As unique and diverse as all human beings across the globe may be, they all came to the world in the exact same way: a gradual progression from zygote to fetus to infant. And all of us grew in the womb of a female host — our mothers. The first and most primal of relationships is not only experienced by every human being, but has the capacity to change every human being, socially, psychologically, and, perhaps most surprisingly, on a cerebral level.
These changes begin immediately in the mother’s brain following birth. A study published in Behavioral Neuroscience concluded that the size of mothers’ brains increased shortly after childbirth. The more excitement and joy a mother expresses correlates with how much her brain grows throughout the first few months of motherhood. Increases in gray matter have been documented in the hypothalamus, amygdala, parietal lobe, and prefrontal cortex, regions responsible for emotion, reasoning, and judgment, the senses, and reward behavior. Researchers measured the enthusiasm of the mother based on the choice of words they used when interviewed. Those who used words like “special,” “beautiful,” “ideal,” and “perfect,” were more likely to increase the size of their midbrain following childbirth.
So what brings about these changes? Dr. Pilyoung Kim, principal investigator at the Family and Child Neuroscience Laboratory at the University of Denver, proposes that hormonal changes affecting the brain — caused by increases of levels of estrogen, oxytocin, and prolactin — happen immediately after birth. The enthusiasm of these new moms also stems from the brain’s pleasure-reward systems (particularly the substantia nigra). A sort of positive feedback loop seems to be operating: a baby’s smile can release dopamine in a mom’s pleasure-reward centers, further reinforcing maternal behavior, and quite possibly increasing maternal brain growth. Perhaps after all there’s some truth to the idiom that mothers know best.
The rewards of this interaction go beyond the mother and her infant. According to Dr. Stuart Basten, a researcher at the University of Oxford, “If parenthood is a pleasurable — or at least tolerable — experience, the chances of deciding to produce a second or third child are surely greater. It also underwrites the chances of survival of the child.” The pleasure of being a new mother indirectly influences the perpetuation of the human species as a whole.
In addition to growth of gray matter, there are other measurable changes in the brain activity of new moms. For instance, a study published in Frontiers in Psychology demonstrates that mothers who watched silent videos of their own child experienced more brain activation than those who watched videos of other babies. Brains also showed increased activity in mothers when their infant was crying as opposed to smiling. Scans of their brains suggest that particular circuits in the brain are activated when a mother distinguishes the smiles and cries of her own baby from those of other infants. These regions are the amygdala and the insula — areas associated with emotional responses and theory of mind functions.
Because of these changes in brain activity and size, a new mother develops novel abilities to protect her baby from harm. Dr. Adam Franssen, a biology professor who conducts animal studies, recognizes that not only are mothers able to maintain their calm in stressful circumstances that would leave the rest of the room in a panic, but are also more aggressive at defending their offspring. If there is an intruder, moms will fight against it more ferociously than nonmothers. Part of detecting these threats seems to be emotional intelligence, the ability to recognize hostility, disgust, fear, or the types of emotions that would pose some sort of danger to their offspring.
In the study from Franssen and his colleagues, which was published in Hormones and Behavior, another important skill that mothers develop is a heightened sense of smell. Not only can mother rats sense the odor of infant rats in general, they can specifically distinguish their own infant’s scent. This is the result of higher concentrations of cortisol, a corticosteroid hormone that increases blood pressure and blood sugar, and reduces immune responses.
Additionally, mother rodents have an advantage when it comes to memory tasks. Rats with mouths to feed were much better at remembering locations of food and water, compared to those in the study who did not have offspring. These newfound capabilities have been attributed to the numerous changes that occur in a mother’s brain, from larger neurons, increased numbers of dendrites and hormone receptors, to simply more neurons firing and communicating.