The Science of Mother's Day

Some sad orphans
Some surprising rats
Those orphans again
Day care blues
Mice and men


A child views a series of faces expressing emotions as part of a study that indicates that child abuse can affect brain development.

Photo courtesy of the UW-Madison Office of News and Public Affairs.


Healthy for rats = healthy for people?
In the mid-1950s, psychologist Seymour Levine wanted to study the effects of early trauma on animal behavior. Figuring the ultimate trauma for a baby rat was removal from its mother, he separated some pups for two or three minutes each day during the first weeks of life.

Oddly enough, when he tracked the pup's health, the brief separation proved helpful. The pups grew up larger and "less fearful, with less of a stress response," says Levine, who's now at the University of Delaware. As they aged, the separated rats' memories declined more slowly than those of control animals.

Levine was puzzled to see such a big effect from what he calls "such a small change." After all, the separated pups had no more overall physical contact with mom than other pups. However, he did notice the mothers diligently licking and grooming the pups after their reunion, and eventually attributed their better health to this extra care. Brushing the pup's anal-genital region for 45 minutes a day, for example, produced the same benefits.

Next question
Cynics might argue that he just proved that a rat mom could be replaced by a paintbrush, but how, exactly, did mom's care and affection affect the pup? The answer was eventually traced to the regulation of a neurological-hormonal system that prepares animals for stress.

The interactions between the brain and hormones are way too complicated for us Why Filers to understand, let alone explain, so we'll be brief -- promise! The response begins when the brain detects danger and directs a gland called the hypothalamus to release corticotropin-releasing hormone (CRH). CRH stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH), which causes the adrenal gland to release cortisol, the "stress" hormone.

This so-called HPA axis (that stands for hypothalamus-pituitary-adrenal) often works in tandem with the faster, more familiar release of adrenaline into the bloodstream. Adrenaline increases the heart rate and blood pressure, readying the body for immediate "fight or flight."

Phew! Having summarized a semester's worth of stress physiology in five sentences, let's hustle on...

Cortisol, the stress hormone made by the HPA axis, is handy stuff. When it attaches to cell receptors, the cells make fat and protein available as energy sources. Overall, the HPA axis diverts the body from long-term needs like growth, reproduction and fighting infection to defending against more immediate threats. The stress response also forces the brain to concentrate on the threat and ignore irrelevant stimuli.

If we're fleeing a predator or fighting a war, cortisol and adrenaline are just what the doctor ordered.

Excessively excessive
But too much of a good thing is not good. Normally, cortisol levels fall about 45 minutes after a threat dissipates. That's just as well, since there's strong evidence that sustained high levels of cortisol in people can impair thinking, damage the heart, increase susceptibility to infection, and cause early death.

The ability to measure cortisol elevated "stress" from a vague concept into a measurable molecule with vast consequences for health, happiness and the way we raise our children.

Just as mother's attention reduced the stress response in rats, trauma early in life can permanently jack it up. Although this predisposes the animal to stress-related disease later in life, it does have survival value, says Michael Meaney, a psychiatrist at McGill University in Montreal, Canada, since animals that detect stress early are able to overcome stress later in life.

But mis-regulation of the HPA axis is associated with grave problems like heart disease and depression. "Depressed patients as a group have quite high activation of HPA," says Charles Nemeroff, chair of the Emory Medical School and a long-time researcher into the biology of stress and depression. Speaking at the Fifth Annual Wisconsin Symposium on Emotions, Nemeroff added that "There are plastic periods, when events -- negative or maybe positive -- occur with long-lasting consequences for the susceptibility to psychiatric disorders."

Since brain researchers use "plastic" to describe the ability of the brain to rewire itself to meet new demands and acquire new skills, you could translate that into: early injuries can cause lifelong psychological damage.

The research raised a key question: can we change our mothering -- and fathering -- practices to lower the stress response and improve health? If small changes -- short separations and brief bouts of licking -- can affect a rat's health, it may not require the level of neglect found in Romanian orphanages to stunt physical and emotional growth.

For example, new research by pyschologist Seth Pollak of the University of Wisconsin-Madison shows that abused children react more strongly to the sight of an angry face than other children. Angry faces, but not happy or fearful ones, triggered a strong electrical reaction in the brains of the abused children. computer faces

Detecting anger is a survival skill for abused children, yet their concentration on anger may cause them to perceive anger when it does not exist, Pollak said. By constantly being on the lookout for anger, they could wind up in more fights and confrontations.

One of many who followed up on Levine's separation experiments was Michael Meaney, a psychiatrist at McGill University in Montreal, Canada. Meaney agrees that the effects of good or bad maternal care can affect an animal's stress response over a lifetime.

In 1998, Meaney's research group reported that rat pups that got more licking and grooming had higher concentrations of benzodiazepine (natural valium) receptors in parts of the brain that affect fearfulness. More receptors would increase the brain's response to this calming chemical. The research team wrote that the results "suggest that maternal care during infancy serves to 'program' behavioral responses to stress by altering the development of neural systems that [carry out] fearfulness" (see "Maternal Care..." in the bibliography).

In other words, mom's soothing behavior leads to less stressed children -- among rats, at any rate.

Astonishingly, Meaney also found evidence for non-genetic inheritance of behavior. When a daughter rat who received relatively little maternal care becomes a mother, she likewise does less licking and grooming of her pups. This may sound like genes at work, but it's not: Daughters shifted to foster mothers reflect the behavior of the foster mother, not the birth mother.

What happens if the HPA stress response is permanently turned on? Meaney says "When you look at individuals who live under constant levels of stress, there's a permanent activation of the cardiovascular system" and high levels of fat and sugar in the blood. Among other problems, high cortisol levels interfere with the action of insulin, the hormone that regulates sugar levels, perhaps explaining why adult-onset diabetes is more common among people who recall having had a poor relationship with their parents.

In rats, an enriched environment after weaning can help reverse the effects of heightened stress.

High cortisol levels occur in rats separated for long periods from their mothers, and in some soldiers, stressed-out refugees, mothers and children in inner-city ghettoes, and those Romanian orphans.

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