Chemosignaling emotions: What a smell can tell

Our eyes and ears mainly register the continuous stream of social stimuli impinging on us; vision and hearing are the typical modalities one would associate with social communication. However, the current dissertation is concerned with a particular branch of social communication, namely that of emotional states, and it examines the role of a potentially neglected modality in human communication: the sense of smell. As there is substantial overlap in limbic brain regions processing emotional and olfactory information, olfaction is often considered to be the “most emotional” sense. Indeed, odors can easily become associated with emotional experiences (e.g., fear). This dissertation constitutes a systematic examination of whether fear can be communicated from sender to receiver via body odor, by testing hypotheses derived from an embodied social communication framework. Chapter 3 showed that receivers exposed to the body odor of fearful individuals (vs. neutral, disgust) showed signs of emotional contagion evidenced by fearful facial expression and vigilant behavior (more effective eye scanning, increased sniffing behavior, enhanced accuracy during visual search). Chapter 4, 5, and 6 were aimed at examining the boundary conditions of the chemical communication of fear. More specifically, Chapter 4 examined whether olfactory information (fear-related and neutral) would be overridden by (in)congruent, simultaneously presented audiovisual information. Interestingly, fear-related information was communicated to receivers regardless of whether fear was communicated via the audiovisual or olfactory modality. Chapter 5 showed that women who are generally more sensitive to odors and emotions emulated the fearful state of the senders, whereas men did not. Chapter 6 showed that the capability to communicate by means of olfactory signals may not only be limited to negative emotions, but could be extended to (high arousal) positive ones as well. Chapter 7 closed in on the mechanisms of the chemical communication of fear. As sweat glands in the armpit region have receptors for adrenalin, it was expected that “fear odor” would be produced as a function of adrenalin release. Indeed, what drove the chemical transfer of fear from sender to receiver was the product of the rapid stress system, adrenalin, rather than cortisol resulting from the slow stress system. Overall, the combined set of studies indicated that humans have the capacity to become emotionally affected by body odors produced during distinctive emotional states. Hence, human odors can serve as a communicative medium by transferring dynamic emotional states from a sender to a receiver.