In the study, which appeared in the journal PLoS ONE , researchers switched mice pups born to previously nurturing mothers with babies born to negligent mothers. Good mouse mothers suckle, groom, and protect their pups, according to the study authors, while deadbeat mouse moms fail to follow through with the proper levels of attention.
Surprisingly, the researchers observed that while nurturing moms cared for foster babies born to other nurturing females, several became increasingly neglectful when presented with pups born to a previously neglectful mother. "In some cases the previously nurturing mothers would actively scatter the pups away from the nest, suggesting a negative cue from the pups or a lack of a positive cue," said lead researcher and UW-Madison zoology professor Stephen Gammie. This shows that offspring can impact the behavior of mothers, Gammie said, and that maternal care is not only about genetics.
The researchers also analyzed brains of neglectful and nurturing mothers shortly after birth. In several brain regions of negligent mothers, they found higher levels of activity as well as abnormal dopamine signaling. These females might have the physical capability to take care of their pups, but are lacking in motivation, Gammie said.
"It's been shown in a number of studies that parental care is a motivated, reward-related behavior," he said. "And it has been suggested by others that some aspects of child neglect in humans could result from a lack of reward of an offspring to the parent."
The study's results are timely, as a report published in early April by the Centers for Disease Control and Prevention on American children found that, among infants less than a week old, almost 70 percent of nonfatal mistreatment cases were instances of neglect.
Anthony P. Auger, another of the study's authors, said it was too early to understand how their findings will translate to humans, but for the mice "the difference is quite dramatic in the brain. Dopamine is likely not the only thing being disrupted, but it is an important starting signaling pathway to pursue."