Disgust as a primary emotion

Disgust  is an adaptive system that evolved to motivate disease-avoidance behaviour . It arose in our animal ancestors to facilitate the recognition of objects and situations associated with risk of infection and to drive hygienic behaviour, thus reducing micro- and macro-parasite contact.

From an adaptive stance it has been argued that disgust evolved with the core function of protecting individuals against contamination by facilitating avoidance of toxins and pathogens . In line with this idea disgust has been conceptualised as a disease-avoidance mechanism (Bosman 2016)

Sometime in our evolution towards human ultrasociability, disgust took on an extended role—providing a motive to punish antisocial behaviour and to shun the breakers of social rules (Curtis 2011). 

Individual disgust responses vary according to an individual's personality and learning experience, as well as by local cultural effects such as norms about manners and the symbolism of pollution and purity [7].

Different responses to disgust and fear provoking stimuli

Disgust associated with heart rate deceleration, fear with acceleration 

The results of physiological studies examining heart rate suggests a robust heart rate deceleration for disgust compared to fear, and a moderately consistent heart rate deceleration for disgust compared to neutral stimuli.  .

The finding of slower heart rate for disgust compared to neutral stimuli is important in that it suggests that the heart rate component of the disgust response does not resemble a fear response of smaller magnitude. Instead, the disgust response likely involves a decreased heart rate compared to neutral stimuli, whereas fear involves an increase. The finding of heart rate deceleration for disgust has been theorized to reflect parasympathetic activation (Cisler 2009)

Disgust is associated with anterior insula, fear with amygdala activity in the brain 

Disgust and fear have different facial expressions 

Both fear and disgust are associated with increased corrugator activation, and the observation of increased corrugator activation does not appear able to reliably differentiate fear from disgust. (Cisler 2009).

Disgust stimuli have consistently been shown to be associated with activivation of the levator labii muscle which raises the upper lip, in contrast to fear stimuli which do not result in levator labii activation.

"The observation of levator labii activation  in response to a stimulus, then, seems to indicate the emotion of disgust and not fear. Consequently, it would be predicted that if a stimulus elicits disgust, then levator labii muscle activation is likely to be observed. Additionally, the levator labii is a muscle used in raising the upper lip, which is involved in rejecting food from the mouth and consistent with the evolutionary function of disgust in protecting from disease/contagion." (Curtis 2009).

Disgust and fear are appraised differently

Research and theory on cognitive processes suggest three manners in which disgust and fear differ: 1) disgust involves the law of contagion, 2) disgust involves the law of similarity, and 3) disgust primary appraisals involve beliefs about the object/situation as disgusting, contaminating, or able to elicit the feeling of disgust. Fear appraisals, in contrast, center on estimations of danger/harm.

Disgust, fearfulness and anxiety disorders 

There is increasing evidence implicating disgust in the aetiology and maintenance of various types of anxiety disorders.  In line with this, disgust often complements fear as a common feature of specific phobias such as spider phobia, and a contamination-based obsessive-compulsive disorders (C-OCD) (Bosman 2016)

Exposure therapy is often not effective in reducing disgust

“There is ample evidence that in vivo exposure is highly effective in reducing dysfunctional fears [13]. Although several studies showed that exposure based interventions may also weaken disgust [5], the decline of disgust has typically been shown to be slower than that of fear [14–15]. In other words, it seems that exposure in vivo treatment is less effective in reducing disgust compared to fear.”

 In a similar vein, experimentally conditioned disgust responses (CRs) have also been shown to be relatively insensitive to extinction procedures [16–18]. Specifically it has been found, that although the strength of subjective disgust does show some decline following a series of Conditioned Stimulus (CS)-only presentations, even after an extensive series of extinction trials differential disgust responding to the CS+ vs. CS- typically remains [16, 19]. Based on these types of findings, disgust conditioning has been described as a sticky form of relational learning that is resistant to extinction [20]. “

The relatively strong resistance to extinction might be explained by disgust’s adaptive function to motivate avoidance from contamination threats (pathogens) that cannot be readily detected and are invisible to the naked eye.

