Chapter 2: Epigenetics of mammalian parenting

1. 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.

2. 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.

3. 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.

4. 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.

5. Epigeneticsand 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.

6. 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.

7. 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 r-strategy) • Lo stress: mature slowly, reproduce later, high parental investment (more K-strategy)

8. 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.