One theory is that these changes may have an evolutionary benefit to strengthen the communication between a mother and her infant. They may improve a mother’s ability to help a child to first understand the outer world, and then learn how to make sense of internal sensations.

In keeping with evolution, animal studies show that the neural circuitry changes of pregnancy provide a crucial adaptation, thought to heighten a mother’s mental and emotional focus to this new and hugely dependent creature in her life. At the same time, as both neuroscience and psychological research on attachment theory suggest, a human mother’s brain enhances its empathetic capacities, strengthening a mother’s ability to pick up on a baby’s nonverbal communications through facial expressions and cries.

Of course, parents who do not go through pregnancy — including fathers, adoptive parents and L.G.B.T.Q. parents whose partners give birth — also experience psychological and physiological attachment, which some researchers have studied. But “daddy brain” is rarely discussed in a cultural or scientific context in association with cognitive decline.

Meanwhile, the cultural belief in “mommy brain” is so powerful that some studies have shown that pregnant women who walked into an experiment describing themselves as cognitively fuzzy were found in the lab to perform at a much higher level than what they reported. Were the cognitive changes just in their heads, or are our medical formulations missing something? In addition to the unscientific myths about hormonal women being best suited for the home and hearth, what else has propelled this broader misinterpretation about what “mommy brain” is and isn’t?

It’s not only the physiology of pregnancy that changes the brain, but also the lived experience of parenting. Brain scans cannot yet factor in all of the ways becoming a parent may change you, from the way you sleep to the way you exercise and even socialize. As Helena Rutherford, an assistant professor at the Yale Child Study Center said, “Individual differences factor into parental brain studies. Like other areas of psychology and neuroscience, there isn’t a one-size-fits-all approach.”

To have a full understanding of how pregnancy and motherhood affect women, we need to look not just at the brain, but also at the mind. The mind, like consciousness, arises out of our biology, but it is influenced by so much more than cells and signals: Our emotions, memories, relationships, even unconscious mental life also play a part.

“If we have learned anything,” the U.C.L.A. psychologist Martie Haselton writes in her book “Hormonal: The Hidden Intelligence of Hormones — How They Drive Desire, Shape Relationships, Influence Our Choices and Make Us Wiser,” it is that “although biology plays a role, our social context (and our agency to reflect and make choices) matters just as much.”