Mats J Olsson, Uppsala University

Many animals, insects as well as mammals, communicate through body "odors" that release specific internal reactions or behaviors. Although the existence of these so-called pheromones is well established in many species, research on human pheromones is in an unusual state. The lay public and industry presume that human pheromones exist, and the media frequently state this assumption as a fact. Thus, science has for a while found itself in the unusual position of presenting definitive evidence for the existence of human pheromones to a lay audience that already believed in their existence, but to a scientific audience that was quite skeptical. Although human research has just begun, current data point to a hitherto unstudied sensory mechanism, with potential effects on human psychological state and social behavior - effects that may range from those concerning sexuality and approach behavior to aggression and fear (McClintock, 2001). This proposal describes a series of studies on how men and women react on putative human pheromones with regard to psychological aspects, such as perceptual sensitivity, mood, attention, and approach behaviors.

Belov we list the primary results of 7 studies of which 5 are published in international peer-reviewed scientific journals.

We have shown that the mood in women and men can be affected by the exposure to putative human pheromones (androstadienone and estratetraenol)(Lundström et al 2005; Olsson et al., 2006). This has been a necessary replication of previous research from i.a. our lab. In addition, these studies have shown that the effect of the putative pheromone can be dependent on social context. Especially in on study the results were clear that women's mood improved from being exposed to androstadienone only if a male experimenter was interacting with the female participant (all involved testified to being heterosexual).

Another study on the putative male pheromone andorstadienone showed that the substance was processed faster by the brain than a comparable "ordinary" odor (Lundström, Olsson et al, 2006). In addition, we showed that the perception of the substance changed across the menstruation cycle. Women could detect the susbtance better during the ovulation phase compared to other phases( Lundström, McClintock & Olsson, 2006). These two studies altogether indicate that androstadienone is processed differently than control odors which supports the notion of androstadienone being a pheromone-like substance.

Two other studies focised on the effects of androstadienone on attention and on approach behavior (flirting). The first study we invetigated whether heterosequal men and women could detect a picture of a person of opposite sex on an array of other pcitures faster or more accurate than one of the the same sex. In addition we tested whether andostadienone would affect the performance in this attention test. No such effect could be determined. A second study studied the flirting behavior among male-female couples that were randomly formed from students that did not know each other before. The couple were asked to play a game and then discuss a moral dilemma for about 20 minutes. Half of the couples were exposed to androstadienone and the other half were exposed to a control odorant. Film sequences of the couples were analyzed for flirting behavior. Androstadienone hade only vague and somewhat inconsistent effects on flirting behavior. Interesingly, ovulating women were more flirty (but this did not inteact with exposure). This study is still under analsysis.

Yet another study was based on the fact that body odors are complex mixtures of 100s of odorants. How would the brain process an odor with another one being simultaneously present. A brain activation study (PET) showed that some part of the brain could differentiate between the case when we presented one and two odors. This should be seen in the light of that perceptually we can hardly tell whther there is one or two odorants behind the perception of an odor (Boyle et al, 2009).

Our work on pheromones hav also led to a publication in Science in which we present an hyopothesis (Lundstrom etl al. 2008). It starts from a recent study in the same journal that showed that couples formed by thrid and fourt couisng have an incresed reproductive success compared to closer or less closly related couples. based on the state of art, our hypothesis is that pairs of individuals will find the odor of the other to be more pleasant if they have a genetic similarlity (HLA-system) that approximates that of third and fourth cousin. This question is what we intend to pursue in the near future.

Altogether the project have given further support that endogenous odors, in particular androstadienone, are perceived differently from other non-endogenous odors: a priviliged access to the brain and more easily detected during ovulation. Also the results indicate that the effects that these putative pheromones may have in humans, can be dependent of the social context in which they occur.