Wobble, Warbles and Fish: the brain basis of dyslexia


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John Stein, Professor of Neuro-Physiology in the University of Oxford; Chairman Dyslexia Research Trust.

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Wobble, Warbles and Fish: the brain basis of dyslexia

  1. 1. Prof John Stein Oxford University Wobbles, warbles and fish - the brain basis of dyslexia D Supported by The Dyslexia Research Trust (www.dyslexic.org.uk), R Dyers & Colourists, Esmee Fairbairn, Garfield Weston and Wellcome Trusts, BBC Children in Need T
  2. 2. Reading is difficult! ‘Reading is a painful task. It extinguishes the light from the eyes. It bends the back. It crushes the viscera and the ribs. It brings forth pain to the kidneys and weariness to the whole body.’ 13th C. Florentine monk or 20th C dyslexic! ‘Writing is not merely a copy of speech; it is tyrannical, unnatural, perverse, pathological and sinful’. Jacques Derrida –founder of structuralism, 1950
  3. 3. Reading is difficult because it requires: 1. Rapid visual identification of letters and their order; even in experienced good readers this process is rate limiting 2. Rapid auditory translation into the sounds they stand for 3. Background knowledge of ‘phonology’- how words can be split down into separate sounds - phonemes All these processes depend on the timing properties of magnocellular neurones
  4. 4. Reading is Prevalence of Dyslexia difficult! 1 in 3 of US & UK 11yr olds leave primary school unable to read properly This is cruelty; they cannot cope with high school; they lose all self confidence girls boys Reading failure is the commonest cause of childhood misery, depression, even suicide Commonest disability among College students OR frustration, aggression, crime; 75% of those in gaol are illiterate. Nevertheless, if they survive school, dyslexics are often highly talented – original, artistic, entrepreneurial boys dyslexic boys dyslexic girls girls
  5. 5. The Hurt of Dyslexia “I am in the slow readers’ group. My brother is in the football team My sister is a server. My little brother was a wise man in the Christmas play. I am in the slow readers group. That is all I am in. I hate it.”
  6. 6. Developmental Dyslexia is a complex syndrome- not just reading Reading and spelling significantly below that expected from subject’s age and intelligence, despite good health, teaching and cultural experience Symptoms History • Reading/IQ discrepancy • Family History (Genetic) of • Visual sequencing problems language, literacy and psychiatric • Auditory sequencing problems problems -poor phonology • 20% of all boys. • Speech impairments (lisps, • Difficult birth spoonerisms, mispronunciations • Delayed milestones (crawling, • Very bad spelling walking, speech) • Left/right confusions, mixed • Developmental dyspraxia, dysphasia handedness hyperactivity • General sequencing problems • Autoimmune problems: asthma, • Clumsiness & incoordination – eczema, hayfever ‘soft’ cerebellar signs • Omega 3 (fish oil) deficiency
  7. 7. 2/3rds of backward readers complain of visual difficulties with reading. Often their eyes wobble when they try to read. This may be due to weak visual magnocellular function
  8. 8. Reading is primarily a visual process Visual processing
  9. 9. Magnocellular Retinal Ganglion cells keep eyes still Large magnocellular cells (100x p- cells in area) – are for timing visual events: fast responses, sensitive to low contrast, motion, flicker, for focussing visual attention and controlling eye movements Most retinal ganglion cells are parvocellular (small): for colour, fine detail, high contrast
  10. 10. Visual magnocellular system directs visual attention & eye movements.
  11. 11. The visual magnocellular system is mildly impaired in dyslexics • Reduced visual motion sensitivity • 30% smaller LGN • Reduced activation of cortical magnocells post motion areas (FMRI) • Lower sensitivity to contrast mortem • Lower sensitivity to flicker • Reduced and • Lower stereoacuity delayed evoked • Reduced visual jitter • Weaker visual attention - slower brain waves visual search • Visual crowding • Unstable eye control • Mini left neglect - clock drawing • Prolonged line motion illusion • Reduced Ternus effect
  12. 12. Abnormal magnocells in dyslexic brain
  13. 13. Delayed Brain Potentials Evoked by Moving Visual Stimulus
  14. 14. Vergence control • The eyes have to converge for near vision when reading • Control of vergence eye movements is dominated by the visual magno system • The vergence eye movement control system is the most vulnerable to drugs and disease • Dyslexics have very unstable vergence control
  15. 15. Magnocellular processing sharpens: into
  16. 16. Weak magnocellular system causes unstable vision - oscillopsia “The letters go all blurry” “The letters move over each other, so I can’t tell which is which” “The words are all “The letters seem to float all over the page” tangled up inside “The letters move in and out of the page” my head. I’m “The letters split and go double” confused. I get “The c moved over the r, so it looked like another c” tangled up in “The p joined up with the c” writing the words, “d’s and b’s sort of get the wrong way and I stop.” round” “The page goes all glary and hurts my eyes” “I keep on losing my place”
