Empathic Cognitions Affected by Undetectable Social Chemosignals: An EEG Study on Visually Evoked Empathy for Pain in an Auditory and Chemosensory Context

Increased sensorimotor activity during categorisation of emotionally ambiguous faces

Actions are rarely devoid of emotional content. Thus, a more complete picture of the neural mechanisms underlying the mental simulation of observed actions requires more research using emotion information. The present study used high-density electroencephalography to investigate mental simulation associated with facial emotion categorisation. Alpha-mu rhythm modulation was measured at each frequency, from 8 Hz to 13 Hz, to infer the degree of sensorimotor simulation. Results suggest the sensitivity of the sensorimotor activity to emotional information, because (1) categorising static images of neutral faces as happy or sad was associated with stronger suppression in the central region than categorising clearly happy faces, (2) there was preliminary evidence indicating that the strongest suppression in the central region was in response to neutral faces, followed by sad and then happy faces and (3) in the control task, which required categorising images with the head oriented right, left, or forward as right or left, differences between conditions showed a pattern more indicative of task difficulty rather than sensorimotor engagement. Dissociable processing of emotional information in facial expressions and directionality information in head orientations was further captured in beta band activity (14-20 Hz). Stronger mu suppression to neutral faces indicates that sensorimotor simulation extends beyond crude motor mimicry. We propose that mu rhythm responses to facial expressions may serve as a biomarker for empathy circuit activation. Future research should investigate whether atypical or inconsistent mu rhythm responses to facial expressions indicate difficulties in understanding or sharing emotions.

Sexual Orientation Affects Neural Responses to Subtle Social Aggression Signals

The current series of studies are the first to examine brain responses to social aggression signals as a function of male and female sexual orientation. For the first set of studies (1a, 1b), axillary sweat had been collected from 17 heterosexual men and 17 heterosexual women aggressively responding to frustrating opponents (aggression condition) and while playing a construction game (control condition). Sweat samples were pooled according to sex and condition, and presented via a constant flow olfactometer to 17 gay and 23 heterosexual men (Study 1a), and 19 lesbian and 25 heterosexual women (Study 1b). Ongoing EEG was recorded from 61 scalp locations, chemosensory event-related potentials (CSERPs; P2, P3-1, P3-2) were analyzed, and neuronal sources calculated (low resolution electromagnetic tomography). Within the second set of studies (2a, 2b), pictures of males' and females' weak angry and neutral facial expressions were presented to 21 gay and 23 heterosexual men (Study 2a), and 19 lesbian and 26 heterosexual women (Study 2b), and ERPs (N170, P3) were analyzed. Gay men showed larger P3-1 amplitudes than heterosexual men upon presentation of male aggression sweat, accompanied by activation of the right inferior frontal gyrus (IFG, BA 10). Gay men also displayed longer N170 latencies in response to men's compared to women's angry facial expressions, while heterosexual men did not. In women, sexual orientation did not affect the processing of aggression sweat or anger expressions. Gay men showed preferential processing of chemosensory aggression signals (P3-1 amplitudes), indicating fine-tuned socioemotional sensitivity, related to activation of brain areas involved in emotion regulation (IFG). They further process the relative relevance of visual aggression signals (N170 latency). These results were in line with theories proposing a common evolutionary pathway for same-sex attraction and traits easing social integration.

Can you smell my stress? Influence of stress chemosignals on empathy and emotion recognition in depressed individuals and healthy controls

