New research conducted in mice suggests that pregnancy results in a permanent rewiring of neurons, shedding light on the profound influence of hormones on behavior. This groundbreaking study offers insights into the biological basis of parenting instincts and may have implications for understanding postpartum mental health.
The study, led by Dr. Jonny Kohl at London’s Francis Crick Institute, indicates that significant changes in the brain occur late in pregnancy in response to the hormones estrogen and progesterone, triggering parenting instincts. Scientists believe that similar changes likely occur in the human brain, potentially opening avenues for a deeper understanding of parenting behavior and postpartum mental well-being.
Dr. Kohl explains, “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.”
This discovery aligns with previous brain imaging research in women, which has demonstrated enduring changes in brain volume and activity long after pregnancy. However, Kohl acknowledges that human parenting is far more complex than in mice. “We have NCT classes, observational learning, all these environmental influences,” he noted. “We don’t have to rely on those hormonal changes to such a degree.”
The research was conducted using mice as subjects, creatures that undergo a dramatic behavioral shift. Virgin female mice typically show no interest in pups, while mouse mothers dedicate most of their time to caring for their young. Previously, it was believed that this behavioral transformation occurred during or after birth, possibly triggered by hormones like oxytocin. However, the new findings suggest that this change happens earlier in pregnancy and may have lasting effects.
In the study, miniature devices were attached to the mice’s heads to record neuronal activity in the hypothalamus, a region previously linked to parenting behavior. The results revealed that estrogen reduced the baseline activity of these neurons while making them more responsive to incoming signals. Progesterone, on the other hand, rewired the neural connections, resulting in denser connectivity with other parts of the brain. These changes appear to be permanent.
Dr. Kohl explained the significance, stating, “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 behavior 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.”
When the researchers engineered mice so that the neurons were insensitive to hormones, they failed to transition to parental behavior even after giving birth, underscoring the critical role of hormones during late pregnancy.
While hormonal changes are just one factor influencing parenting behavior in humans, understanding these brain changes may provide valuable insights into parental bonding and conditions such as postpartum depression and psychosis.
Prof. Robert Froemke of NYU Langone, who was not part of the study, commented, “There is still so much we don’t understand about parenting and hormone signaling in the body and brain – these results are a solid step in that direction. Parenting is among the most complex and difficult set of behaviors we and other animals engage in, and there’s not a lot of room for ‘trial and error,’ especially in the earliest days postpartum when infants need a lot of care. The hormonal changes documented here seem to help prime the parental brain to respond to infant needs right out of the gate, so that parental rodents, much like new human parents, can do a good job and be sensitive to their babies as soon as possible.”
