Ha! This is fascinating:
A paper titled, “Maternal Defense: Breast Feeding Increases Aggression by Reducing Stress” which appears in the September issue of Psychological Science, suggests that mothers who nurse are actually primed to more aggressive than women who are not not nursing.
One of the many cool things about this study, which involved making nursing moms play violent video games with name-calling assholes, is that the aggression is not experienced as stress. In fact, the nursing mothers have lowered blood pressure during their aggressive behavior. What appears to be happening is that lactating hormones make moms both more aggressive and more calm. Kind of a Cool Hand Luke situation.
Non-human mammal studies have shown a similar kind of behavior in lactating animals– they are more aggressive due to a hormonally-triggered reduced fear response. I recall taking pictures of some baby calves once and the mother cows– separated by a fence– went ballistic with a terrible, hostile wailing sound. I was a new mother at the time and that sound broke my heart. Maternal instincts are fierce! Researchers wondered if lactating humans showed a similar kind of vigilance and hostility to aggression/threats.
So they had three groups of women–nursing moms, formula-feeding moms and non-moms–play video games with an opponent instructed to be overtly confrontational. When a study participant won a round she had the option of sending a “punitive sound burst” to her opponent. The nursing moms shot off twice as many of these sound bursts (curses, basically) as the non-nursing moms and the non-moms.
Check it out: “Breast-feeding mothers inflicted louder and longer punitive sound bursts on unduly aggressive confederates than did formula-feeding mothers or women who had never been pregnant…. Exclusively breast-feeding mothers had lower [blood pressure] during the aggressive encounters relative to the other groups, and [blood pressure] correlated inversely with aggressive behavior. Together, these findings suggest that in humans, as in many other mammalian species, lactating mothers are more likely to aggress against hostile conspecifics than are non-lactating mothers or [women who have never given birth], at least in part because they experience dampened arousal in response to stressful aggressive encounters.”
This all fits in quite nicely with everything I’ve read about “Mommy Brain.” At the end of pregnancy there are already changes to the way women think. They may become spaced out about some things– the brain of a very pregnant woman/new mother is temporarily smaller than at other times. But in a number of studies, often involving lactating non-human mammals such as rats, there’s increased resourcefulness, vigilance and *bravery,* especially vis-a-vis protecting their offspring.
I doubt a nursing mother would get riled up over any old thing, but if seriously provoked … she may lash out with a cool confidence. Kind of throws a new and powerful spin on the notion of nurturing behavior.