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Stressful early environments affect the brain in ways that are inherited. Majority of abusive parents were abused themselves as children. Now we are starting to understand the underlying psychological and biological mechanisms thanks to animal experiments. This research is of some practical importance given that abusive parenting is associated with low IQ, poor academic performance, low earning capacity, psychopathology, drug addictions, obesity, and overall health problems.
The Vicious Cycle of Abusive Parenting
The cycle of violence in families has parallels in the intergenerational transmission of maternal behaviour in other species, particularly rats and monkeys.
Good evidence is displayed on cross-generational pattern of “abusive” parents being children of abusers is partly explainable in terms of epigenetic effects of childhood experience that are transmissible through the germ line. Experiments with rats based upon the phenomenon of some rat mothers being more attentive to their offspring than others are. Maternal care in rats influences the attentiveness of females to their own offspring when they become mothers themselves.
Animal Experiments
Maternal licking affects the pattern of DNA methylation in rat pups' brains so that there is greater expression of glucocorticoid receptors for pups that are licked more (2). Behaviorally, greater expression of glucocorticoid receptors is associated with greater capacity to deal with stressful situations while remaining calm. This means that rats receiving a lot of maternal licking are less fearful in novel situations.
As for humans, childhood abuse is linked with abnormal methylation in the adult brain according to analyses of suicide victims. Specifically, there was greater methylation of the glucocorticoid promoter in the brains of suicides who had experienced childhood abuse compared to those who had not. As a result they had decreased glucocorticoid receptor expression.
Research on rhesus monkeys also suggests that abusive early experiences may alter the brain in similar ways to those recorded for rats and humans.
Just as some rats make more nurturant mothers than others, some rhesus monkeys handle their infants roughly and there is a similar cross-generational pattern as observed for humans. Cross-fostering experiments found that intergenerational transmission of infant abuse in rhesus monkeys is the result of early experience rather than genetic inheritance. This is likely due to a combination of social learning and altered DNA methylation.
In rat experiments, pups who received less licking from mothers had increased methylation of the BDNF gene in the frontal cortex. In humans, that methylation pattern is associated with major psychoses including schizophrenia and bipolar disorder.
So lukewarm maternal care can have substantial effects on the developing brain that makes individuals more vulnerable to stressors later in life. One implication is that there would be reduced impulse control, and therefore greater likelihood of committing serious crimes, including crimes of violence.
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Category(s):Abuse / Abuse Survivor Issues, Physical Abuse
Source material from Psychology Today
