The human brain goes through significant changes during pregnancy with few regions untouched, according to the first ever map of this over the course of gestation and beyond.
Some regions of the brain shrink during this time, while others grow and become better connected. These changes are thought to enable mothers to develop strong bonds with their baby and adapt to the demanding task of caring for them. A better understanding of this remodelling could explain several pregnancy-related behaviours and help people at risk of mental health conditions, such as postnatal depression.
鈥淭he maternal brain undergoes a choreographed change across gestation, and we are finally able to see it unfold,鈥� says at the University of California, Santa Barbara, whose team carried out the work.
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Previous studies have taken , but what has remained a mystery is exactly how it alters over this time and beyond. To find out, Jacobs and her colleagues scanned the brain of a 38-year-old, first-time mother 26 times, starting from three weeks prior to conception through to two years after giving birth.
The most pronounced changes occurred in the brain鈥檚 grey matter 鈥� the wrinkly outer layer that is packed with neuron cell bodies and synapses, the junctions between the cells. The woman鈥檚 grey matter volume decreased, but its connections multiplied.
This major remodelling, sometimes called neuroplasticity, occurred in grey matter across the brain, at three times the rate seen in eight non-pregnant women who also had their brains scanned over the same time.
鈥淪ometimes people bristle when they聽hear that grey matter volume聽decreases聽across pregnancy, but this isn鈥檛 necessarily a bad thing,鈥� says Jacobs. Think of the brain a bit like Michelangelo鈥檚 David: a big block of marble had to be chipped away to create the beautiful sculpture, she says. A similar thing happens in the brain, with the changes probably reflecting a fine-tuning of brain circuits, like during puberty as the brain becomes more specialised.
Jacob鈥檚 study also found prominent increases in white matter, the nerve fibres that connect neurons and help different brain regions communicate. These increases peaked in the second trimester of the pregnancy, then returned to pre-conception levels after the baby was born. The changes were particularly noticeable in regions associated with sensory attention, emotion, self-directed thought and introspection.
鈥淎ll in all, this supports the reconceptualization of motherhood as one of the periods of highest neuroplasticity in adult life,鈥� says at Gregorio Mara帽贸n Hospital in Madrid, Spain.
This remodelling of the brain during pregnancy probably enables the onset of certain maternal behaviours. For instance, in rodents, increases in steroid hormones during pregnancy trigger brain changes that .
Studies suggest something similar may be happening in people. For instance, in 2017, researchers showed that the magnitude of change in grey matter volume corresponds with degree of parental attachment. But there is also a that shows how brain changes during pregnancy confer a vulnerability to mental health conditions.
The new study adds to our understanding of the broad range of changes that the brain goes through during and after pregnancy, but doesn鈥檛 tell us exactly how they are linked to behaviours, says Jacobs. It isn鈥檛 clear, for instance, why white matter changes revert back to pre-pregnancy levels while some grey matter changes persist for at least two years.
It may be that the permanent changes are associated with behaviours important to the survival of the child, such as eliciting maternal behaviour. Other research supports this idea. In adolescence, for example, we see .
But Jacobs points out that parents who use surrogates, adoptive parents and fathers still display the nurturing behaviours needed to care for their child.
We probably need a few more years of research before we understand the impact of these brain changes, says at Amsterdam University Medical Centre in the Netherlands, whose work has shown they are .
The next step may be to analyse how the timing of brain changes differs among individuals, says Ca帽abate. This might help explain why some people struggle to bond with their babies, she says.
But we are still quite far from being able to make specific recommendations, says Ca帽abate. 鈥淔irst, we need to determine whether the brain changes apply consistently across subjects and if they relate to variables such as maternal bonding or mental health.鈥� We can only test potential interventions when we understand the causal factors, how they link to pregnancy hormones and the subsequent consequences.
Nature Neuroscience
