Where motherhood thrives, there too shall ye find the hormone oxytocin.
Oxytocin is plentifully present in a woman's body at the time of her child's birth -- and in its medicinal form, called Pitocin, it will even induce labor. It surges each time a mother's milk becomes available to nourish and comfort her baby. It spikes when she gazes at her infant, or hears its cry from another room.
But is oxytocin, sometimes referred to as the "love hormone," the cause of maternal behavior, a physical consequence of all those warm, nurturing thoughts and behaviors, or just a chemical along for the maternal ride? When it circulates in the body, oxytocin's volume and its physical effects can readily be measured and detected. But it's also present in the brain, and there, scientists are less clear about its action, and how it relates to that messy, hard-to-measure complex of behaviors that we know as motherhood.
A new study in mice sheds some light on how the hormone oxytocin works in the mammalian brain when maternal behavior first emerges. Researchers have shown that it binds to neurons in the left side of a female's auditory cortex -- the gray matter where sound is processed. There, it suppresses the neural "noise" that might ordinarily obscure a baby's cry.
The study was published Wednesday in the journal Nature.
Under the influence of oxytocin, the brains of postpartum female mice processed the peeps issued by a newborn as if they were a clarion call, seeking the baby out and providing warmth, comfort and nourishment.
That sets off a cascade of maternal learning that begets more maternal behavior, which begets more reciprocal affection and more learning, and yet more maternal behavior.
But the same behavior could be induced in adult female mice with no pups, and none of the experience of surging oxytocin that comes with childbirth. When researcher pumped extra oxytocin into their "virgin" brains, these mice quickly began to recognize barely audible distress calls from another mouse's pups who had been removed from their home nest.
These females would behave just as if they were the lost babies' mothers, finding the unrelated pups, picking them up by the scruffs of their necks and returning them to the nest. This learned behavior was permanent, researchers say; even when researchers plugged up the oxytocin receptors in the brains of these childless mice, these females continued to hear the plaintive peeps of lost pups and retrieve them.
"We found that oxytocin turns up the volume of social information processed in the brain," said Robert Froemke, the study's senior author and an assistant professor at New York University's Langone School of Medicine and its Skirball Institute of Biomolecular Medicine.
That makes oxytocin both more powerful and less powerful than many have believed, said Froemke. The hormone should be understood not as a fast-acting love potion, but rather as a well-timed neural nudge toward more social behavior.
At the same time, that neural nudge has a powerful range beyond facilitating maternal nurture, he said. One day, supplemental oxytocin could be shown useful to treat a wide range of psychological woes, from social anxiety, post-traumatic stress disorder, speech and language disorders, and even psychological issues stemming from child abuse.