Memory for individuals: hamsters (Mesocricetus auratus) require contact to develop multicomponent representations (concepts) of others

In humans, individuals recognize other individuals by numerous types of independent information, such as the quality of the voice, appearance of the face, smell, gait, and posture. Humans also have integrated memories of others--that is, in response to a face or a voice the individual is recognized by name and other information about that individual is remembered. In many nonhuman species, individual recognition also occurs. Although observational studies suggest that individuals of some nonhuman species may be able to use several different cues for individual recognition, little experimental proof for this is available. Golden hamsters have at least 5 individually distinctive odors and they develop integrated, multi-odor memories (concepts) of familiar individuals, as shown by across-odor habituation experiments. Little is known, however, about the conditions that are necessary to develop such integrated memories. In these experiments we investigated what kinds of experiences were necessary for male hamsters to develop multiodor memories of females. The results show that exposure to all of the odors of another individual was not sufficient to develop such multiodor memories but that physical contact between the subjects and stimulus animals was necessary. Multiodor representations were developed after interactions with anesthetized individuals, confirming the finding that physical contact was important but also showing that interaction with an awake, behaving individual was not necessary to form multiodor representations of other individuals. We are not aware of experimental proof for integrated, multicomponant memories in any other nonhuman species.