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The Insular Cortex - our disgust center


Have you ever eaten food that smelled or tasted rotten or rancid? What happens? You start producing more saliva. Your throat muscles start contracting. You start gagging and you might vomit the food out. 

This happens because a part of your brain - the insular cortex, activates, and protects you from eating food which is potentially harmful. It's a way your brain has evolved to protect you. 


But here’s where you can set a test for yourself. Imagine now eating something disgusting, say a large cockroach. Imagine its feelers curling up in your mouth, and its feet scrambling against your lips, and as you bite into it, bile and innards explode out onto your tongue and teeth. Does your stomach feel queasy? A bad taste in your mouth?


Let’s go a bit further. Forget about eating or imagined eating. Let’s think of something that is morally repulsive to you. Maybe it’s sexually abusing a toddler. Or your race enslaved by another simply because of skin colour. Someone wealthy throwing money at a poor person, after injuring him in a car accident. For the religious, homosexuality. For the atheists, childhood religious indoctrination. 

Do you feel queasy? Sick to the stomach? Bad taste to the mouth? If you're put in a brain scanner, guess which part of your brain activates when you see something morally repulsive? Yes, it’s the insular cortex.

The part of your brain that processes gustatory disgust is the same as the part that processes moral disgust.


Note the similarities in the language we use to describe both gustatory and moral disgust.  Sick to your stomach. Makes me queasy. Bad taste in your mouth. Makes me want to vomit. Think of the equivalent in other languages (for mandarin: 反胃,恶心,想吐). I can’t speak most languages but I can assure you that gustatory and moral disgust must be described in similar ways. Our biology affects our behaviour, which in turn shaped our language. And all this happens without us being consciously aware.

How the insular cortex activates is an important point. This vivid and visceral emotion and sensation that triggers upon moral disgust enable what was cognitive and mental to become something real and physical. It is literally that disgust you taste in your mouth that compels you to take action, and stand up against it. 

However, this strong reaction is a double-edged sword. It empowers us to take action on what is disgusting. But there is no universal standard of disgust. What is morally disgusting to one person might be perfectly normal to another. And we have a tendency something that we are not doing to be disgusting, even if it is part of another person's daily life.

When disgust is triggered, your insular flashes a warning sign to your amygdala  - look at how disgusting this person is making me feel, this person must be horrible and absolutely wrong. Because your judgement of this person is tied to such a strong and distressing biological and emotional response,  you develop an amplified negative image of the offending person; you internally criminalise him/her.  


This explains why there is such deep hatred and animosity between certain groups. One person who is homosexual and one who is staunchly religious might have very similar careers and very similar views on most things. But because homosexuality/rejection of homosexuality is so polarising, the insular cortex activates, brandishing the other view as being disgusting and completely unacceptable.

Another example. One race might view another as being so repulsive they no longer see them as human. This was a tragedy that happened in the Rwandan civil war between the Hutus and Tutsis, leading to Hutu leaders like Leon Mugesera to brandish the Tutsis as cockroaches. Mugesera's insular cortex would have activated so much that he simply said what he felt. When combined with the amygdala, it leads us to readily develop a "Us vs Them" mentality. You can think of many other examples. Food consumption. Living habits. Political views.  

Just like all other emotions, disgust happens to us subconsciously. What this means is that we might not even know how much our emotions have coloured our thinking.

  • A strong feeling of disgust is triggered in your insular cortex. 

  • Insular cortex syncs with your amygdala; you start developing anger and aggression and fear of the other party

  • Your amygdala, in turn, has strong and direct neural links with your pre-frontal cortex. You might start developing cognitive justifications for why you have disgusted and angry.

  • In other words, the strong influence of your emotions causes you to explain something in a certain manner, when if you were in a calm state, you might have seen and explained the same thing completely differently. 

This is another reason why we have to look at each behaviour and each thought holistically, rather than trying to explain it from a single source.

Fun fact:

The development of the insular cortex from one that just dealt with gustatory disgust to the current version that deals with both gustatory and moral disgust shows the wonders of evolution. While humans have been around for about 100,000 years, social norms (and the extreme violation of these norms causing moral disgust) only developed 40000-50000years ago. This happened when groups of humans started living together, and norms were the rules by which these groups developed to guide co-existence. Your brain didn’t grow a new part to deal with this new development. You simply evolved, and in such a beautiful, efficient way, where the insular cortex expanded to perform 2 related roles. 

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