Humans actively use behavioral synchrony such as dancing and singing when they intend to make affiliative relationships. Such advanced synchronous movement occurs even unconsciously when we hear rhythmically complex music. A foundation for this tendency may be an evolutionary adaptation for group living but evolutionary origins of human synchronous activity is unclear. Here we show the first evidence that a member of our closest living relatives, a chimpanzee, spontaneously synchronizes her movement with an auditory rhythm: After a training to tap illuminated keys on an electric keyboard, one chimpanzee spontaneously aligned her tapping with the sound when she heard an isochronous distractor sound. This result indicates that sensitivity to, and tendency toward synchronous movement with an auditory rhythm exist in chimpanzees, although humans may have expanded it to unique forms of auditory and visual communication during the course of human evolution.

In the introduction to this theme issue, Honing et al. suggest that the origins of musicality—the capacity that makes it possible for us to perceive, appreciate and produce music—can be pursued productively by searching for components of musicality in other species. Recent studies have highlighted that the behavioural relevance of stimuli to animals and the relation of experimental procedures to their natural behaviour can have a large impact on the type of results that can be obtained for a given species. Through reviewing laboratory findings on animal auditory perception and behaviour, as well as relevant findings on natural behaviour, we provide evidence that both traditional laboratory studies and studies relating to natural behaviour are needed to answer the problem of musicality. Traditional laboratory studies use synthetic stimuli that provide more control than more naturalistic studies, and are in many ways suitable to test the perceptual abilities of animals. However, naturalistic studies are essential to inform us as to what might constitute relevant stimuli and parameters to test with laboratory studies, or why we may or may not expect certain stimulus manipulations to be relevant. These two approaches are both vital in the comparative study of musicality.

Previous studies have shown that a variety of animals including humans are sensitive to social cues from others and shift their attention to the same objects attended to by others. However, little is known about how animals process conspecifics' and another species' actions, although primates recognize conspecific faces better than those of another species. In this study, using unrestrained eye-tracking techniques, we first demonstrated that conspecific social cues modulated looking behaviours of chimpanzees more than human cues, whereas human observers were equally sensitive to both species. Additionally, first pass gaze duration at the face indicates that chimpanzees looked at the chimpanzees' face longer than the human face, suggesting that chimpanzees might extract more referential information from a conspecific face. These results also imply that a unique ability for extracting referential information from a variety of social objects has emerged during human evolution.

Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism.

Although immune responses are essential to protect the body from infection, they can also harm tissues. Certain tissues and organs, including the eye, constitute specialized microenvironments that locally inhibit immune reactivity. Dedicator of cytokinesis protein 2 (DOCK2) is a Rac-specific guanine nucleotide exchange factor (GEF) that is predominantly found in hematopoietic cells. DOCK2 plays a key role in immune surveillance because it is essential for the activation and migration of leukocytes. mutations cause severe immunodeficiency in humans. We found that DOCK2-mediated Rac activation and leukocyte migration were effectively inhibited by cholesterol sulfate (CS), but not by cholesterol or other sulfated steroids. CS bound to the catalytic domain of DOCK2 and suppressed its GEF activity. Mass spectrometric quantification revealed that CS was most abundantly produced in the Harderian gland, which provides the lipids that form the oily layer of the tear film. Sulfation of cholesterol is mediated by the sulfotransferases SULT2B1b and, to a lesser extent, SULT2B1a, which are produced from the same gene through alternative splicing. By genetically inactivating, we showed that the lack of CS in mice augmented ultraviolet- and antigen-induced ocular surface inflammation, which was suppressed by administration of eye drops containing CS. Thus, CS is a naturally occurring DOCK2 inhibitor and contributes to the generation of the immunosuppressive microenvironment in the eye.

Researchers have investigated to what extent non-human primates understand others' attentional states, as this ability is considered an important prerequisite for theory of mind. However, previous studies using food requesting tasks have failed to show that non-human primates attribute perception to others as a function of their attentional states. One possible reason is that food requesting tasks may require subjects not only to take into account an experimenter's attentional state but also to direct it toward the food. The present study tested tufted capuchin monkeys' (Cebus apella) understanding of others' attentional states in a food requesting task. In the first situation, monkeys were required only to attract an experimenter's attention. In the second situation, the monkeys were required to both attract the experimenter's attention and direct it toward food on a table. The results revealed that capuchin monkeys showed evidence of understanding the experimenter's attentional variations only in the former condition. This suggests that previous tasks, requiring referential gestures, lacking in most non-human primates, failed to reveal sensitivity to human attentional states because the subjects might not have understood the requesting situation. In conclusion, capuchin monkeys can understand variations in others' attentional states, although this ability appears limited compared to what is seen in humans.

SummaryMonoamine neurotransmitters are released by specialized neurons regulating behavioral, motor, and cognitive functions. Although the localization of monoaminergic neurons in the brain is well known, the distribution and kinetics of monoamines remain unclear. Here, we generated a murine brain atlas of serotonin (5-HT), dopamine (DA), and norepinephrine (NE) levels using mass spectrometry imaging (MSI). We found several nuclei rich in both 5-HT and a catecholamine (DA or NE) and identified the paraventricular nucleus of the thalamus (PVT), where 5-HT and NE are co-localized. The analysis of 5-HT fluctuations in response to acute tryptophan depletion and infusion of isotope-labeled tryptophan in vivo revealed a close kinetic association between the raphe nuclei, PVT, and amygdala but not the other nuclei. Our findings imply the existence of a highly dynamic 5-HT-mediated raphe to PVT pathway that likely plays a role in the brain monoamine system.

The present study asked whether capuchin monkeys recognize human attentional states. The monkeys requested food from the experimenter by extending an arm (pointing) toward the baited one of two transparent cups. On regular trials the experimenter gave the food immediately to the monkeys upon pointing but on randomly inserted test trials she ignored the pointing for 5 s during which she displayed different attentional states. The monkeys looked at the experimenter's face longer when she looked at the monkeys than when she looked at the ceiling in Experiment 1, and longer when she oriented her head midway between the two cups with eyes open than when she did so with eyes closed in Experiment 2. However, the monkeys showed no differential pointing in these conditions. These results suggest that capuchins are sensitive to eye direction but this sensitivity does not lead to differential pointing trained in laboratory experiments. Furthermore, to our knowledge, this is the first firm behavioral evidence that non-human primates attend to the subtle states of eyes in a food requesting task.