Wobbles, warbles and fish - the brain basis of

dyslexia

Prof John Stein Prof John Stein Oxford Oxford

UniversityUniversity

Supported by The Dyslexia Research Trust (www.dyslexic.org.uk), Dyers & Colourists, Esmee Fairbairn, Garfield Weston and Wellcome

Trusts, BBC Children in Need

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‘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

Reading is difficult!

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

Prevalence of Dyslexia

boys dyslexic boys dyslexic girls girls

girls boys

Reading is 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

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

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.”

Developmental Dyslexia is a complex syndrome- not just readingReading and spelling significantly below that expected

from subject’s age and intelligence, despite good health, teaching and cultural experience

Symptoms• Reading/IQ discrepancy• Visual sequencing problems• Auditory sequencing problems

-poor phonology• Speech impairments (lisps,

spoonerisms, mispronunciations• Very bad spelling• Left/right confusions, mixed

handedness• General sequencing problems• Clumsiness & incoordination –

‘soft’ cerebellar signs

History• Family History (Genetic) of

language, literacy and psychiatric problems

• 20% of all boys.• Difficult birth• Delayed milestones (crawling,

walking, speech)• Developmental dyspraxia, dysphasia

hyperactivity• Autoimmune problems: asthma,

eczema, hayfever• Omega 3 (fish oil) deficiency

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 magnocellularfunction

Reading is primarily a visual process

Visual processing

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

Magnocellular Retinal Ganglion cells keep eyes

still

Visual magnocellular system directs visual attention & eye movements.

The visual magnocellular systemis mildly impaired in dyslexics

• 30% smaller LGN magnocells post mortem

• Reduced and delayed evoked brain waves

• Unstable eye control

• Reduced visual motion sensitivity• Reduced activation of cortical

motion areas (FMRI) • Lower sensitivity to contrast• Lower sensitivity to flicker• Lower stereoacuity• Reduced visual jitter• Weaker visual attention - slower

visual search• Visual crowding• Mini left neglect - clock drawing• Prolonged line motion illusion• Reduced Ternus effect

Abnormal magnocells in dyslexic brain

Delayed Brain Potentials Evoked by Moving Visual Stimulus

• The eyes have to convergefor 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

Vergence control

Magnocellular processing sharpens:

into

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 letters seem to float all over the page”

“The letters move in and out of the page”

“The letters split and go double”

“The c moved over the r, so it looked like another c”

“The p joined up with the c”

“d’s and b’s sort of get the wrong way round”

“The page goes all glary and hurts my eyes”

“I keep on losing my place”

“The words are all tangled up inside my head. I’m confused. I get tangled up in writing the words, and I stop.”

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)

Yellow Filters• Although they do not contribute to

colour vision, retinal magnocellularganglion 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

Yellow filters can improve reading

Increase in literacy in 3 months

0

1

2

3

4

5

6

7

8

reading spelling

mon

ths

yellow

placebo

Blue makes the letters keep still!

Blue filters improved reading even more

Increase in literacy

0

2

4

6

8

10

12

14

reading spelling

mon

ths

blue

placebo

B - Dull Shifting Y - Highly Labile

Blue light

M-system

headache

hypothalamus

Diurnal rhythms

Blue entrains hypothalamus clock

to day length

Blue can also improve headachesDyslexicartist portrays her

migraine!

The colour choice of 297 reading disabled 9 year olds

no colour preference49%

blue 25%

yellow 26%

1

2

3

Reading age increase in 3 months

0

1

2

3

4

5

6

7

8

nil grey normal,readingrecovery

(phonology)

yellow occlusion search blue omega 3sRA

incr

. (m

onth

s)

Elucidating the role of the visual system in reading has enabled us to develop techniques for helping most of the dyslexics we see

*

* *

** **

Magno deficit causes many dyslexics to confuse the visual order of letters!

The auditory/phonological pathway

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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

Meltham Primary School

Det

ectio

n T

hres

hold

(M

od. I

ndex

)

0

1

2

3

0.00

0.04

0.08

0.12

0.16

Det

ectio

n T

hres

hold

(M

od. I

ndex

)

0.000

0.004

0.008

0.012

Dyslexics (N=21) Controls (N=23)

2 Hz FM

240 Hz FM

40 Hz FM

Dyslexics (N=21) Controls (N=23)

p<0.001 p=0.027

p=0.360, N.S.

Controls (N=23)Dyslexics (N=21)

Witton, Talcott, Hansen, Richardson, Griffiths, Rees, Stein & Green, 1998

40 Hz FM

240 Hz FM

2 Hz FM

• Slow frequency changes in speech are tracked in real time by large magnocells in the auditory system

Developmental Dyslexics are less sensitive to changes in sound frequency and intensity –

warbles.

500 Hz pure tone

Many dyslexics also have

phonological problems,

partly caused by auditory

magnocellularimpairments

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

What causes this general

magnocellularimpairment?

GeneticNutrition

• 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

Genetic linkage

C6 KIAA gene controls neuronal migration during early brain development in utero. Downregulationmay explain mismigrationand impaired development of magnocellularneurones

Autoimmune conditions in dyslexics and controls

migraineuveitis

asthma

eczema

allergies

0

5

10

15

20

25

30

1 2 3 4 5

% a

ffect

ed

DyslexicControl

Cod Liver Oil Queue, 1950

‘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

Visual Dyslexia & Diet

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

0

1

2

3

4

5

6

7

8

9

10

n-3 placebo

RA

incr

ease

n-3

placebo

Fish oils, vitamins & mineral supplements reduced offences in Young Offenders by 1/3rd

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Before Supplementation During Supplementation

Rat

io o

f R

ate

of D

isci

plin

ary

Inci

dent

s S

uppl

emen

tatio

n/B

asel

ine

Active

Placebo

Error bars at 2SE to indicate the 95% confidence interval

So fish is indeed good for the brain!

• By increasing membrane flexibility, improves magnocellularresponses

• Help focussing attention, hence improves reading

• Improves self-control, hence reduces violence

• Improves memory (Alzheimer’s)

• Prevents accumulation of Alzheimer’s protein

ConclusionsConclusions

••Fundamental auditory, visual & motor Fundamental auditory, visual & motor temporaltemporalsequencing requirements of speech and reading are sequencing requirements of speech and reading are mediated by mediated by magnocellularmagnocellular neuronal systems in the neuronal systems in the brainbrain••These are impaired in dyslexiaThese are impaired in dyslexia••Treatments that improve mTreatments that improve m-- function improve function improve readingreading•Weak magnocellular function may result from:GeneticGenetic vulnerabilityFatty acid (fish oil)Fatty acid (fish oil) deficiency•These weaknesses cancan be remedied: auditory and phonological training, eye exercises, coloured filters, fish oil supplements

BUT… dyslexia carries talent as well

John SteinJohn Stein

Support The Dyslexia Research Trust

(www.dyslexic.org.uk)

Wobbles, warbles and fish - the magnocellularbrain basis of

dyslexia

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TTT