Extinction interventions are improved by providing additional safety information (Bosman 2016)

For references please see the original article:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4743916/

Development of disgust 

A study by Outen et al (2010)  presented children with a set of core disgust elicitors which included bad smells, contaminated food, insects and a dirty sock. They showed that children as young as 2.5 years avoided touching these elicitors, but facial expressions of disgust were more frequently seen at a later age. 

Core disgust avoidant behavior was present before children had developed the concepts related to contagion and contamination. 

Bibliography and references 

Bosman, R. C., Borg, C., & de Jong, P. J. (2016). Optimising Extinction of Conditioned Disgust. PLoS ONE, 11(2), e0148626. http://doi.org/10.1371/journal.pone.0148626

Maladaptive disgust responses are tenacious and resistant to exposure-based interventions. In a similar vein, laboratory studies have shown that conditioned disgust is relatively insensitive to Conditioned Stimulus (CS)-only extinction procedures. The relatively strong resistance to extinction might be explained by disgust’s adaptive function to motivate avoidance from contamination threats (pathogens) that cannot be readily detected and are invisible to the naked eye. Therefore, the mere visual presentation of unreinforced disgust eliciting stimuli might not be sufficient to correct a previously acquired threat value of the CS+. Following this, the current study tested whether the efficacy of CS-only exposure can be improved by providing additional safety information about the CS+. For the CSs we included two neutral items a pea soup and a sausage roll, whereas for the Unconditioned Stimulus (US) we used one video clip of a woman vomiting and a neutral one about glass blowing. The additional safety information was conveyed by allowing actual contact with the CS+ or by observing an actress eating the food items representing the CS+. When additional safety information was provided via allowing direct contact with the CS+, there was a relatively strong post-extinction increase in participants’ willingness-to-eat the CS+. This beneficial effect was still evident at one-week follow up. Also self-reported disgust was lower at one-week follow up when additional safety information was provided. The current findings help explain why disgust is relatively insensitive to CS-only extinction procedures, and provide helpful starting points to improve interventions that are aimed to reduce distress in disgust-related psychopathology.

Pitskel, N. B., Bolling, D. Z., Kaiser, M. D., Crowley, M. J., & Pelphrey, K. A. (2011). How grossed out are you? The neural bases of emotion regulation from childhood to adolescence. Developmental Cognitive Neuroscience1(3), 324–337. http://doi.org/10.1016/j.dcn.2011.03.004

The ability to regulate one’s emotions is critical to mental health and well-being, and is impaired in a wide range of psychopathologies, some of which initially manifest in childhood or adolescence. Cognitive reappraisal is a particular approach to emotion regulation frequently utilized in behavioral psychotherapies. Despite a wealth of research on cognitive reappraisal in adults, little is known about the developmental trajectory of brain mechanisms subserving this form of emotion regulation in children. In this functional magnetic resonance imaging study, we asked children and adolescents to up-and down-regulate their response to disgusting images, as the experience of disgust has been linked to anxiety disorders. We demonstrate distinct patterns of brain activation during successful up- and down-regulation of emotion, as well as an inverse correlation between activity in ventromedial prefrontal cortex (vmPFC) and limbic structures during down-regulation, suggestive of a potential regulatory role for vmPFC. Further, we show age-related effects on activity in PFC and amygdala. These findings have important clinical implications for the understanding of cognitive-based therapies in anxiety disorders in childhood and adolescence.

Curtis, V. (2011). Why disgust matters. Philosophical Transactions of the Royal Society B: Biological Sciences, 366(1583), 3478–3490. http://doi.org/10.1098/rstb.2011.0165
Übel S, Leutgeb V, Schienle A. Electrocortical effects of a disgust placebo in children. Biol Psychol. 2015 May;108:78-84. doi: 10.1016/j.biopsycho.2015.03.015. Epub 2015 Mar 28. PubMed PMID: 25829106.

