Recent Findings in the Neurobiology & Neuropsychology of Reading Processes

1. Recent Findings in the Neurobiology & Neuropsychology of Reading Processes A. Maerlender, Ph.D. Clinical School Services & Learning Disorders

2. 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

3. Normal Reading • Written language is the symbolic code of oral language behavior • Involves (at least) two physiological systems: • Audition • Vision

4. 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

5. Current agreement • There is good agreement about the description of developmental dyslexia • Primarily a problem with sound-symbol transduction • 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

6. But still controversy • Some imaging studies show frontal involvement • Over activation of frontal structures • See Rumsey, 1997

7. 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

8. 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

9. Time Course for Processing During Word Reading Phonology Visual Features Eye Muscles Motor Program Lexical Semantics Primary Visual Cortex Word Form Exec Attn Initial Saccade Stimulus ms 100 0 200 300

10. 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

11. 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.

12. Reading Areas

13. 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.

14. Heteromodal areas SMG

15. Neural systems for readingShaywitz Study (2002) • Large sample study with fMRI • Letter judgment, single letter rhyme, word rhyme, semantic category, line orientation

16. 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

17. Localization of dysfunction • inferior frontal, superior temporal, parietotemporal, and middle temporal–middle occipital gyri and • right hemisphere sites • including inferior frontal, superior temporal, cingulate, and medial orbital gyri. • converge with many reports using functional brain imaging

18. fMRI Results

19. Confirmed two systems for reading • word analysis • operating on individual units of words such as phonemes, requiring attentional resources and processing relatively slowly • 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. • 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).

20. 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).

21. 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

22. How does reading develop? • The process of reading involves a transition from oral language to symbolic language

23. 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

24. Reading Development • Older or hi-skill readers activate orthographic & phonologic info more quickly than young or low skill readers

25. 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