[INTRO ♪].

How good is your memory? Like, try to remember this list of words: weather, snacks, cousin, cherry, floor, boats. [silently mouths words].

Okay, can you repeat that back to me? Whether you're generally good at memorizing things or not, if you're pregnant or recently had a baby, this task might be a little trickier. That's because many pregnant people experience a foggy memory that can last for years after the pregnancy ends.

This phenomenon has a number of names: “momnesia,” “mom brain,” “baby brain,” “pregnancy brain." And memory loss only scratches the surface of what's going on. Turns out, to prepare for a baby, pregnancy actually remodels the human brain. Pregnancy brain is best known for causing memory loss, but studies show that it can also involve sleepiness or fatigue, dips in attention, and slower processing speeds.

Pinning down the symptoms has been a challenge, partly because pregnancy can vary so much between people. For instance, those behavioral symptoms of pregnancy brain can start as early as the second trimester and last as long as two years after the baby's born. Or they can start as late as the third trimester and end just a few days after childbirth.

Or there might be no symptoms at all! These variations can make it hard to get consistent experimental results. But a 2012 study compared 19 years of research and found that pregnancy brain is a real, measurable phenomenon that affects memory in a very specific way.

With other kinds of memory loss, like amnesia, people have a complete inability to form new memories. But with pregnancy brain, it's harder to form certain types of memories. Specifically, memories that require effortful processing—like when you're actively trying to memorize information.

So this includes memory tasks like free recall, where you remember a list of items or words, one at a time. There's also delayed free recall, where you can remember information after some time or after a distraction. Like whether you can remember the list from the beginning of this video—I know I can't!

None of them. Boats? Was boat one of them?

And then there's prospective memory, where you remember to do something in the future— like deciding to make mashed potatoes for dinner, and then you remember to stop at the store on the way home from work. It's unclear why these specific types of memory are affected, but we have some ideas as to how memory loss can happen, because there are measurable changes in the brain. During pregnancy, brain changes are ultimately driven by sex hormones like estrogen, progesterone, and prolactin.

These hormone levels rise to super high concentrations during pregnancy, and fluctuate a lot during the third trimester. As this happens, the amount of some neurotransmitters also changes— including a decrease in serotonin and dopamine, and an increase in norepinephrine. That norepinephrine boost, which signals the fight-or-flight response, is also linked to an increased memory loss.

And all these chemical brain changes play a role in physical changes during pregnancy— although scientists aren't entirely sure how everything's connected. See, researchers have found that pregnancy causes significant changes in gray matter— the regions where most neurons connect and talk to each other. An increase in gray matter volume can mean that an area needs to make more connections, while a decrease can mean there's some fine-tuning going on, or a loss of information processing.

But basically, changes in volume generally mean a shift in how the brain handles information. A 2016 study published in Nature Neuroscience looked at the brains of 25 women who got pregnant for the first time, before and after they gave birth. And they compared this MRI data to some scans of the brains of their male partners, and the brains of women and men who didn't become new parents as controls.

The researchers found that, during pregnancy, the cortical midline, hippocampus, and areas of the prefrontal and temporal cortices had a significant loss of gray matter. And this decrease in volume had a correlation with memory loss. But it was also linked to an increase in sensitivity to emotional cues from the baby and emotional attachment.

Specifically, there was a correlation between gray matter loss and higher marks on the Maternal Postnatal Attachment Scale— a 19-point questionnaire used to measure how well a biological mother bonds with her child. They also did a follow-up MRI scan on 11 of those new mothers, and found that those brain changes can last at least two years after childbirth. And we're not sure how long it takes to get back to pre-pregnancy volumes of gray matter.

But overall, pregnancy brain seems to be an evolutionary thing that helps the baby survive— kind of like how morning sickness is annoying but it can offer protection from toxins. So meeting the demands of parenthood requires energy, time, patience, luck… and a little bit of brain remodeling. Thanks for watching this episode of SciShow Psych!

If you want to learn more about how new babies seriously affect your brain after they're born, check our our video about that very thing! [OUTRO ♪].