General and Specific Cognitive Abilities

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General and Specific Cognitive Abilities
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Cognitive Abilities

• Specific cognitive abilities
• E.g., verbal ability, spatial ability, memory,
  speed of processing
• General cognitive ability (g)
• Often used to be called intelligence

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Hierarchical Models

• Very prevalent in cognitive sciences
• Work on the premise of interconnected levels
• Different units in each level
• Specific units might interconnect within and
  between levels

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Hierarchy of Cognitive Ability
General cognitive ability (g)
Specific cognitive ability
Individual tests
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Interactions

• Hundreds of individual psychological tests used
  in assessment
• Moderate correlation between performance on
  different specific cognitive abilities
• E.g., do well on spatial, probably do well on
  memory

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Correlations

• Not empirical correlation is not causation
• Correlations can not tell why/how one factor
  relates to another, just the degree to which they
  do (or do not)

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Genetic Regulation

• Not really much question that there is
  heritability involved in cognitive ability
• Specific gene and environmental control, however,
  is still pretty much unknown in humans
• Better understanding in nonhumans
• Empirical testing can be conducted

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Intelligence Testing

• Various intelligence (IQ) tests
• Alfred Binet
• Identify students needing special help
• First test, 1905
• Revised to Binet-Simon (1908, 1911), then
  Stanford-Binet (1916)

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Studies in Human Intelligence

• Early adoption studies (Burks 1928 Leahy 1935)
• IQ correlates higher in nonadoptive families than
  in adoptive families
• Adopted away childrens IQ correlates with their
  biological parents (Skodak Skeels 1949)
• This is increasingly true as child ages
• 1960 Louisville Twin Study, longitudinal study of
  environment and genetic effects begun

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Heritability and Intelligence Correlations

• First degree relatives, 0.45
• Adopted away children and biological parents,
  0.25
• Sibs adopted apart, 0.25
• MZ, 0.85
• DZ, 0.6
• MZ raised apart, 0.75

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Couple Complications to This

• Assortative mating
• Nonadditive genetic variance

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Assortative Mating

• Non-random mating when mates have similar
  features/characteristics
• Important for our discussion
• Affects estimates of heritability
• In first-degree relatives can inflate
  heritability
• E.g., sibs are more similar in trait because
  parents are similar for same trait
• In twins, though, can underestimate heritability
• Raises DZ correlations because theyre 1st degree
  relatives, so lessens difference b/t MZ and DZ
  twins

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Nonadditive Genetic Variance

• Additive genetic effects
• Alleles at locus and across loci add up
• Nonadditive effects
• Effects of alleles different in presence of other
  alleles
• Dominance
• Alleles at same locus interact
• E.g., heterozygous phenotype different from
  homozygous dominant phenotype
• Epistasis
• Alleles at different loci interact to affect
  behaviour phenotype of different genes
  suppressed or expressed
• Emergenesis
• Epistatic effects producing extraordinary
  effects wont be heritable due to interactive
  nature

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General Intelligence

• Charles Spearman
• Schoolchildrens grades across unrelated subjects
  positively correlated
• Proposed general intelligence
• Initial interpretation that variation in
  intelligence due to
• Factor specific to an individual mental task
• A general factor, g, that governs performance on
  all cognitive tasks
• Ignored group factors, however need factor
  analysis to identify this

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g-Factor

• Is g real?
• What is the actual interaction between specific
  and general cognition?
• Correlations

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g-Loading

• Tests of cognitive ability derive most of their
  validity from the extent to which they measure g
• g-loaded if quantifiable measure(s) of a task
  correlate highly with g
• Primary goal of IQ tests is to create reliable
  and valid tests thus, the tests tend to be
  intentionally g-loaded

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Non-specificity

• However, g not specific to any particular domain
  of knowledge or mental skill
• Also, seems independent of cultural content
• Support idea that g is real and not simply an
  artifact of particular opportunities to learn
  specific skill sets

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Biological Correlates

• Brain size correlate with g, 0.4
• Various brain wave activity and g, 0.5-0.7
• Speed of nerve conduction with g, 0.4
• Even elementary cognitive tasks (ECTs) correlate
  with g (tasks like identify the colour of a
  light, number of figures on a page, etc.)

