The scent of the other women: Body odor-induced behavioral and physiological effects on face categorization.

In body odor research, the interaction of female donors and receivers is scarcely investigated. With the aim to investigate effects of female body odor in a competitive context, we tested 51 women divided into two groups (i.e., a competitive and a non-competitive group, based on verbal instructions). Between groups, we explored whether female body odor exposure (vs. masker odor) modulates emotion categorization (via RT variance and distribution) and physiological reactions (via instantaneous heart rate) in a task with dynamic male and female faces as either angry or happy. Women in the competitive group reported to feel more competitive and performed more accurately. They gathered more emotional information to categorize dynamic faces and when additionally exposed to female body odor, they showed a resistance to cardiac deceleration. Lapses of attention (via RT distribution) occurred irrespective of body odor exposure. Our results support the idea that female body odors, presented in a competitive context, contrast cardiac deceleration and, by tendency, modulate emotion categorization. Data are discussed in the context of chemosignaling and social interactions among women.

Odor Sensitivity After Intranasal Insulin Application Is Modulated by Gender.

Obesity constitutes a global health care problem, and often eating habits are to blame. For intervention, a thorough understanding of energy intake and expenditure is needed. In recent years, the pivotal role of insulin in connection to energy intake was established. Olfactory sensitivity may be a target of cerebral insulin action to maintain body weight. With this experiment, we aimed to explore the influence of intranasal insulin on olfactory sensitivity for the odors n-butanol and peanut in a placebo-controlled, double-blind setting in a within-subject design. All subjects participated in two experimental sessions on separate days and received either intranasal insulin or placebo in a pseudorandomized order. Application was followed by two olfactory threshold tests for n-butanol and peanut in a pseudorandomized order. After a single dose of intranasal insulin (40 IU) or placebo (0.4 ml), olfactory sensitivity for the odorants n-butanol and peanut were examined in 30 healthy normosmic participants (14 females). Measured blood parameters revealed no decrease in plasma glucose, however, insulin, leptin and cortisol levels were affected following intranasal application. Females' but not males' olfactory sensitivity for n-butanol was lower after intranasal insulin administration vs. placebo. In contrast, olfactory sensitivity for peanut was not influenced by intranasal insulin application. Our results indicate that the effects of cortical insulin levels on processing of specific odors is likely modulated by gender, as central increase of insulin concentration led to a reduced olfactory sensitivity for n-butanol in women only, which might be due to differentially regulated insulin and leptin signaling in men and women.

Chemosensory danger detection in the human brain: Body odor communicating aggression modulates limbic system activation.

Although the sense of smell is involved in numerous survival functions, the processing of body odor emitted by dangerous individuals is far from understood. The aim of the study was to explore how human fight chemosignals communicating aggression can alter brain activation related to an attentional bias and danger detection. While the anterior cingulate cortex (ACC) was seen involved in processing threat-related emotional information, danger detection and error evaluation, it still remains unknown whether human chemosignals communicating aggression can potentially modulate this activation. In the fMRI experiment, healthy male and female normosmic odor recipients (n=18) completed a higher-order processing task (emotional Stroop task with the word categories anger, anxiety, happiness and neutral) while exposed to aggression and exercise chemosignals (collected from a different group of healthy male donors; n=16). Our results provide first evidence that aggression chemosignals induce a time-sensitive attentional bias in chemosensory danger detection and modulate limbic system activation. During exposure to aggression chemosignals compared to exercise chemosignals, functional imaging data indicates an enhancement of thalamus, hypothalamus and insula activation (p<.05, FWE-corrected). Together with the thalamus, the ACC was seen activated in response to threat-related words (p<.001). Chemosensory priming and habituation to body odor signals are discussed.

Neural correlates of olfactory and visual memory performance in 3D-simulated mazes after intranasal insulin application.