The new synthesis about disgust is that it is a system that evolved to motivate infectious disease avoidance. There are vital practical and intellectual reasons why we need to understand disgust better. Practically, disgust can be harnessed to combat the behavioural causes of infectious and chronic disease such as diarrhoeal disease, pandemic flu and smoking. Disgust is also a source of much human suffering; it plays an underappreciated role in anxieties and phobias such as obsessive compulsive disorder, social phobia and post-traumatic stress syndromes; it is a hidden cost of many occupations such as caring for the sick and dealing with wastes, and self-directed disgust afflicts the lives of many, such as the obese and fistula patients. Disgust is used and abused in society, being both a force for social cohesion and a cause of prejudice and stigmatization of out-groups. This paper argues that a better understanding of disgust, using the new synthesis, offers practical lessons that can enhance human flourishing. Disgust also provides a model system for the study of emotion, one of the most important issues facing the brain and behavioural sciences today.

Übel S, Leutgeb V, Schienle A. Electrocortical effects of a disgust placebo in children. Biol Psychol. 2015 May;108:78-84. doi: 10.1016/j.biopsycho.2015.03.015. Epub 2015 Mar 28. PubMed PMID: 25829106.

The electroencephalogram has been widely used to study voluntary emotion regulation (ER), whereas automatic ER has hardly been investigated. This experiment focused on automatic changes of disgust feelings and event-related potentials due to placebo treatment. Twenty-eight disgust-prone 8- to 13-year-old girls were presented with disgusting, fear-eliciting and neutral pictures once with and once without a placebo (syrup presented with the suggestion that it is able to ease disgust symptoms). In the disgust condition, the placebo reduced experienced disgust and increased frontal late positivity (400-1000 ms after picture onset). A similar electrocortical placebo effect was obtained for the fear pictures. These findings suggest that the placebo had the function of a safety signal which helped the children to direct their automatic attention to the aversive stimuli and to overcome visual avoidance. Future studies should integrate behavioral designs and should use additional psychophysiological measures (e.g., eye-tracking) in order to substantiate this interpretation.

Schienle, A., Übel, S., Schöngaßner, F., Ille, R., & Scharmüller, W. (2014). Disgust regulation via placebo: an fMRI study. Social Cognitive and Affective Neuroscience, 9(7), 985–990. http://doi.org/10.1093/scan/nst072

​The present fMRI study investigated whether placebo treatment can change disgust feelings.Disgust-prone women underwent a retest design where they were presented with disgusting, fear-eliciting and neutral pictures once with and once without a placebo (inert pill presented with the suggestion that it can reduce disgust symptoms). The placebo provoked a strong decrease of experienced disgust, which was accompanied by reduced insula activation. Exploratory psychophysiological interaction analyses revealed decreased connectivity in a network consisting of the insula, the amygdala, the anterior cingulate cortex and the orbitofrontal cortex. Moreover, the placebo increased amygdala-DMPFC coactivation. Our findings suggest that placebo use can modulate a specific affective state and might be an option as a first therapy step for clinical samples characterized by excessive and difficult-to-control disgust feelings.

Stevenson RJ, Oaten MJ, Case TI, Repacholi BM, Wagland P. Children's response to adult disgust elicitors: development and acquisition. Dev Psychol. 2010 Jan;46(1):165-77. doi: 10.1037/a0016692. PubMed PMID: 20053015.

Little is known about when or how different disgust elicitors are acquired. In Study 1, parents of children (0-18 years old) rated how their child would react to 22 disgust elicitors. Different developmental patterns were identified for core, animal, and sociomoral elicitors, with core elicitors emerging first. In Study 2, children (2-16 years old) were exposed alone and then with their parent to a range of elicitors derived from Study 1. Self-report, behavioral, and facial expression data were obtained along with measures of contagion, conservation, and contamination. Convergent evidence supported the developmental patterns reported in Study 1. Evidence for parent-child transmission was also observed, with parents of young children emoting more disgust to their offspring and showing greater behavioral avoidance. Moreover, child reactivity to animal and sociomoral elicitors and contamination correlated with parental responsiveness. Finally, young children who failed to demonstrate contagion and conservation knowledge were as reactive to core elicitors and contamination as children of the same age who demonstrated such knowledge. These findings are interpreted within an evolutionary framework in which core disgust responses are acquired early to promote avoidance of pathogens.