For rodent¹ pups, bonding with mom isn't hard-wired in the womb（子宫） . It develops over the first few weeks of life, which is achieved by their maturing sense of smell, possibly allowing these mammals a survival advantage by learning to identify mother, siblings², and home. Blending electrophysiological, biochemical, and behavioral experiments, Minghong Ma, PhD, an associate Professor of Neuroscience at the University of Pennsylvania School of Medicine, led a study published in a recent issue of the Journal of Neuroscience. With students Anderson Lee and Jiwei He, she demonstrated that neurons in the noses of mice mature after birth.

Using patch-clamping – a technique that measures electrical signals at the cellular³ level -- Ma's team found that between birth and day 30 of development, normal neurons become six times more sensitive to their sibling's scent⁴, in this case, a fragrance⁵（香味，芬芳） called lyral. In addition, the mice transition from a relative indiscriminate（任意的） response to different odors（气味，名声） to being highly attuned⁶ to one specific smell. They also respond to that specific odor with a faster speed over time.

The olfactory⁷（嗅觉的） marker protein (OMP) likely mediates⁸ this developmental maturation. In olfactory sensory⁹ neurons lacking OMPs, response fails to speed up over 30 days as compared to normal neurons. The authors suggest this could be due to altered intracellular（细胞内的） communication, since loss of the protein is associated with decreased phosphorylation（磷酸化作用） of an associated enzyme¹⁰ called adenylate cyclase, a key player in the chemical signaling underlying¹¹ the sense of smell.

The team also used a novel behavioral assay¹² to illustrate¹³ one consequence of mistakes in this cellular maturation process. Normal mouse pups, given the choice between their mother and an unrelated, lactating female, will choose to huddle¹⁴ with or suckle their mother 78 percent of the time. But in the absence of OMP, newborn mice fail to make that distinction.

According to Ma, the maturation of olfaction in early development could offer animals that need nursing and care for a long time before maturing (altricial species, including some mammals) a survival advantage. Rather than being hard-wired at birth, Ma says, they learn to identify their surroundings and their family. "They actually learn to find their mother, home, and siblings, and to stay alive," she says. But whether the same is true of human infants, of course, remains¹⁵ an open question.

One key question yet to be addressed, Ma says, is the mechanism¹⁶ underlying this olfactory tuning¹⁷ process. How, for instance, do the cells develop a faster response speed? How do they get so good at focusing on just one odorant（有气味的东西） to the exclusion¹⁸ of all others? And can this process be modulated¹⁹ by early experience? The answers to those questions, she says, could possibly provide tools to influence the bonding between mother and child in early development, and even promote social interactions in autistic（孤僻的） children.