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- Sarolidou, Georgia
(författare)
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A behavioral defense against disease
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Animals, including humans, have evolved under the continuous selection pressure posed by pathogens. As a result, we have developed a set of physiological mechanisms to combat pathogens – the immune system. However, engaging the immune system in this battle can be costly, unnecessarily so in cases when pathogens can be avoided. Recent studies have focused on the behavioral defense against disease, which helps us to avoid pathogens before they enter the body by detecting and avoiding sources of contagion. A behavioral defense can also be argued to promote recovery if infected, through so-called sickness behavior. Both aspects are related to motivational states that help the organism reorganize its priorities to promote disease avoidance and recovery. In this thesis, we investigated by which perceptual cues, facial and/or olfactory, humans are able to dissociate between sick and healthy individuals as well as how these cues can affect social liking of other people. We also investigated whether sick individuals would exhibit sickness behavior that includes relevant shifts in chemosensory perception of food and social odors. In Study I, we investigated whether facial expressions of emotion change during sickness. Twenty-two healthy volunteers were injected with either an endotoxin (lipopolysaccharide, LPS; 2ng/kg body weight) or saline. Facial photographs of the volunteers were taken 2 hours after the injections. At a later stage, 49 naïve participants were asked to rate the emotional expressions and the perceived health of both the sick and healthy faces. The results showed that sickness had a negative effect on facial expressions of emotion. Sick faces looked significantly more sad and disgusted, as well as less happy, compared to the healthy faces. Moreover, the emotional expressions mediated 59.1% of the treatment-dependent changes in ratings of the perceived health of the faces. In Study II, using the sick and healthy facial photographs from Study I and body odors from the same volunteers, we investigated the effects of olfactory and facial (visual) disease cues on social liking. We also assessed whether individual traits such as perceived vulnerability to disease, disgust sensitivity, and health anxiety could influence participants’ liking ratings. Seventy-seven participants were presented with sick and healthy facial photographs and body odors in a 2 x 2 factorial design. During the presentation of the stimuli, facial electromyographic activity was recorded as an objective measure of participants’ own facial expressions of emotion. The results revealed a negative main effect of both facial and body odor sickness cues on liking ratings, indicating that sick individuals are liked less than their healthy counterparts. No significant effect of sickness cues on facial electromyographic activity was found. Finally, we showed that participants who perceived themselves as more vulnerable to disease liked the presented volunteers less [than other participants did], regardless of health status. In Study III, we sought to examine if, apart from experimentally induced inflammation, naturally occurring inflammation can result in an altered body odor. As in Study II, the effect of individual traits – perceived vulnerability to disease, disgust sensitivity, and health anxiety – on sickness perception was also assessed. Body odors were collected from 23 volunteers who were experiencing respiratory infections. Three weeks later, body odors from the same individuals were collected again, after they had recovered. In a later stage, 46 participants rated the body odors in terms of intensity, disgust, pleasantness, and health. Our results showed that the sick body odors, in line with hypotheses, smelled nominally more intense, more disgusting, and less healthy compared to the healthy body odors, though these results did not reach statistical significance. Moreover, there was no association between the individual traits and body odor perception. In Study IV, we assessed the effect of sickness on odor and taste perception. Relevant to this study is the fact that sickness behavior entails both a loss of appetite and social withdrawal. Using an experimental disease model, 40 participants received LPS (between 0.51 and 0.80 ng/kg body weight) or saline injections. They were then presented with eight different odors (two food odors, three social odors, and three control odors) and four different basic tastes (plus a control) and asked to rate the intensity and pleasantness of these stimuli. In line with the hypothesis, participants perceived food odors as significantly less pleasant when they were sick. No significant effect of sickness on ratings of social odors, control odors, or tastes was found. In conclusion, the present thesis reveals a number of perceptual sickness cues with the potential to trigger avoidance or limit approach behavior. These cues are available as early as a few hours after the induction of systemic inflammation. Once sick, an individual demonstrates less motivation to consume food, as indicated by a dampened perception of food odor pleasantness, likely in favor of allocating resources to recovery. Avoiding the sickness cues and engaging in the sickness behaviors identified in this thesis may be important in a behavioral defense against disease that helps us stay alive and healthy.
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| 2. |
- Sarolidou, Georgia, et al.
(författare)
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Disease detection : Volatile biomarkers in acute inflammation
- 2017
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Ingår i: Chemical Senses. - : Oxford University Press (OUP). - 0379-864X .- 1464-3553. ; 42:2
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Tidskriftsartikel (refereegranskat)abstract
- Through history, infectious bacteria and viruses have posed a threat to humanity. Being able to detect and avoid pathogens is, therefore, of crucial importance. It has been shown that body odor samples, such as urine, from immune-activated animals contain sickness cues and detection of which, results in avoidance behavior in conspecifics. Perceivable changes in body odor samples have also, recently, been shown in immune-activated human participants. The main aim of this study was to identify potential volatile biomarkers of the acute inflammatory response. Healthy volunteers were injected twice in a crossover design, once with the bacterial endotoxin lipopolysaccharide (LPS, 2ng/kg bw) and once with placebo (saline). LPS caused a transient systemic inflammatory response as shown by pro-inflammatory cytocines, tympanic temperature and subjective sickness ratings (significant interactions between condition and time with all ps<.001, and all ηρ2>.663). Axillary sweat and urine were collected both before and 2–4 hours after injection. Headspace from these samples were analyzed using gas chromatography-mass spectrometry (GC-MS). GC-MS data analyses assessed the differences in the profile of volatile compounds of urine and sweat from LPS and placebo donors. Results regarding possible differences between volatile biomarkers in LPS and placebo condition will be presented and discussed.
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| 3. |
- Sarolidou, Georgia, et al.
