindings

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

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Normal Reading

Written language is the symbolic code of oral language behavior

Involves (at least) two physiological systems: Audition Vision

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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

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Current agreementCurrent agreement

There is good agreement about the description of developmental dyslexia Primarily a problem with sound-symbol

transductiono Difficulty with “phonological awareness”o Subtyping is less than preciseo Also problems with rapid access to lexical

material (rapid naming) and a minor subset of visual-orthographic impairments

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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 Time Course for Processing During Word ReadingDuring Word Reading

0 300100 200

Stimulus

PrimaryVisualCortex

VisualFeatures

WordForm

MotorProgram

ms

ExecAttn

LexicalSemantics

Phonology

EyeMuscles

InitialSaccade

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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 streams- Ventral (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

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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 Occipitotemporal areao 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 The relation between reading and oral languagereading and oral language

An intimate connectionAn intimate connection Written language is the symbolic form of Written language is the symbolic form of

oral languageoral language Oral language

Auditory input transmits from medial geniculate to primary & secondary areas (superior temporal gyrus)

STG may contain auditory representations of word forms

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How does reading develop?

The process of reading involves a transition from oral language to symbolic language

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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 low-level information processing

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Reading DevelopmentReading Development

Older or hi-skill readers activate orthographic & phonologic info more quickly than young or low skill readers

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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