Monkey see, monkey feel? Marmoset reactions towards conspecifics' arousal

Consolation has been observed in several species, including marmoset monkeys, but it is often unclear to what extent they are empathy-based. Marmosets perform well in at least two of three components of empathy-based consolation, namely understanding others and prosociality, but it is unknown to what extent they show matching with others. We, therefore, tested whether non-aroused individuals would become aroused themselves when encountering an aroused group member (indicated by piloerection of the tail). We found a robust contagion effect: group members were more likely to show piloerection themselves after having encountered an aroused versus relaxed conspecific. Moreover, group members offered consolation behaviours (affiliative approaches) towards the aroused fellow group members rather than the latter requesting it. Importantly, this pattern was shown by both aroused and non-aroused individuals, which suggests that they did not do this to reduce their own arousal but rather to console the individual in distress. We conclude that marmosets have all three components of empathy-based consolation. These results are in line with observations in another cooperative breeder, the prairie vole.

Interspecies activation correlations reveal functional correspondences between marmoset and human brain areas

The common marmoset has enormous promise as a nonhuman primate model of human brain functions. While resting-state functional MRI (fMRI) has provided evidence for a similar organization of marmoset and human cortices, the technique cannot be used to map the functional correspondences of brain regions between species. This limitation can be overcome by movie-driven fMRI (md-fMRI), which has become a popular tool for noninvasively mapping the neural patterns generated by rich and naturalistic stimulation. Here, we used md-fMRI in marmosets and humans to identify whole-brain functional correspondences between the two primate species. In particular, we describe functional correlates for the well-known human face, body, and scene patches in marmosets. We find that these networks have a similar organization in both species, suggesting a largely conserved organization of higher-order visual areas between New World marmoset monkeys and humans. However, while face patches in humans and marmosets were activated by marmoset faces, only human face patches responded to the faces of other animals. Together, the results demonstrate that higher-order visual processing might be a conserved feature between humans and New World marmoset monkeys but that small, potentially important functional differences exist.

Frontal cortex activity underlying the production of diverse vocal signals during social communication in marmoset monkeys

Vocal communication is essential for social behaviors in humans and many non-human primates. While the frontal cortex has been shown to play a crucial role in human speech production, its role in vocal production in non-human primates has long been questioned. Recent studies have shown activation in single neurons in the monkey frontal cortex during vocal production in relatively isolated environment. However, little is known about how the frontal cortex is engaged in vocal production in ethologically relevant social context, where different types of vocal signals are produced for various communication purposes. Here we studied single neuron activities and local field potentials (LFP) and in the frontal cortex of marmoset monkeys while the animal engaged in vocal exchanges with other conspecifics in a social environment. Marmosets most frequently produced four types of vocalizations with distinct acoustic structures, three of which were typically not produced in isolation. We found that both single neuron activities and LFP were modulated by the production of each of the four call types. Moreover, the neural modulations in the frontal cortex showed distinct patterns for different call types, suggesting a representation of vocal signal features. In addition, we found that theta-band LFP oscillations were phase-locked to the phrases of twitter calls, which indicates the coordination of temporal structures of vocalizations. Our results suggested important functions of the marmoset frontal cortex in supporting the production of diverse vocalizations in vocal communication.

Do marmosets understand others’ conversations? A thermography approach

What information animals derive from eavesdropping on interactions between conspecifics, and whether they assign value to it, is difficult to assess because overt behavioral reactions are often lacking. An inside perspective of how observers perceive and process such interactions is thus paramount. Here, we investigate what happens in the mind of marmoset monkeys when they hear playbacks of positive or negative third-party vocal interactions, by combining thermography to assess physiological reactions and behavioral preference measures. The physiological reactions show that playbacks were perceived and processed holistically as interactions rather than as the sum of the separate elements. Subsequently, the animals preferred those individuals who had been simulated to engage in positive, cooperative vocal interactions during the playbacks. By using thermography to disentangle the mechanics of marmoset sociality, we thus find that marmosets eavesdrop on and socially evaluate vocal exchanges and use this information to distinguish between cooperative and noncooperative conspecifics.