Pregnancy is a time of significant physical, emotional, and hormonal changes as your body grows a new human or sometimes humans and prepares to bring them into the world. While most expecting mothers may be aware of how pregnancy affects their bodies, many are surprised to learn about the dramatic impact it can have on their brains. Studies have found that pregnancy hormones such as estrogen, progesterone, and oxytocin play a critical role in rewiring the neural connections in the brain. These changes can result in enhanced communication between the brain’s regions, strengthening the mother-infant bond, and increasing maternal instincts. Although not every woman experiences the same effects, the fascinating findings about the ways in which pregnancy hormones shape our brains continue to shed new light on the all of the ways our bodies change during this incredible time.
The study, from the Francis Crick Institute, published in Science, shows that estrogen and progesterone activate a specific group of neurons in the brain, triggering parental behavior even before the arrival of offspring. These adaptations result in stronger and more selective responses to pups in mice.
Previous assumptions suggested that hormones released during childbirth were the major factor in initiating maternal behavior. However, the study also found that rodents who gave birth via Caesarean section and virgin mice exposed to pregnancy hormones still displayed maternal behavior, indicating that hormone changes during pregnancy may be crucial.
The research team discovered that female mice exhibited increased parental behavior during late pregnancy, even without exposure to pups. They identified galanin-expressing neurons in the medial preoptic area of the brain as being impacted by estrogen and progesterone. Estrogen reduced baseline activity while making the neurons more excitable, and progesterone rewired their inputs by recruiting more synapses.
When the hormones were made ineffective on these neurons, parental behavior did not occur during pregnancy or after giving birth. The study suggests that there is a critical period during pregnancy when hormones exert their influence.
While some of the brain changes lasted for at least a month after giving birth, others appeared to be permanent, indicating that pregnancy can result in long-term rewiring of the female brain.
Jonny Kohl, Group Leader of the State-Dependent Neural Processing Laboratory at the Crick, explained, “We know that the female body changes during pregnancy to prepare for bringing up young. One example is the production of milk, which starts long before giving birth. Our research shows that such preparations are taking place in the brain, too.”
The researchers believe that similar brain rewiring may occur during pregnancy in humans, as the same hormonal changes are expected to impact the same brain areas. This could influence parental behavior in combination with environmental and social factors.
Rachida Ammari, postdoctoral fellow at the Crick, added, “We’ve demonstrated that there’s a window of plasticity in the brain to prepare for future behavioral challenges. These neurons receive a large number of inputs from elsewhere in the brain, so now we’re hoping to understand where this new information comes from.”
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