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The Truth About “Mommy Brain”

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The term “mommy brain” just took on new meaning. When researchers scanned the brains of new moms in a recent study, they found that key areas of the brain involved in reasoning, judgment, emotion and sensory integration actually grew in volume in the months after childbirth.

The study, published in the journal Behavioral Neuroscience last month, wasn’t the first time scientists had shown that motherhood gives us a mental boost. In fact, decades of studies on animals and humans have revealed that our neurons reorganize when we have a child, making us more intuitive and wiring us to find our babies – and all the diapering, soothing, and feeding they require – highly rewarding.

At the brain’s emotional core, new moms are more empathetic creatures. As someone who used to reserve tears for a major crisis and now can barely watch an HGTV show without waterworks, I can’t say this comes as any surprise to me. What’s interesting are the causes of all this empathy.

What Makes Moms’ Brains More Empathetic

  • We usually think of the changes in new moms’ brains as being biologically pre-determined – as if the hormones of pregnancy and new motherhood fine-tune our nurturing skills – but the current thinking says it actually goes the other way around. It’s the act of parenting that wakes up key parts of our brains. And that has big implications for everything from adoption to postpartum depression.
  • Cindy Hazan, a Cornell University researcher (her former graduate student is an author on the brain scan study), says that a mother’s nervous system is oriented towards attachment and bonding. When researchers scan the brains of new mothers while they look at pictures of babies, for example, they see that empathy circuits are on high alert. Parts of the prefrontal cortex, hypothalamus and structures in the limbic system (the brain’s emotion center) light up in response to infant sights and sounds. When a mom is shown a picture of her own baby, these regions become even more active.That means we’re wired not just to detect, but also feel our baby’s cues – we don’t simply read signs of distress or joy, they actually resonate in our own emotional circuits. It’s nature’s way of making sure we’re driven to respond.
  • These emotion and empathy areas are also highly intertwined with reward regions, like the brain’s dopamine-driven substantia nigra. In rats, making lesions to these parts of the brain, or cutting off communication to those critical parts of the prefrontal cortex, essentially turns off the animals’ caretaking instinct, making it uninterested in picking up or licking its pups. It even makes infanticide more likely.

  • The intact (human) mom’s brain, on the other hand, gets a shot of uplifting chemicals from all of the holding, feeding, cooing and so forth – feeding into a reward-driven loop. The more chemicals we receive, the more we want, so the more eager we are to interact with our infants. We are, for all intents and purposes, addicted to parenting. Some researchers think this circuitry might hold a key to treating postpartum depression – it could be that some moms with PPD have an interruption in these pathways and don’t get the same neurochemical boost.
  • Hazan points out that the recent study and others like it seem to indicate that our biology doesn’t just change after birth (the experience to four months later) – but they found that the changes in brain volume didn’t take place until the second scan. That suggests that all the contact and nurturing of the early months works into a feedback cycle: We’re driven to respond, and doing so builds our parenting brain muscle that much more.

As I pointed out recently, though, moms don’t have an exclusive claim on the biological changes of parenthood – dads’ chemistry and brain structure has been shown to change as well.

How Fatherhood Changes Dads

  • When scientists look at the brains of these primates, they find that after mom gives birth, dad actually grows more neuron connections in certain areas of the brain’s prefrontal cortex – regions involved in caretaking and bonding.
  • After childbirth, human dads have a drop in cortisol and testosterone (which scientists think makes them less likely to fight and more likely to devote energy to caretaking).

That parenthood changes dads, too, makes sense in light of the new study: If the parent-brain is shaped by the act of caretaking itself, then anyone is fair game. Biological mom or dad, any combination of same sex partners, adoptive parents and so on – a person who loves, holds, nurtures and forms a primary bond with a baby is re-wired at the core.

I have a feeling evolution is responsible for this. Throughout human history, babies have had to be flexible enough to be born into an endless number of environments and family circumstances. They learn patterns quickly and over time figure out who to attach to and who to trust. And their finely-tuned baby signals – the smiles, babble, reaching and touching – send a direct message to our parent-primed brains that we should keep them close and safe.

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