Human body odors contain chemical signals that play a key role in our non-verbal communication regarding health, genetic identity, immune system, fitness, and emotional state. Studies on human chemosignaling in individuals with psychiatric diseases are scarce but indicate altered smell perception and emotion recognition in depressed individuals. In the present project, we aimed to investigate the influence of chemosensory substances in social stress sweat on emotion recognition, perspective taking, affective responsiveness as well as stress level in healthy and depressed individuals. Therefore, chemosensory stimuli (sweat samples from Trier social stress test (TSST) and friendly-TSST (fTSST)) were obtained from 39 healthy participants (19 females). In a next step, chemosensory stimuli and an odor-free blank (cotton pad) were used to stimulate another group of 40 healthy participants (20 females) and 37 individuals with depression (24 females). Those stimuli were examined regarding their influence on subjective feelings of stress, emotion perception and empathic reactions using an empathy test. Furthermore, physiological data (breathing, heart rate, skin conductance response, stress hormones) of the participants were collected during chemosensory stimulation. Depressed individuals improved their ability of perspective taking and affective responsiveness for the emotion grief when presented with stress chemosignals compared to no chemosignals. Healthy individuals remained unaffected regarding perspective taking and affective responsiveness. Both depressed and healthy individuals showed no increased stress hormone cortisol and α-amylase values during the social stress chemosignals condition, but reduced values for fTSST condition compared to no chemosignals respectively. The results imply that stress chemosignals do not trigger a stress reaction, but for depressed individuals they lead to a better emotion assessment for grief. This research contributes to a deeper understanding of the effects of social stress chemosignals on healthy and depressed individuals. Knowing the impact of human chemosignals on emotional processing is crucial for a better understanding of non-verbal human interaction.

Past, Present, and Future of Human Chemical Communication Research

Although chemical signaling is an essential mode of communication in most vertebrates, it has long been viewed as having negligible effects in humans. However, a growing body of evidence shows that the sense of smell affects human behavior in social contexts ranging from affiliation and parenting to disease avoidance and social threat. This article aims to (a) introduce research on human chemical communication in the historical context of the behavioral sciences; (b) provide a balanced overview of recent advances that describe individual differences in the emission of semiochemicals and the neural mechanisms underpinning their perception, that together demonstrate communicative function; and (c) propose directions for future research toward unraveling the molecular principles involved and understanding the variability in the generation, transmission, and reception of chemical signals in increasingly ecologically valid conditions. Achieving these goals will enable us to address some important societal challenges but are within reach only with the aid of genuinely interdisciplinary approaches.

An examination of mindfulness on Mu suppression and pain empathy and its relation to trait empathy

There have been multiple benefits reported from the practice of mindfulness meditation. Recently social functioning, including empathy, has emerged as one such possible benefit. However, the literature is mixed and it is unknown if mindfulness has an effect on the neural mechanism involved in empathy. Therefore, we conducted a large-scale experimental study involving over 100 participants that were either enrolled in a behavioral or EEG experiment to examine pain empathy and mu suppression, respectively. We also measured state and trait mindfulness and trait empathy. Results did not show a change in pain empathy or mu suppression in response to an acute mindfulness manipulation. However, pain empathy responses were able to be predicted significantly better when the component of state mindfulness involving decentering was incorporated into a regression model compared to trait empathy alone. Also, trait empathy was related to trait mindfulness. Collectively, state decentering may be involved in increased pain empathy, while trait mindfulness appears more related to general trait empathy. Further research is warranted to better understand the potential benefit a brief mindfulness meditation may produce in the realm of brain activity and social functioning.

You See What You Smell: Preferential Processing of Chemosensory Satiety Cues and Its Impact on Body Shape Perception

The current study examines neural responses to satiety- and fasting-related volatiles and their effect on the processing of body shapes. Axillary sweat was sampled with cotton pads from 10 individuals after 12 h of fasting, and after having consumed a standard breakfast. Pure cotton pads served as the control. The chemosensory stimuli were presented to 20 participants (via a constant-flow olfactometer) exclusively, and additionally as context to images of overweight and underweight avatars. EEG was recorded (61 electrodes), and chemosensory (CSERPs; P1, N1, P2, P3) and visual event-related potentials (VERPs; N1, P2, P3a, P3b) were analyzed. The amplitudes of all positive CSERP components differed more strongly from cotton in response to chemosensory satiety cues as compared to fasting cues (P1: p = 0.023, P2: p = 0.083, P3: p = 0.031), paralleled by activity within the middle frontal and temporal gyrus. Overweight compared to underweight body shapes tended to elicit larger VERP P2 amplitudes (p = 0.068), and chemosensory satiety cues amplified the VERP amplitudes in response to any body shape (P2, P3a, P3b; all p_s ≤ 0.017) as compared to the cotton control. The results indicate that chemosensory satiety cues transmit complex social information, overriding the processing of analogous visual input.

