Individual variation in body odor

Humans produce numerous volatile compounds from different areas of the body, either as a direct result of metabolic processes or indirectly via metabolismof resident microflora. Body odors vary between individuals, partly due to genetic differences, but odors of the same individual also vary across time due to environmental influences. We discuss how at least part of the genetic influence appears to be related to certain personality characteristics and to sexual orientation. We then review the current state of the art in terms of intraindividual variation, including effects of intrinsic factors, such as hormonal influences on body odor and environmental factors, namely effects of diet and certain diseases. Some of these changes can be perceived by other individuals and might therefore provide social cues of current motivational, nutritional, and health status. Finally, we discuss how specific odor profiles associated with certain infectious diseases and metabolic disorders can be used as a cheap and efficient medical screening tool

Licking and Liking: The Assessment of Hedonic Responses in Rodents

Affective processes are a key determinant of behaviour: At its simplest, liked stimuli are approached while disliked stimuli are avoided. Although assessing hedonic responses in nonverbal animals can be difficult, one relatively tractable approach relies on detailed analyses of rodents' consummatory behaviour. Rodents typically produce rhythmic sets of licks that can be grouped into clusters on the basis of the intervals between licks. The mean number of licks in a cluster (cluster size) is directly related to the concentration of palatable and unpalatable solutions. These relationships suggest that lick cluster size might be a useful index of an animal's hedonic reaction to the solution being consumed. I begin by reviewing studies of conditioned flavour preference and aversion that support the idea that lick cluster size can provide useful information about rats' hedonic reactions. I then describe how this methodology has been used to address previously intractable issues in the investigation of contrast effects as well as revealing an analogue of effort justification effects that, in humans, are commonly explained in terms of cognitive dissonance reduction. Finally, I consider how lick analysis might provide information about hedonic responses in animal models of human psychiatric disorders. In all these cases, how an animal did something was particularly informative about why it was doing it