Natalie Angier in The New York Times:
A normal human baby, according to psychologists, will cry about two hours over the course of a day.
A notorious human crybaby, according to her older siblings, parents and the building superintendent, will cry for two hours every two hours, refusing to acknowledge any distinction between crying and other basic infant activities, like “being awake” or “breathing.” Current and former whine enthusiasts, take heart. It turns out that infant crying is not only as natural and justifiable as breathing: The two acts are physically, neurologically, primally intertwined. Scientists have discovered that the small cluster of brain cells in charge of fast, active respiration also grant a baby animal the power to cry.
Reporting in the Proceedings of the National Academy of Sciences, Carmen Birchmeier and Luis Hernandez-Miranda, of the Max Delbruck Center for Molecular Medicine in Berlin, and their colleagues showed that infant mice stripped of this key node — a mere 17,000 neurons, located in the evolutionarily ancient hindbrain — can breathe slowly and passively, but not vigorously or animatedly. When they open their mouths to cry, nothing comes out. As a result, their mothers ignore them, and the poorly breathing pups quickly die. “This was an astonishing finding,” Dr. Birchmeier said. “The mother could see the pups and smell the pups, but if they didn’t vocalize, it was as though they didn’t exist.” The new study is just one in a series of recent reports that reveal the centrality of crying to infant survival, and how a baby’s bawl punches through a cluttered acoustic landscape to demand immediate adult attention. The sound of an infant’s cry arouses a far quicker and stronger response in action-oriented parts of the adult brain than do similarly loud or emotionally laden noises, like a dog barking or a neighbor weeping. Scientists also have shown that the cries of many infant mammals share a number of basic sonic properties.