A recent study demonstrated that having infants in the family group could promote altruistic behavior of marmoset. This work, published in Current Biology, was performed by the researchers from Dr. GONG Neng's team and Dr. LIANG Zhifeng's team at the Institute of Neuroscience, Center for Excellence in Brain Science and Intelligence Technology of the Chinese Academy of Sciences.     

Previous studies in altruistic behavior were mainly performed in human with noninvasive techniques, and very few were done in rodents due to their relatively simple social behavior and uncommon altruistic behavior.

Common marmoset (Callithrix jacchus), one kind of New World monkeys, has attracted much attention as a useful animal model in neuroscience. They naturally live in monogamous family groups, exhibit cooperative breeding and rich pro-social behaviors, such as sharing food with others. These features indicate that marmoset may be a useful non-human primate model for studying altruistic behavior. 

In this study, the researchers established a novel rescue paradigm to evaluate marmoset’s altruistic behavior and found that marmoset parents and older siblings show strong motivation to rescue young infants rather than their favorite food.

This infant-rescue behavior declined as infants grew up, and marmoset parents did not rescue juvenile marmosets beyond two months of age. Infant calls alone could trigger these parents' rescue behaviors. The marmoset parents showed little rescue of each other, but young infants or infant calls could also induce parents' mutual rescue. Moreover, these infant- and mate- rescue behaviors occurred only in family groups that currently had young infants.

To explore the underlying neural mechanism, the researchers performed functional magnetic resonance imaging (fMRI) on awaked marmosets. They found that infant’s vocalization compared to its scrambled version, but not juvenile’s vocalization, could elicit activation of specific brain areas including auditory and insular cortices in adult marmoset parents currently having infant in their family groups, while such activation was absent in marmosets not having infants.

This work showed that marmoset could be a useful non-human primate model to study altruistic behavior, and demonstrated a specific infant-induced rescue behavior in marmoset families. Such infant-induced modification of neural activity offers a window for examining the neural basis of altruistic behaviors in marmoset monkeys.