Download Chapter 2: Epigenetics of mammalian parenting

Chapter 2: Epigenetics of mammalian parenting
Recent studies have parenting have
indicating that early caregiver-infant
interactions can have lasting effects on
development.
Just as early experiences shape visual and
auditory parts of the brain, early tactile
experiences appear to have important
effects on neuroendocrine function with
important effects on stress response, social
development and reproduction.
Many of these lasting effects may be
mediated by epigenetic changes.
Epigenetics: factors that can alter the
activity of genes or gene expression without
altering the DNA sequence.
Epigenetics and mammalian parenting
• Studies in the mid-1980’s showed
that tactile stimulation of premature
infants could promote weight gain,
attention, alertness, and behavioral
maturation.
• Later studies looked at Kangaroo
care – constant or frequent skin to
skin contact between mother and
infant (believed to be part of EDN).
• KC for infant: improved temperature
regulation and enhanced growth
• KC for mother: increased positive
affect, sensitivity to infant cues,
better breastfeeding, reduced
incidence of maternal rejection of
infant.
Early touch
• Increased infant contact also associated with higher oxytocin levels in
both mothers and fathers. Oxytocin thought to play a role in social
bonding.
• Opposite patterns also observed. Lack of early infant-maternal contact
associated with negative outcomes: growth retardation, heightened stress
response, impaired social attachments.
• Brain changes found in adolescents who as infants were institutionalized:
reductions in grey and white matter; enlarged amygdale. (Neocortex
sacrificed for flight-fight response).
• Similar findings in animal studies – most famous Harlow studies with
rhesus macaques.
Rats: Maternal licking/grooming (L/G)
• In rats: lack of maternal licking associated with impaired physical and
social development.
• Even without experimental intervention, lab rat mothers vary in L/G
(licking/grooming). Lower levels of L/G in infancy associated with (in
adulthood):
• Heighten glucocorticoid levels (stress response hormone)
• Decreased exploratory behavior in novel environments
• Increase fear reactivity
• Decrease hippocampal plasticity – reduced learning and memory capacity
• All these effects are traceable to changes in neurotransmitter receptor
and activity levels in the brain.
Epigenetics and the lasting effects of maternal touch
• How can gene regulation affect
development?
• Activity of genes is either
suppressed (made less
accessible) or enhanced.
• DNA methylation: methyl groups
are added directly to DNA
(cytosine neucleotides) which
inhibit accessibility, thus reducing
gene expression.
• Histone modification: directed at
histone proteins around DNA, not
directly targeted at DNA. Can
have either activating or
repressing effects on gene
expression.
Epigenetic Effects
• Low maternal L/G in rats appears to be associated with methylation and
histone modifications leading to gene suppression
• Similar effects found in humans: higher levels of DNA methylation found
in blood samples of institution raised children.
• Evidence for multigenerational continuity in maternal care practices.
Individuals with secure attachment to their parents (presumably fostered
by high maternal tactile stimulation) have children and grandchildren who
are securely attached to their parents.
• Is this transmitted epigentically as well as behaviorally?
• In both rats and humans evidence of increased DNA methylation found in
abused offspring.
Is low maternal stimulation always maladaptive? Maybe not.
• Low L/G offspring found to be
more sexually receptive and to
have greater hippocampal
plasticity under stressful
conditions.
• Consistent with Belskey’s
theory that variation in
maternal behavior in humans
may be adaptive response to
varying levels of stress in
rearing environment:
• High stress: mature quickly,
reproduce early, limited
parental investment (more rstrategy)
• Lo stress: mature slowly,
reproduce later, high parental
investment (more K-strategy)
Final Thoughts
• Sensitive periods are general phenomena in
developments. Long history of this in sensory and
language development. Touch chapter points to sensitive
period for social/emotional development.
• That somatosenory input should be critical to biology
behind social/emotional development should not be
surprising. It is an evolutionarily old and highly
conserved system. The skin is our largest sense organ.
• The role of epigenetics emphasizes the nature-nurture
interaction of development. There is no either/or.