It's trust or risk? Chemosensory anxiety signals affect bargaining in women

It is well documented how chemosensory anxiety signals affect the perceiver's physiology, however, much less is known about effects on overt social behavior. The aim of the present study was to investigate the effects of chemosensory anxiety signals on trust and risk behavior in men and women. Axillary sweat samples were collected from 22 men during the experience of social anxiety, and during a sport control condition. In a series of five studies, the chemosensory stimuli were presented via an olfactometer to 214 participants acting as investors in a bargaining task either in interaction with a fictitious human co-player (trust condition) or with a computer program (risk condition). It could be shown that chemosensory anxiety signals reduce trust and risk behavior in women. In men, no effects were observed. Chemosensory anxiety is discussed to be transmitted contagiously, preferentially in women.

Chemosensory communication of aggression: women's fine-tuned neural processing of male aggression signals

The current study is the first to examine the central nervous processing of aggression chemosignals within men and women by means of chemosensory event-related potential (CSERP) analysis. Axillary sweat was collected from 17 men and 17 women participating in a competitive computer game (aggression condition) and playing a construction game (control condition). Sweat samples were pooled with reference to donor gender and condition, and presented to 23 men and 25 women via a constant flow olfactometer. Ongoing electroencephalogram was recorded from 61 scalp locations, CSERPs (P2, P3-1, P3-2) were analysed and neuronal sources calculated (low-resolution electromagnetic tomography, LORETA). Women, especially, showed larger P3-1 and P3-2 amplitudes in response to male as compared with female aggression signals (all p values < 0.01). The peak activation of this effect was related to activity within the dorsomedial prefrontal cortex (Brodmann area 8). As male aggression commonly targets physical harm, the competence of the human brain to sensitively detect male aggression signals is considered to be highly adaptive. The detection of male aggression signals seems to be of higher importance for women than for men. It is suggested that the processing of male aggression signals in women induces an immediate response selection. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Mu-Suppression as an Indicator of Empathic Processes in Lesbian, Gay, and Heterosexual Adults

Self-reported empathy differs with gender and sexual orientation. The current study investigated whether mu-suppression, reflecting brain activity especially related to state empathy, also is modulated by gender and sexual orientation. Pictures of painful and non-painful actions were presented to 20 lesbians, 20 gay men, 20 heterosexual men and 20 heterosexual women, while EEG was recorded. Individual peak frequencies of mu-activity (electrodes C3, C4) were detected within the 6-11 Hz band for each participant, and mu-suppression indices were calculated. Further, verbal indicators of state empathy (pain ratings) and compassion were assessed. Only heterosexual individuals showed the typical pattern of enhanced mu-suppression in response to painful relative to non-painful pictures. Lesbian women and gay men did not show a differential mu-response. Moreover, they felt less compassion compared to heterosexual individuals. In line with this finding, the more compassion the participants reported, the stronger the mu-suppression in response to painful relative to non-painful pictures was. Pain ratings did not vary with sexual orientation. The lesser compassion reported by lesbian women and gay men is discussed as a mediator of their non-differential mu-suppression response. It is hypothesized that this pattern might relate to gay men and lesbian women tending to perceive the anonymous depicted actors as outgroup members, hence showing less compassion and reduced mu-suppression. As empathy is often related to negative feelings (empathic stress), a clear distinction between individuals to empathize with versus individuals not to emphasize with may well be an adaptive feature in same-sex oriented individuals.