The use of nasal skin temperature measurements in studying emotion in macaque monkeys.

Using an infrared thermographic system, we have demonstrated, as previously reported, that temperatures in the nasal region of macaque monkeys decrease during negative emotional states, such as when facing a threatening person. In this study, we explored the usefulness of measuring nasal skin temperatures in studies of monkey emotions as manifested by conspecific emotional behaviors and expressions. We measured nasal skin temperatures of rhesus monkeys (Macaca mulatta) in response to video clips, all showing monkeys: a raging individual (Experiment 1), three distinct emotional expressions (Experiment 2), and only faces or voices representing a threat (Experiment 3). We found that nasal skin temperatures significantly decreased in response to a threatening stimulus, even when the stimulus was a 2D image with digitized sound, similar to those used in many psychological or neurophysiological studies on animal emotion. Moreover, species-specific aggressive threats invariably elicited a decrease in nasal skin temperatures and skin conductance responses; however, screams or coos did not elicit this response. Simultaneous perception of both facial expressions and vocalizations induced a more prominent decrease in nasal skin temperatures than did the perception of facial expressions or vocalizations alone. Taken together, these data suggest that decreased nasal skin temperatures should be added to the list of indicators of emotional states in animals.