Neural Correlates of Face and Object Perception in an Awake Chimpanzee (Pan Troglodytes) Examined by Scalp-Surface Event-Related Potentials

Abstract

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.

Neural representation of face familiarity in an awake chimpanzee

“…The signals were referenced to the forehead midline (FPz) and a ground electrode was positioned at the left earlobe (Fukushima et al, 2010). The electrodes were filled with Quick GEL and impedances were kept below 6 kΩ.…”

“…In particular, several research groups have reported neural examinations of chimpanzee visual processing (Boysen & Berntson, 1985; Fukushima et al, 2010; Parr et al, 2009). For instance, Parr and colleagues (Parr et al, 2009) conducted a functional neuroimaging study of chimpanzee face processing using positron emission tomography (PET).…”

“…Using this protocol, we previously revealed neural evidence that this chimpanzee discriminates human faces from other categories of objects, as there was a divergence of ERPs in response to face stimuli at approximately a 100 ms latency at posterior temporal regions (Fukushima et al, 2010). Furthermore, we demonstrated that chimpanzee neural activities are influenced by observing emotional expressions of conspecifics with an approximately 210 ms latency (Hirata et al, 2013).…”

Conceptual metaphorical mapping in chimpanzees (Pan troglodytes)

“…Decades of research have shown that neural representations of objects and entities exist in monkeys (Sigala et al, 2002), apes (Fukushima et al, 2010) and humans (Kourtzi and Kanwisher, 2001). The abilities of object representation and recognition further apply to social domains such as recognition of faces (Dahl et al, 2007; Dahl et al, 2013), conspecifics (Dahl et al, 2007), and ingroup-outgroup members (Pokorny and de Waal, 2009).…”

Brain response to affective pictures in the chimpanzee

“…After a long period of step-by-step training, we succeeded in measuring EEG in a fully-awake adult chimpanzee for the first time151617. In the present experiment, we measured ERPs in response to pictures which were a subset of the stimuli used in the chimpanzee memory experiment, in which enhanced memory for affective over neutral pictures was found12.…”