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g

• g widely accepted
• Seems to have moderate to high heritability
• That said, less clear what g really is
• Single general process?
• E.g., information processing speed, executive
  function
• Interaction/intersection of specific cognitive
  functions?
• Frequently, g used synonymously with
  intelligence

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QTL and g

• Highly likely that many separate components
  contribute
• Polygenic
• Environment
• Effect at what level?
• Elementary properties, specific cognitive
  ability, general cognitive ability

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Top down

• Genes act directly on g
• E.g., perhaps through neural activity speed, etc.

General cognitive ability
Genes
Specific cognitive abilities
Elementary processes
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Bottom Up

• Genes affect each basic element of information
  processing
• Highly reductionistic model

General cognitive ability
Specific cognitive abilities
Genes
Elementary processes
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Multi-level Interaction

• Unique genetic effects at each level, but also
  genetic effects in common across levels

General cognitive ability
Genes
Genes
Specific cognitive abilities
Genes
Elementary processes
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Evidence

• Some support for top down
• Modularized view of brain function would fit well
  with bottom up
• However, multivariate genetic analysis supports
  multi-level interaction
• Keep in mind, this model incorporates elements
  from both top down and bottom up

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Non-human Animal Models

• Can look for g-like abilities in non-humans
• Look for specific cognitive abilities that are
  directly comparable across species (e.g., spatial
  ability)

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Maze Dull/Maze Bright

• Tolman and Tyron
• Selectively bred rats for ability in maze
  learning
• Maze bright rats showed few errors, maze dull
  rats many errors after few generations

Maze dull
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Mean Errors
Maze bright
0
1
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Generations
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Heritability for Learning

• Inbred strains of mice

Bovet et al. (1969)
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Heritability in Learning
Bovet et al. (1969)

• In and of itself, not that novel, unexpected,
  surprising
• But, environmental effects can come in

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Genotype-Environment Interaction

• Cooper Zubek (1958)
• Enriched, restricted, standard lab conditions
• Enriched improves MD, not MB
• Restricted detrimental to MB, not MD

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Popularity of Mice

• Mouse genome
• Can test for specific gene effects
• E.g., transgenic critters
• Very useful for genotype-environment interactions
  with respect to cognitive abilities
• Obviously, more difficult in humans, but starting
  to get there

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Caspi et al. (2007)

• Childrens intellectual development
• Interaction of genetic and environmental
  experience
• Breastfeeding
• IQ scores

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Breastfeeding

• Long-chain polyunsaturated fatty acids (LC-PUFAs)
• Present in human milk, absent in cows milk
• Specifically, DHA (docosahexaenoic acid) and ARA
  (arachidonic acid)
• Required for efficient neurotransmission, neurite
  outgrowth, dendritic arborization, and neuron
  regeneration post cell injury
• DHA and ARA accumulate in human brain in early
  postnatal months
• Higher concentrations in breastfed than formula
  fed infants

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Effect on IQ

• Breastfed children have higher IQs than
  non-breastfed children
• Effect persists into adulthood
• Not due to SES or other culture-specific factors
• Important to control for, as in Western
  countries, higher SES is related to higher IQ,
  and higher SES women are more likely to breastfeed

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Non-human Animal Models

• Animals deprived in n-3 fatty acids show neuronal
  deficits in memory, sensory, and visual abilities
• DHA supplementation in rodents and nonhuman
  primates increases DHA concentrations enhances
  performance on learning, memory, and problem
  solving tasks

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FADS2

• Chromosome 11 candidate gene
• Role in modification of dietary fatty acids
• Encodes delta-6 desaturase, the rate limiting
  step on the metabolic pathway for ARA and DHA
  production
• Hypothesis cognitive advantage of breastfeeding
  related to genetic differences in LC-PUFA
  metabolism, specifically at FADS2

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Markers and Subjects

• Used two SNPs
• Genetic polymorphisms rs174575 and rs1535
• Strong linkage disequilibrium through promoter
  and intragenic region of FADS2 (and also FADS1,
  another gene involved in fatty acid metabolism)
• Over 1000 New Zealand children born 1972-73, IQ
  measures at age 7, 9, 11, 13
• Over 2200 children from British twins born
  1994-95 IQ measured at age 5

