Pregnancy brain: How neurons get rewired to prepare for motherhood

Researchers at the Francis Crick Institute have discovered that the brain undergoes significant rewiring during pregnancy, preparing females for motherhood. 

According to the study, pregnancy hormones such as oestrogen and progesterone are instrumental in initiating these brain changes.

Parental behaviors

The researchers found that these hormones act upon a select group of neurons in the brain, inducing parental behaviors even before the offspring are born. 

In mice, the activated neurons led to heightened and selective responses towards pups, which is a crucial aspect of maternal care.

Hormonal changes

Traditionally, it was believed that the onset of maternal behaviors was primarily triggered by hormones released during childbirth. 

However, earlier studies indicated that even rats who underwent Caesarean sections and virgin mice exposed to pregnancy hormones exhibited maternal behaviors. 

This observation implied that hormonal changes occurring during pregnancy play a pivotal role in promoting maternal instincts.

The researchers observed enhanced parental behaviors in female mice during late pregnancy. Interestingly, exposure to pups was not a prerequisite for the development of these behaviors. 

Galanin-expressing neurons

The study highlighted the role of galanin-expressing neurons situated in the medial preoptic area (MPOA) of the hypothalamus, a region associated with parenting. These neurons were particularly influenced by oestrogen and progesterone.

Oestrogen was found to decrease the baseline activity of these neurons while increasing their excitability. 

Progesterone, on the other hand, altered the neurons’ inputs by increasing the number of synapses, which are crucial communication points between neurons. 

When these neurons were made insensitive to hormones, mice failed to exhibit parental behaviors, highlighting the significance of hormonal influence during pregnancy.

Long-term brain rewiring 

The researchers noted that some of these neuronal changes persisted for at least a month post-childbirth, with others potentially being permanent, indicating long-term brain rewiring as a result of pregnancy.

“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,” explained study co-author Jonny Kohl. 

“We think that these changes, often referred to as ‘baby brain,’ cause a change in priority – virgin mice focus on mating, so don’t need to respond to other females’ pups, whereas mothers need to perform robust parental behaviour to ensure pup survival.” 

“What’s fascinating is that this switch doesn’t happen at birth – the brain is preparing much earlier for this big life change.”

Window of brain plasticity 

“We’ve demonstrated that there’s a window of plasticity in the brain to prepare for future behavioral challenges,” said co-first author Rachida Ammari. 

“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.”

Study implications 

The team is optimistic that their findings may have implications for understanding pregnancy and motherhood in humans, as similar hormonal changes are expected to influence the same brain regions. 

The experts believe that these alterations in brain wiring could work in tandem with environmental and social cues to influence parental behaviors. 

With these insights, the study sheds light on the complex interplay between hormonal changes during pregnancy and the onset of maternal instincts and behaviors.

The study is published in the journal Science.

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