  17. 17. Interventions that improve m- function and eye control often improve reading In some children with poor eye control temporary blanking of left eye improves vergence control and reading by 2 months/m (proved by randomised controlled trials –RCT) In older children exercises can stabilise binocular fixation and greatly improve reading (proved by RCT) Yellow or blue coloured filters can often rebalance visual M- input and greatly improve reading (av. 2 ms/m -proved by RCTs)
  18. 18. Yellow Filters • Although they do not contribute to colour vision, retinal magnocellular ganglion cells are most responsive to yellow light • So in some children yellow filters can increase magnocellular and visual motion sensitivity and binocular control, hence improve reading
  19. 19. Yellow filters can improve reading Increase in literacy in 3 months 8 7 6 5 months yellow 4 placebo 3 2 1 0 reading spelling
  20. 20. Blue makes the letters keep still!
  21. 21. Blue filters improved reading even more Increase in literacy 14 12 10 months 8 blue 6 placebo 4 2 0 reading spelling
  22. 22. Blue entrains hypothalamus clock headache to day length hypothalamus Blue light Diurnal rhythms M-system B - Dull Shifting Y - Highly Labile
  23. 23. Blue can also improve headaches Dyslexic artist portrays her migraine!
  24. 24. The colour choice of 297 reading disabled 9 year olds yellow 26% no colour preference 49% 1 2 3 blue 25%
  25. 25. Elucidating the role of the visual system in reading has enabled us to develop techniques for helping most of the dyslexics we see Reading age increase in 3 months 8 ** 7 ** 6 RA incr. (months) 5 * * 4 * 3 nil grey normal, yellow occlusion search blue omega 3s 2 reading recovery 1 (phonology) 0
  26. 26. Magno deficit causes many dyslexics to confuse the visual order of letters!
  27. 27. D The auditory/phonological R pathway T
  28. 28. Hearing differences between letter sounds requires sensitivity to changes in frequency and intensity 2nd and 3rd formants ascend in frequency for ‘b’; but descend for ‘d’. Test sensitivity to warbles
  29. 29. Meltham Primary School
  30. 30. Developmental Dyslexics are less sensitive to changes in sound frequency and intensity – warbles. • Slow frequency changes in speech are tracked in real time by large magnocells in the auditory system 2 Hz FM 40 Hz FM 3 0.16 Detection Threshold (Mod. Index) 2 Hz FM 40 Hz FM p<0.001 p=0.027 0.12 2 0.08 500 Hz 1 0.04 pure 0.00 tone 0 Dyslexics (N=21) Controls (N=23) Dyslexics (N=21) Controls (N=23) Detection Threshold (Mod. Index) 240 Hz FM 0.012 p=0.360, N.S. 240 Hz FM 0.008 0.004 0.000 Dyslexics (N=21) Controls (N=23) Witton, Talcott, Hansen, Richardson, Griffiths, Rees, Stein & Green, 1998
  31. 31. Many dyslexics also have phonological problems, partly caused by auditory magnocellular impairments
  32. 32. Auditory and visual magnocellular sensitivity determines over half of the differences in children’s reading ability The most important determinant of overall reading ability is magnocellular neuronal sensitivity. Encouraging because this can be improved
  33. 33. What causes this general magnocellular impairment? Genetic Nutrition
  34. 34. Genetic linkage • Are particular genes associated with poor reading? • Analyse the DNA of father, mother and their dyslexic and normally reading children • 400 Oxford families • EU consortium; 1000 families, 2000 cases, 2000 controls, 50,000 markers per case
  35. 35. C6 KIAA gene controls neuronal migration during early brain development in utero. Downregulation may explain mismigration and impaired development of magnocellular neurones
  36. 36. Autoimmune conditions in dyslexics and 30 controls allergies 25 20 % affected 15 Dyslexic eczema Control 10 asthma 5 uveitis migraine 0 1 2 3 4 5
  37. 37. Cod Liver Oil Queue, 1950
  38. 38. ‘Most Britons were better fed in 1943 than in today’ Dr Hugh Sinclair, Magdalen College, Oxford • Aged 28, he persuaded the WWII government to provide free cod liver oil and orange juice to all pregnant mothers and young children • 20% of the brain consists of omega-3s, mainly DHA • Essential for flexible membranes – rapid neural responses • Modern diet very deficient in fish oil omega–3s
  39. 39. Visual Dyslexia & Diet
  40. 40. Durham study - Omega 3 EPA supplements helped dyspraxic children to improve their concentration and their reading (RCT – Richardson & Montgomery) Increase in Reading age in 3 months 10 9 8 7 RA increase 6 n-3 5 placebo 4 3 2 1 0 n-3 placebo
  41. 41. Fish oils, vitamins & mineral supplements reduced offences in Young Offenders by 1/3rd Ratio of Rate of Disciplinary Incidents Supplementation/Baseline 1.4 Active 1.2 Placebo 1 0.8 0.6 0.4 Error bars at 2SE to indicate the 95% confidence interval 0.2 0 Before Supplementation During Supplementation
  42. 42. So fish is indeed good for the brain! • By increasing membrane flexibility, improves magnocellular responses • Help focussing attention, hence improves reading • Improves self-control, hence reduces violence • Improves memory (Alzheimer’s) • Prevents accumulation of Alzheimer’s protein
  43. 43. Conclusions •Fundamental auditory, visual & motor temporal sequencing requirements of speech and reading are mediated by magnocellular neuronal systems in the brain •These are impaired in dyslexia •Treatments that improve m- function improve reading •Weak magnocellular function may result from: Genetic vulnerability Fatty acid (fish oil) deficiency •These weaknesses can be remedied: auditory and phonological training, eye exercises, coloured filters, fish oil supplements BUT… dyslexia carries talent as well
  44. 44. Wobbles, warbles and fish - the magnocellular brain basis of dyslexia John Stein Support D The Dyslexia Research Trust R (www.dyslexic.org.uk) T