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IQ Outcomes and Genotype
110 105 100 95 90
New Zealand Cohort
British Cohort
Mean IQ
CC CG GG CC CG GG Genotypes
Not breastfed
Breastfed
Overall, breastfed children had IQ scores 5.6 and
6.3 points higher than non-breastfed children in
New Zealand and British cohorts, respectively.
About 90 either CC or CG.
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Genotype and IQ

• Dominant effect of C allele in response to
  breastfeeding
• New Zealand breastfed children with C allele
  showed 6.4 IQ-point advantage (plt0.001) compared
  to non-breastfed children GG homozygotes gained
  no advantage from breastfeeding
• British breastfed children with C allele showed
  7.0 IQ-point advantage (plt0.001) GG had no
  advantage from breastfeeding
• Averaging, this equates to a 6.8 IQ point
  advantage, or 0.48 standard deviation units in
  the general population

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rs174575

• Genetic moderation of breastfeeding effects on IQ
  not likely directly due to rs174575
• Actual molecular mechanism of influence by
  rs174575 is currently unknown
• May be that rs174575 influences biosynthesis of
  LC-PUFAs from dietary precursors, possibly
  through increased transcriptional activity

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Application

• Earlier studies looking at neurodevelopment of
  infants fed DHA-supplemented vs. unsupplemented
  formula
• Results inconclusive
• Current research may offer explanation genetic
  heterogeneity in fatty acid metabolism may dilute
  supplemental effects

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Application

• FADS2 locus has not appeared on the first
  genome-wide scans for intelligence
• Such scans identify genes with associations with
  phenotypes regardless of participants
  environments ineffective for detecting genes
  whose effects are conditional on environmental
  exposure
• In contemporary Western samples, significant
  portion of population is not breastfed this
  would conceal link between FADS2 variation and IQ

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Heritability and Maturation

• Early twin studies investigated development
  (e.g., Galton, 1876 Merriman, 1924)
• Heredity increasingly important as you develop

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Developing Twins
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Why

• New genes come into effect
• Positive feedback effect
• IQ increase when adopted by parents with high IQ
• Intellectual experience more self-directed as an
  adult
• Shared environment effects decrease with age

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Genetic Contributions to Developmental Change

• g is pretty stable, not perfectly so if change
  happens, it has a genetic aspect
• Genetic effects seem to act at transitional ages
• Infancy to early childhood (e.g., language
  acquisition)
• Early to middle childhood (e.g., theory of mind)
• Etc.

Gen. factors New gen. factors New gen. factors
Infancy Early childhood Middle childhood
Shared Env.
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Environment Specific Cognition

• Scarr Weinberg (1978)
• Adoption study
• Little similarity for adoptive parents and
  adopted children or between adopted siblings on
  specific subsets of intelligence test except
  vocabulary
• Like g, specific cognitive abilities also little
  influenced by shared environment (i.e.,
  heritability significant factor)

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Academic Performance

• Achievement vs. ability
• Semantics?
• Shared environment 60, heritability 30 (for
  6-12 year range)
• Heritability effect does increase, and
  environment effect decreases with age

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Heritability and Subjects
From Grade 7 Report Card Grades
From High School Achievement Tests
Twin Correlations Subject MZ DZ
History .80 .51 Reading
.72 .57 Writing .76 .50 Arithmetic
.81 .48
Twin Correlations Subject
MZ DZ Social .69 .52 Natural Sciences
.64 .45 English use .72 .52 Mathematics
.71 .51
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School Achievement g?

• Multivariate genetic analysis shows a common
  genetic effect explains much of the correlation
  between scores in different domains (i.e.,
  subjects)
• Is this g, or some other measure?
• Some-to-much of this is g, but some is
  achievement specific
• Implies that achievement scores (within normal
  range) that are not due to ability are largely
  due to environment

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Overall

• Variance in thirds
• One third of genetic variance of academic
  performance is in common with general cognitive
  ability
• One third of genetic variance is general to
  academic performance, independent of general
  cognitive ability
• One third is specific to each domain
• Means learning abilities are not exactly the same
  thing genetically as general cognitive ability