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As with humans, vocal communication is an important social tool for nonhuman primates. Common marmosets (Callithrix jacchus) often produce whistle-like 'phee' calls when they are visually separated from conspecifics. The neural processes specific to phee call perception, however, are largely unknown, despite the possibility that these processes involve social information. Here, we examined behavioral and whole-brain mapping evidence regarding the detection of individual conspecific phee calls using an audio playback procedure. Phee calls evoked sound exploratory responses when the caller changed, indicating that marmosets can discriminate between caller identities. Positron emission tomography with [ 18 F] fluorodeoxyglucose revealed that perception of phee calls from a single subject was associated with activity in the dorsolateral prefrontal, medial prefrontal, orbitofrontal cortices, and the amygdala. These findings suggest that these regions are implicated in cognitive and affective processing of salient social information. However, phee calls from multiple subjects induced brain activation in only some of these regions, such as the dorsolateral prefrontal cortex. We also found distinctive brain deactivation and functional connectivity associated with phee call perception depending on the caller change. According to changes in pupillary size, phee calls from a single subject induced a higher arousal level compared with those from multiple subjects. These results suggest that marmoset phee calls convey information about individual identity and affective valence depending on the consistency or variability of the caller. Based on the flexible perception of the call based on individual recognition, humans and marmosets may share some neural mechanisms underlying conspecific vocal perception.

Background: The common marmoset has been used as an experimental animal for various purposes. Because its average weight ranges from 250 to 500 g, weight loss quickly becomes critical for sick animals. Therefore, effective and non-stressful treatment for chronic diseases, including diarrhoea, is essential., Case Presentation: We report a case in which faecal microbiota transplantation (FMT) led to immediate recovery from chronic and recurrent diarrhoea caused by Clostridium difficile infection. A male common marmoset experienced chronic diarrhoea after antibiotic treatments. The animal experienced severe weight loss, and a faecal sample was confirmed to be C. difficile-positive but was negative for protozoa. Metronidazole was partially effective at the first administration but not after the recurrence of the clinical signs. Then, oral FMT was administered to the subject by feeding fresh faeces from healthy individuals mixed with the marmoset's usual food. We monitored the faeces by categorization into four groups: normal, loose, diarrhoea, and watery. After the first day of FMT treatment, the marmoset underwent a remarkable recovery from diarrhoea, and after the fourth day of treatment, a test for C. difficile was negative. The clinical signs did not recur. The marmoset recovered from sinusitis and bilateral dacryocystitis, which also did not recur, as a by-product of the improvement in its general health caused by the cessation of diarrhoea after the FMT., Conclusion: This is the first reported case of successful treatment of a marmoset using oral FMT. As seen in human patients, FMT was effective for the treatment of recurrent C. difficile infection in a captive marmoset.