This fMRI study intended to establish 3D-simulated mazes with olfactory and visual cues and examine the effect of intranasally applied insulin on memory performance in healthy subjects. The effect of insulin on hippocampus-dependent brain activation was explored using a double-blind and placebo-controlled design. Following intranasal administration of either insulin (40IU) or placebo, 16 male subjects participated in two experimental MRI sessions with olfactory and visual mazes. Each maze included two separate runs. The first was an encoding maze during which subjects learned eight olfactory or eight visual cues at different target locations. The second was a recall maze during which subjects were asked to remember the target cues at spatial locations. For eleven included subjects in the fMRI analysis we were able to validate brain activation for odor perception and visuospatial tasks. However, we did not observe an enhancement of declarative memory performance in our behavioral data or hippocampal activity in response to insulin application in the fMRI analysis. It is therefore possible that intranasal insulin application is sensitive to the methodological variations e.g. timing of task execution and dose of application. Findings from this study suggest that our method of 3D-simulated mazes is feasible for studying neural correlates of olfactory and visual memory performance.

You Smell Dangerous: Communicating Fight Responses Through Human Chemosignals of Aggression.

The ability to detect conspecifics that represent a potential harm for an individual represents a high survival benefit. Humans communicate socially relevant information using all sensory modalities, including the chemosensory systems. In study 1, we investigated whether the body odor of a stranger with the intention to harm serves as a chemosignal of aggression. Sixteen healthy male participants donated their body odor while engaging in a boxing session characterized by aggression-induction methods (chemosignal of aggression) and while performing an ergometer session (exercise chemosignal). Self-reports on aggression-related physical activity, motivation to harm and angry emotions selectively increased after aggression induction. In study 2, we examined whether receivers smelling such chemosignals experience emotional contagion (e.g., anger) or emotional reciprocity (e.g., anxiety). The aggression and exercise chemosignals were therefore presented to 22 healthy normosmic participants in a double-blind, randomized exposure during which affective/cognitive processing was examined (i.e., emotion recognition task, emotional stroop task). Behavioral results indicate that chemosignals of aggression induce an affective/cognitive modulation compatible with an anxiety reaction in the recipients. These findings are discussed in light of mechanisms of emotional reciprocity as a way to convey not only affective but also motivational information via chemosensory signals in humans.

Chemosensory Communication of Gender Information: Masculinity Bias in Body Odor Perception and Femininity Bias Introduced by Chemosignals During Social Perception.

Human body odor is a source of important social information. In this study, we explore whether the sex of an individual can be established based on smelling axillary odor and whether exposure to male and female odors biases chemosensory and social perception. In a double-blind, pseudo-randomized application, 31 healthy normosmic heterosexual male and female raters were exposed to male and female chemosignals (odor samples of 27 heterosexual donors collected during a cardio workout) and a no odor sample. Recipients rated chemosensory samples on a masculinity-femininity scale and provided intensity, familiarity and pleasantness ratings. Additionally, the modulation of social perception (gender-neutral faces and personality attributes) and affective introspection (mood) by male and female chemosignals was assessed. Male and female axillary odors were rated as rather masculine, regardless of the sex of the donor. As opposed to the masculinity bias in the odor perception, a femininity bias modulating social perception appeared. A facilitated femininity detection in gender-neutral faces and personality attributes in male and female chemosignals appeared. No chemosensory effect on mood of the rater was observed. The results are discussed with regards to the use of male and female chemosignals in affective and social communication.

The influence of alcohol intake and alcohol expectations on the recognition of emotions.

AIMS: To investigate the effects of actual and expected alcohol intake on the detection and interpretation of the basic emotions happiness and anger in facial expressions. METHODS: n = 102 healthy participants performed a dynamic emotion recognition task before and after receiving a drink which contained either a moderate alcohol dose or no alcohol in a double-blind design. RESULTS: The actual alcohol intake had no effect on detecting and interpreting facial expressions. However, subjects who expected to drink alcohol judged facial expressions significantly more often as happy. No effects were observable for the recognition of anger in facial expressions. CONCLUSION: Our results corroborate recent studies that found that the belief of consuming alcohol does not increase anger recognition or aggressive behavior but decreases aggression and social stress.