Pregnancy Causes Changes in Brain Structure

Intriguing research describing changes in the brain linked to pregnancy has recently been reported by Elseline Hoekzema and colleagues in the journal Nature Neuroscience. Using MRI (magnetic resonance imaging), this research team examined structural changes in the brain that occur in women during their first pregnancy. The investigators compared brain structure before pregnancy, shortly after pregnancy, and two years later. They compared changes observed in the women who became pregnant to changes in a matched group of women who did not become pregnant as well as to changes in the fathers. In addition, they studied whether the amount of structural change correlated with maternal behaviors.

The investigators found that specific regions of the mother’s cortex decreased in size during pregnancy. These structural changes did not occur in women who did not become pregnant or in the fathers. The changes were so consistent that a computer could determine with 100% accuracy which brains were from the women who had become pregnant and which were from the never-pregnant women.

Interestingly, the regions of the cerebral cortex that changed in volume are known to be involved in social cognition and overlap significantly with cortical regions involved in the brain network thought to underlie “theory of mind” processing. Theory of mind relates to the ability to understand the mental states of others and to recognize that others may experience mental states different from one’s own. These brain regions may be involved in the mothers’ ability to be sensitive to their newborns’ needs.

Hoekzema and colleagues showed that the more the volume in these regions decreased, the more the mothers were responsive to their babies. The exact nature of the structural changes associated with the diminished volume observed in these brain regions is not known; i.e., it is yet to be determined whether the changes in volume involve changes in numbers of neurons, glia, and synapses and/or changes in other characteristics of neuronal and glial cells.

Somewhat surprisingly, these pregnancy-linked brain changes do not appear to reverse quickly. When the investigators examined the brains of the mothers two years later, most of the pregnancy-related changes were still present. One region that returned to pre-pregnancy volume was the hippocampus, a brain region that is involved in many aspects of learning and memory.

This carefully done study represents an important demonstration of the structural plasticity of the human brain. Our brains are engineered to adapt to various circumstances. One essential role of any species is to reproduce and maximize the chances of survival of its young. Changes in the brains of mothers that enhance their ability to recognize the needs of their babies make perfect sense. It will be interesting to see whether these results can be replicated in other cohorts of mothers and to determine how long the changes persist and whether similar or other changes accompany subsequent pregnancies.

This column was written by Eugene Rubin MD, PhD and Charles Zorumski, MD