CAUSES:

Neurological Basis:

• Missing neurological connections between certain regions of the brain — particularly the link between the occipital and parietal lobes of the brain (angular gyrus)
• As shown through the Orton Dyslexia Society's Brain Bank (where individuals with well documented cases of dyslexia donated their brains to research)
  • Very little correlation between brain size and IQ but certain regions of the brain (language centers, frontal lobe are subtly larger in those without dyslexia)
  • Individuals with dyslexia have brain functions different than those without
    • First study (1980): Frank Duffy used brain measurement techniques which have since been replaced — significant difference in kids with LD and those who don’t
      • Where he went wrong: He believed that, at the end of the decade (1990), all schools would use this to diagnose
      • At a group level, this was correct! But overlap is so great, so you can’t use this in a diagnostic manner (only sure bets are ones at an extreme level)
• Systematic differences between neurons (fewer neural connections in people with dyslexia -- decreased performance)
• Anatomical differences in terms of number of connections and degree of specialization (and laterality) in brain
  • For almost all right handed, left hemisphere controls language
  • For left handers, less clear distinction (50% more likely to be diagnosed with LD than right handed)

Heritable basis:

• If you have a LD, 50% of your first order relatives [siblings, parents, children — one generation in either direction] will also have significant difficulties in learning. These difficulties may not necessarily be formally diagnosed, but they might have struggled in the same sort of way.
• If you and your parents share this difficulty, the LD could be exacerbated by habits:
  • Parents might be too embarrassed to read to their children because of their own reading difficulties
  • Less books in the home (because parents don't read themselves)
  • Overall, less exposure to language!
• Sizable portion can be explained by genetics

Other causes include:

• Difficulty during childbirth increases risk of LD: kids who have the umbilical cord around their neck (lack of oxygen) during delivery
• Presence of toxins in the household (ex. lead — EPA banned it in gas/paint in the 1970s)

CAUSES OF LEARNING DISABILITIES:

• Always an assumption of neurological impairment, now we can put a finger on what specifically
• Prenatal development
  • Use of drugs/alcohol during pregnancy
  • Any sort of illness during pregnancy/postnatal weeks
• Prenatal health care (associated with poverty which is a predictor)
  • Low birth weight/multiple births (quadruplets, septuplets) is correlated quite highly (correlation between low birth weight and being born premature)
  • Using forceps during birth is correlated
  • Anything related to noxia (lack of oxygen) associated with later LD
• Hard neurological signs: perform within limits on neurological tests
• Soft neurological signs: most people could never tell except neurologists (most of us have a swirl on top of head, kids with neurological disabilities tend to have 2 center points; index finger longer than ring finger)
• Very substantial difference (barely 5 years old and almost 6 years old are very different in development) in readiness for learning depending on age at entry date to kindergarten
  • Youth hockey players (NHL): more playing Jan, Feb, March than other months
  • Kindergarten used to be about socialization (not really education)
  • A lot of debate about when’s the optimal age to start teaching reading/writing