Motherhood may actually cause the brain to grow, not turn it into mush, as some have claimed. Research published by the American Psychological Association found that the brains of new mothers bulked up in areas linked to motivation and behaviour, and that mothers who gushed the most about their babies showed the greatest growth in key parts of the mid-brain.

A group of researchers led by neuroscientist Pilyoung Kim, PhD, speculated that hormonal changes right after birth, including increases in estrogen, oxytocin and prolactin, may help make a mother’s brain susceptible to reshaping in response to the baby. The motivation to take care of a baby, and the traits of motherhood, might be less of an instinctive response and more of a result of active brain building, neuroscientists Craig Kinsley, PhD, and Elizabeth Meyer, PhD, wrote.

The researchers performed baseline and follow-up high resolution magnetic resonance imaging (MRI) on the brains of 19 women who gave birth at Yale-New Haven Hospital, of which ten gave birth to boys and the other nine to girls. A comparison of images taken two to four weeks and three to four months after the women gave birth showed that grey matter volume increased by a small but significant amount in various parts of the brain. In adults, grey matter volume doesn’t ordinarily change over a few months without significant learning, brain injury or illness, or major environmental change.

The areas affected support maternal motivation, reward and emotion processing, sensory integration, and reasoning and judgment. In particular, the mothers who most enthusiastically regarded their babies as special, beautiful, ideal, perfect and so on were significantly more likely to develop bigger mid-brains than the less awestruck mothers in key areas linked to maternal motivation, rewards and the regulation of emotions.

The mothers averaged just over 33-years in age and with eighteen years of schooling. All were breastfeeding, nearly half had other children and none had serious postpartum depression. Although these early findings require replication with a larger and more representative sample, they raise intriguing questions about the interaction between mother and child (or parent and child, since fathers are also the focus of study). The intense sensory-tactile stimulation of a baby may trigger the adult brain to grow in key areas, allowing mothers, in this case, to “orchestrate a new and increased repertoire of complex interactive behaviours with infants,” the authors wrote. Expansion in the brain’s “motivation” area in particular could lead to more nurturing, which would help babies survive and thrive physically, emotionally and cognitively.

Further study using adoptive mothers could help “tease out effects of postpartum hormones versus mother-infant interactions,” said Kim, and help resolve the question of whether the brain changes behaviour or behaviour changes the brain – or both. The authors said that postpartum depression may involve reductions in the same brain areas that grew in mothers who were not depressed.

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