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Why do you retch when you see something disgusting?

I imagine it is some sort of evolutionary response, although I can't see the connection between receiving a signal that unhealthy conditions are in the current environment and wanting to empty the contents of one's stomach, which likely were eaten elsewhere. The response I would have expected to have developed would have been one of fleeing, rather than vomiting.

As a subquestion, why does the same reaction sometimes occur when imagining something disgusting, even if it is not real?

(I know "disgusting" is subjective; I'm referring to things humans may want to not be around for health reasons, e.g. rotting flesh, infestations of traditionally disease-carrying insects, etc.)

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    $\begingroup$ I wonder if this question isn't more appropriate on CogSci SE, as not all people are effected in this way, and there may be more of a psychosocial aspect to it than one that is strictly biological. $\endgroup$
    – AMR
    Dec 16 '15 at 21:58
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    $\begingroup$ @AMR That's a good point. I'm going to give it a bit more time to marinate here to see what comes of it before moving it. $\endgroup$
    – Jason C
    Dec 16 '15 at 22:11
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    $\begingroup$ I am not very familiar with neurology, but I know that people can have sensitivities to things like blood draws etc. because of vasovagal response. Some may be more highly sensitive than others. $\endgroup$
    – AMR
    Dec 16 '15 at 22:15
  • $\begingroup$ Seems to me your body telling you to stay away from something rather than it just being unpleasant to to look at is, is a stronger more reinforced manner of personal protection/preservation. Interesting ? Though curious to see what else era posted. I think it's fine here on bio SE By the way $\endgroup$
    – rhill45
    Dec 17 '15 at 1:39
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Physiologically speaking, your body is reacting to something you have known associations learning. An extreme form of this phenomenon is seen in drug addiction. After chronic use of a substance there are certain cues a person associates with the drug effects. Whether that be a certain group of people, a sound, a place, or an object the stimulant is eventually associated with the drug effect. After a certain amount of time a physiological reaction occurs with just the introduction to the stimulant without the drug. Often, if an addict receives a stimulation without a drug they are, at first, excited, calm, or feeling whatever the drug effects caused. But then, if no drug is received, the withdrawal effects come into play and makes the addict feel worse and crave the drug more intensely.

Anyway, so when you see something you associate with being gross or awful, your bodies physical reaction is essentially prepping you for the event.The biological and cellular effects of associative learning are regulated in the central nervous system (brain). The main theory is that the initial effect of the stimulus is regulated by dopaminergic channels, and the learning and associations are regulated by serotonergic channels. However, it is more like a complex network of synaptic channels at work in various parts of the brain. The regions known to be apart of associative learning are the emotional cortex of the brain are the amygdala, prefrontal cortex, and hippocampus.

For gastrointestinal upset the stimulus is most likely associated with an event that caused GI upset previously. For example, let's say you went out to a party and had too much to drink. You throw up everything you've eaten that day and you just generally feel awful and 'sick to your stomach.' Now, every time you see, smell, or taste that brand or flavor of alcohol you consumed, you immediately gag because your body is remembering the previous event and associates that stimulus with the vomiting and sick feeling. Does that make sense? Let me know if you would like more clarification.

Sources:

  1. Drug Addiction Drug Habituation - Profiles in Science
  2. Control of cocaine-seeking behavior by drug-associated stimuli in rats: Effects on recovery of extinguished operant-responding and extracellular dopamine levels in amygdala and nucleus accumbens
  3. Neural and psychological mechanisms underlying appetitive learning: links to drug addiction
  4. Physcopharmacology by: Meyer and Quenzer (ISBN 978-0-87893-510-9) (best source)
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  • $\begingroup$ That sort of makes sense, except why vomiting / gagging? Not only are there other conceivable reactions to disgust (for example why not experience a sudden urge to wash one's self rather than purge stomach contents), but there are other conceivable reactions in general (for example, fear instead of disgust, that is an urge to flee rather than purge). Or, in other words, when you say "prepping you for the event", what event is being prepared for and why is vomiting preparation for it? $\endgroup$
    – Jason C
    Dec 17 '15 at 14:02
  • $\begingroup$ The association is usually something gastrointestinal based if you are gagging. Aka. usually the event associated with the stimulus is related to gastrointestinal upset, like eating bad food one time, or throwing up after drinking too much. I'll try to add that to my answer :) $\endgroup$
    – ephackett
    Dec 17 '15 at 14:05
  • $\begingroup$ So, the claim is, it's not an evolutionary response, but rather the remains of a learned response, specifically related to eating and now sometimes applied inappropriately, to stimuli encountered previously? $\endgroup$
    – Jason C
    Dec 17 '15 at 14:18
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    $\begingroup$ Essentially. It could be evolutionary, but it would be extremely difficult to prove and the less logical of the concepts. You would have to have a gag reflexes to stimuli you have never seen or have associations with, which most people don't. It is also pretty much impossible to research because babies are getting sensory overload and making learning associating from the second they are born, and we can't look at the animal lineage because there is no way to detect a gag in an animal. $\endgroup$
    – ephackett
    Dec 17 '15 at 14:25
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    $\begingroup$ I wonder if there is any studied and documented correlation between people who are more prone to having this response (such as those who gag at the site of blood) and some sort of specific eating-related events during childhood. I'm going to pursue that and see if I can find anything. I am also becoming more convinced that this may be a CogSci topic. $\endgroup$
    – Jason C
    Dec 17 '15 at 14:31

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