(författare)
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Emotional expressions of the sick face
- 2019
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Ingår i: Brain, behavior, and immunity. - : Elsevier BV. - 0889-1591 .- 1090-2139. ; 80, s. 286-291
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Tidskriftsartikel (refereegranskat)abstract
- To handle the substantial threat posed by infectious diseases, behaviors that promote avoidance of contagion are crucial. Based on the fact that sickness depresses mood and that emotional expressions reveal inner states of individuals to others, which in turn affect approach/avoidance behaviors, we hypothesized that facial expressions of emotion may play a role in sickness detection. Using an experimental model of sickness, 22 volunteers were intravenously injected with either endotoxin (lipopolysaccharide; 2 ng/kg body weight) and placebo using a randomized cross-over design. The volunteers were two hours later asked to keep a relaxed expression on their face while their facial photograph was taken. To assess the emotional expression of the sick face, 49 participants were recruited and were asked to rate the emotional expression of the facial photographs of the volunteers when sick and when healthy. Our results indicate that the emotional expression of faces changed two hours after being made temporarily sick by an endotoxin injection. Sick faces were perceived as more sick/less healthy, but also as expressing more negative emotions, such as sadness and disgust, and less happiness and surprise. The emotional expressions mediated 59.1% of the treatment-dependent change in rated health. The inclusion of physical features associated with emotional expressions to the mediation analysis supported these results. We conclude that emotional expressions may contribute to detection and avoidance of infectious individuals and thereby be part of a behavioral defense against disease.
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| 4. |
- Sarolidou, Georgia, et al.
(författare)
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Olfactory Communication of Sickness Cues in Respiratory Infection
- 2020
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Ingår i: Frontiers in Psychology. - : Frontiers Media SA. - 1664-1078. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Animals detect sick conspecifics by way of body odor that enables the receiver to avoid potential infectious transmission. Human observational studies also indicate that different types of disease are associated with more or less aversive smells. In addition, body odors from otherwise healthy human individuals smell more aversive as a function of experimentally induced systemic inflammation. To investigate if naturally occurring immune activation also gives rise to perceivable olfactory changes, we collected body odor samples during two nights from individuals with a respiratory infection as well as when they were healthy. We hypothesized that independent raters would rate the body odor originating from sick individuals as smelling more aversive than when the same individuals were healthy. Even though body odor samples from sick individuals nominally smelled more intense, more disgusting, and less pleasant and healthy than the body odor from the same individuals when healthy, these effects were not statistically significant. Moreover, raters filled out three questionnaires, Perceived Vulnerability to Disease, Disgust Scale, and Health Anxiety, to assess potential associations between sickness-related personality traits and body odor perception. No such association was found. Since experimentally induced inflammation have made body odors more aversive in previous studies, we discuss whether this difference between studies is due to the level of sickness or to the type of trigger of the sickness response.
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| 5. |
- Sarolidou, Georgia, et al.
(författare)
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People expressing olfactory and visual cues of disease are less liked
- 2020
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 375:1800
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Tidskriftsartikel (refereegranskat)abstract
- For humans, like other social animals, behaviour acts as a first line of defence against pathogens. A key component is the ability to detect subtle perceptual cues of sick conspecifics. The present study assessed the effects of endotoxin-induced olfactory and visual sickness cues on liking, as well as potential involved mechanisms. Seventy-seven participants were exposed to sick and healthy facial pictures and body odours from the same individual in a 2 x 2 factorial design while disgust-related facial electromyography (EMG) was recorded. Following exposure, participants rated their liking of the person presented. In another session, participants also answered questionnaires on perceived vulnerability to disease, disgust sensitivity and health anxiety. Lower ratings of liking were linked to both facial and body odour disease cues as main effects. Disgust, as measured by EMG, did not seem to be the mediating mechanism, but participants who perceived themselves as more prone to disgust, and as more vulnerable to disease, liked presented persons less irrespectively of their health status. Concluding, olfactory and visual sickness cues that appear already a few hours after the experimental induction of systemic inflammation have implications for human sociality and may as such be a part of a behavioural defence against disease. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.
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| 6. |
- Tognetti, Arnaud, et al.
(författare)
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Acute Systemic Experimental Inflammation Does Not Reduce Human Odor Identification Performance
- 2021
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Ingår i: Chemical Senses. - : Oxford University Press (OUP). - 0379-864X .- 1464-3553. ; 46
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Tidskriftsartikel (refereegranskat)abstract
- Olfactory dysfunction is a common symptom of various diseases, but the underlying pathophysiology has not been fully understood. Evidence from both animal and human studies suggests that local inflammation of the olfactory epithelium is linked to olfactory dysfunction. However, whether systemic inflammation causes olfactory dysfunction is yet to be determined. In the present behavioral study, we set out to test whether acute systemic inflammation impairs olfactory identification performance by inducing a transient and controlled state of systemic inflammation using an experimental endotoxemia model. We treated young healthy participants (N = 20) with a relatively high dose (2.0 ng/kg) of lipopolysaccharide (LPS) and a placebo treatment in a double-blind within-subject design, and assessed participants' ability to identify odors using the MONEX-40, a reliable method for experimental assessment of odor identification ability in healthy and young individuals. Our results show that olfactory identification performance was not affected by the acute systemic inflammation triggered by the injection of LPS. Moreover, odor identification performance following the LPS injection was not associated with levels of circulating proinflammatory cytokines (interleukin-6, interleukin-8, and tumor necrosis factor-alpha). Because experimental LPS-induced systemic inflammation does not affect olfactory identification performance, our findings suggest that chronic, rather than transient, systemic inflammation is a more likely mechanism to explore in order to explain the olfactory deficits observed in inflammatory diseases.
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