Brain development How genes and experience make … · More on environmental influences “I want...
Transcript of Brain development How genes and experience make … · More on environmental influences “I want...
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Brain development: How genes and
experience make us who we are
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Plan • Genes and environment
– and their interaction
• Plasticity (ie effects of environment) – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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Plan • Genes and environment
– and their interaction
• Plasticity (ie effects of environment) – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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Experience
Behavior
Genes
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Genes and environment: the “nature versus nurture” debate
"Give me a dozen healthy infants & my own specific world to bring them up in, & I'll guarantee to take any one at random & train him to become any type of specialist I might select - doctor, lawyer, artist, merchant, chef & yes, even beggar & thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors."
- John B. Watson, 1924
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Genes and environment: the “nature versus nurture” debate
”Compensatory education has been tried and it apparently has failed."
- Jensen, 1969 “The story of attempts to raise intelligence [by
environmental enrichment] is one of high hopes, flamboyant claims, and disappointing results."
- Hernstein & Murray, 1994
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Behavioral genetics • Partitions variance in a trait (eg IQ) into
genetic variance and environmental variance
• Surprising range of traits show substantial heritability (IQ, vulnerability to most mental illnesses, personality, political orientation)
• Clever (but imperfect) methods – Adoption studies – Twin studies
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Twin studies
• Workhorse of behavioral genetics
• Measure correlations of a trait between twins
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Twin studies
• Workhorse of behavioral genetics
• Measure correlations of a trait between twins
A 105 130 110 145 85 …
B 100 140 105 140 91 …
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Twin studies
• Workhorse of behavioral genetics
• Measure correlations of a trait between twins
• eg, at right, fairly high correlation in IQ
A 105 130 110 145 85 …
B 100 140 105 140 91 …
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Twin studies
• The correlation depends on the kind of twins – identical or fraternal – Identical, monozygotic, share all genes – Fraternal, dizygotic, share 50% of genes
• If a trait is strongly genetic, eg eye color, then…
• If a trait is not genetic, eg language spoken, then…
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Cortical thickness Schmidtt, Cerebral Cortex, 2008
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Heritability estimates are not absolute – they describe variances in a particular population
Turkheimer (Psych Sci, 2003) twin study of intelligence, showing heritability as a function of socioeconomic status
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Plan • Genes and environment
– and their interaction
• Plasticity – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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Gene-environment interaction Caspi, Science, 2002
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Gene-environment interaction Caspi, Science, 2003
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Plan • Genes and environment
– and their interaction
• Plasticity – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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More on environmental influences:
“I want to say one word to you, just one word: Plastics Plasticity”
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Plasticity
• Neuronal connections depend on neuronal activity
“Neurons that fire together wire together” • Small amount of neurogenesis as well • Can actually change macroscopic size and
shape of brain!
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Plasticity
• Changes in brain as a result of experience
Maguire, PNAS, 2000
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Plasticity
• Changes in brain as a result of experience
Draganski, Nature, 2004
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Plan • Genes and environment
– and their interaction
• Plasticity – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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Limits on plasticity
• “Critical periods,” “sensitive periods”
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Critical periods
• Vision
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Critical periods
• Language – Studies of second language acquisition
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Critical periods
• Language – Studies of second language acquisition – First language acquisition
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Plan • Genes and environment
– and their interaction
• Plasticity – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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Building a brain
• Much known about prenatal and postnatal events at the cellular level
• Generally hard to relate this level to psychological phenomena
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Prenatal processes
• Cell birth • Cell migration • Cell differentiation • Cell maturation • Synaptogenesis • Cell death and
synaptic pruning • Myelination
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Postnatal development • Synaptogenesis
continues
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Postnatal development
• Myelination continues – Enhances neuronal
conduction velocity – Continues through
young adulthood
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Postnatal development • Pruning continues
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Plan • Genes and environment
– and their interaction
• Plasticity – and its limits (ie critical periods)
• Lifespan brain development – Mechanisms – Regional differences
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Adolescent brain development
Allstate Insurance advertisement
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Adolescent brain development
• Two systems maturing at different rates
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Key Points • Genes and environment
– Both important – interact
• Plasticity – Ubiquitous, evident even at macroscopic scale – but has its limits, some severe
• Lifespan brain development – Cellular mechanisms and regional differences
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Questions, comments?