If you were to be presented with a scene of unimaginable gore, where several of your fellow-humans were being hacked to death and their entrails and vital fluids scattered liberally around the room, your immediate reaction would presumably be to run away from this horror, and try to find safety (assuming you weren’t busy vomiting). It would be a bit weird, alarming even, if you were to offer to pay to watch this scenario, possibly while eating popcorn or nachos (which may also lead to vomiting if taken to excess).

And yet, countless people technically do exactly that. The Saw franchise alone has grossed close to a billion dollars at the box office, and that’s just one series of horror films, just at the cinema. There are far more options and formats out there, all dedicated to presenting people with scenes of intense gore and/or fear. And people lap it up (not literally, that would be awful). The point is, there’s clearly a huge market for things which should logically scare or repulse us.

The best example of this is Halloween, which is going on around us right now. A celebration of all the things that should scare us. The fact that it’s warped into an occasion dedicated more to sugar consumption and questionable “sexy” attire is immaterial; we created an occasion to celebrate things that should, by rights, scare us.

“AAAAAH! A child! And the inevitable loss of freedom and crushing weight of responsibility such a thing would bring! RUN!” Photograph: Alamy Stock Photo

But why do people get such a kick out of fear? Looked at one way, it makes no logical sense. Fear is an unpleasant sensation, evolved to make us wary of and able/willing to avoid dangers. This is obviously a vital survival trait, and as such it’s very deeply entrenched in the workings of our brains. Humans are very quick to fear things, and from phobias to social anxieties, even the most seemingly innocuous occurrence can trigger an unpleasant fear reaction. The vomiting reaction to gore also underscores our fundamental disgust response, again a very powerful reaction supported by fundamental brain processes. These things have evolved over millions of years, to keep us safe, healthy and alive. Thus far, they seem to be doing a good job.

Why, then, do the same brains that induce these intensely negative reactions, also motivate us to seek them out? There are a few possible explanations.

At the most basic level, there’s the excitation-transfer theory. Being scared and triggering the fight-or-flight response is incredibly stimulating, having a number of definite effects on our brain’s workings. Excitation-transfer theory argues that the stimulation experienced via fear is essentially transferred to other experiences, which may not be similar in any way. Basically, scary things make everything else more “vivid”, and this is exciting and appealing.

This is quite a simple explanation though, and humans are more complex than that. Another argument is that we all have these dark impulses or “forbidden thinking”, and having some form of outlet for this is a good thing. People regularly wonder about stealing, attacking, cheating, and worse. If you’ve ever stood next to someone by a high drop and thought “What would happen if I just pushed them off?” then you know what this is like. Some argue that indulging in horror and other “video nasties” provides an outlet for this thinking/compulsion, meaning we’re less likely to act on it overall.

Of course, the counterargument is that it desensitises us to such stimulation, meaning we need more intense, visceral entertainment to provoke the same, original reaction. Many people have commented on how modern horror is a far more gruesome, bloodier affair than that from previous decades. Are we seeing desensitisation on a cultural scale?

Ghost, or melting Klansman? Either way, it’s disturbing. Photograph: Andy Crawford/Getty Images/Dorling Kindersley

Another possibility involves the reward pathway. This is the vital region of the brain that produces pleasure and good feeling whenever we do something that the brain fundamentally “approves” of. Drink water when you’re thirsty, eat a high-calorie sweet foodstuff, have an enjoyable sexual encounter with someone you find attractive (or not, up to you), these are things that the brain recognises as positive behaviours, so encourages you to do them again. These things may not be “positive” in the moral or societal sense, we’re talking at a more primitive, physiological level.

Another thing the brain probably considers a positive behaviour is “avoiding death”. When you’re experiencing high levels of fear, the more fundamental brain processes think you’re in danger. Then you’re not scared any more (e.g. because the film ended). Whatever it was you did to escape the scary situation, the brain likes it, so provides a reward. And thus, people experience enjoyment and pleasure from being scared, and happily pay for the privilege by buying films or books that scare us, or join in when everyone runs around scaring everyone else.

Some people take it beyond even this, putting themselves in actual danger by engaging in extreme sports or similar. These people are officially described as having the “sensation seeking” personality trait. More often, they’re labelled “thrill seekers”. There’s even evidence to suggest that such people have genetic properties that compel them to risk their necks, having different expressions of dopamine receptors, which are crucial for the reward pathway.

It only works up to a point, though. And this point is how much control we have of the situation. Even the most dedicated thrill seeker will train and use the best equipment; they don’t randomly hurl themselves off cliffs or out of planes. And the more mainstream horror-lovers may indulge in the most gruesome of entertainments, but they know that at any point they could leave the cinema, stop the DVD, put the book down etc. Actually being in the same room as a vicious serial killer would not be a popular pastime, and genuine beyond-your-control dangers don’t tend to make people happy. They cause things like PTSD.

It seems our brains do enjoy being scared. As long as we can stop it at any time.

Dean Burnett discusses this and many other weird properties of the brain in his book The Idiot Brain, available now in the UK, USA and Canada.