Food sharing among chimpanzees is known to occur particularly between mothers and infants and has been proposed to be a form of parental investment. To explore the function of food sharing, it is essential to know how and what is transferred to an infant from its mother. We investigated details of interactions leading to food transfer and characteristics of items transferred in three mother-infant ( < 2 years old) pairs in captivity. We gave one kind of fruit or vegetable to a mother and observed interactions between the mother and her infant. Tested items consisted of familiar and novel foods for infants. Two patterns of direct food transfer, so-called sharing, were recognized: (1) "infant-initiated sharing" in which the infant attempted to take food and the mother did not resist, and (2) "mother-initiated sharing" in which the mother spontaneously offered a part of her food without the infant's attempts to take it. There were clear differences in the characteristics of items transferred in these two patterns of sharing. In infant-initiated sharing, palatable parts of the same food that the mother was eating were transferred. In contrast, in mother-initiated sharing, only unpalatable parts of food in the mother's possession were transferred. Mothers seemed to be reluctant to give nutritious foods to their infants during this study period. Infants, rather than mothers, were responsible for initiating and experiencing the diversity of adult foods in chimpanzees.

BackgroundFor decades, the chimpanzee, phylogenetically closest to humans, has been analyzed intensively in comparative cognitive studies. Other than the accumulation of behavioral data, the neural basis for cognitive processing in the chimpanzee remains to be clarified. To increase our knowledge on the evolutionary and neural basis of human cognition, comparative neurophysiological studies exploring endogenous neural activities in the awake state are needed. However, to date, such studies have rarely been reported in non-human hominid species, due to the practical difficulties in conducting non-invasive measurements on awake individuals.Methodology/Principal FindingsWe measured auditory event-related potentials (ERPs) of a fully awake chimpanzee, with reference to a well-documented component of human studies, namely mismatch negativity (MMN). In response to infrequent, deviant tones that were delivered in a uniform sound stream, a comparable ERP component could be detected as negative deflections in early latencies.Conclusions/SignificanceThe present study reports the MMN-like component in a chimpanzee for the first time. In human studies, various ERP components, including MMN, are well-documented indicators of cognitive and neural processing. The results of the present study validate the use of non-invasive ERP measurements for studies on cognitive and neural processing in chimpanzees, and open the way for future studies comparing endogenous neural activities between humans and chimpanzees. This signifies an essential step in hominid cognitive neurosciences.

BackgroundThe neural system of our closest living relative, the chimpanzee, is a topic of increasing research interest. However, electrophysiological examinations of neural activity during visual processing in awake chimpanzees are currently lacking.Methodology/Principal FindingsIn the present report, skin-surface event-related brain potentials (ERPs) were measured while a fully awake chimpanzee observed photographs of faces and objects in two experiments. In Experiment 1, human faces and stimuli composed of scrambled face images were displayed. In Experiment 2, three types of pictures (faces, flowers, and cars) were presented. The waveforms evoked by face stimuli were distinguished from other stimulus types, as reflected by an enhanced early positivity appearing before 200 ms post stimulus, and an enhanced late negativity after 200 ms, around posterior and occipito-temporal sites. Face-sensitive activity was clearly observed in both experiments. However, in contrast to the robustly observed face-evoked N170 component in humans, we found that faces did not elicit a peak in the latency range of 150–200 ms in either experiment.Conclusions/SignificanceAlthough this pilot study examined a single subject and requires further examination, the observed scalp voltage patterns suggest that selective processing of faces in the chimpanzee brain can be detected by recording surface ERPs. In addition, this non-invasive method for examining an awake chimpanzee can be used to extend our knowledge of the characteristics of visual cognition in other primate species.