Primal fear is basic.Fear is fed on the simplest, sparest diet and grows fat in the brain fast, making you sweat and go weak in the knees. This is why the horror video game's toolbox is also simple. From modern chillers like Amnesia: The Dark Descent , to classics like Silent Hill, and all the way back to primordial horror games like the Atari 2600's Haunted House, the horror game designer frightens you with the same trade tricks: darkness, discordant noise, dysmorphic imagery, and ignorance. Great horror games are scary because they take away your senses and leave you unsure of anything. Killer graphics, art direction, and gripping combat aren't the most powerful tools at the horror designer's disposal; your body is.

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“ When we become frightened our sympathetic nervous system takes over as we ready for 'fight or flight.'

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“ As we get scared, our body stops everything else it's doing and focuses purely on self-preservation.

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“ Like a drug, we build fear tolerance.

Take Fatal Frame II, the PlayStation 2's premier ghost story, as a prime example of how a video game manipulates the senses into a frothy state of high anxiety. Leading lead character Mio through an abandoned mountain village is harrying even when you know there's ghosts everywhere waiting to drag you to hell. Director Keisuke Kikuchi plays the player by steeping scene in darkness, limiting your visual range to what you can see in the beam of a flashlight. The game constrains your peripheral vision even further--in first person you can only see what's directly ahead, and in third person the action is presented for extreme camera angles (which has the added effect of making you feel watched by an unseen force.)Mio moves slowly. Even when there's no music, the game plays a low frequency tone to aurally lull the player into anticipating something. All of these constraints put together make you dread going into new rooms and freak out when the ghost of some dead priestess inevitable appears, even when you're expecting her. And you love it when it happens."This state involves an adrenaline rush and ancillary activation of dopamine and endorphin. This flood of neurotransmitters is accompanied by elevations in heart rate, respiration, blood pressure, and blood sugar, along with pupil dilation and narrowed attention. The fear response is grounded in evolution. Whether fighting or fleeing, the adrenaline rush readies our minds and bodies to react to perceived threats with greater strength and speed than they could in our every day resting state."As we get scared, our body stops everything else it's doing and focuses purely on self-preservation. Horror games take full advantage of that by toying with and teasing the senses, scaring you and then providing momentary relief. "One theory holds that there's an adrenaline rush carryover that intensifies our emotional experiences even after a fearful scene has subsided, though we're not aware of it," said Donner, "So there's something of an electrified effect in the aftermath of a scare that may be appealing."The other reason we're drawn to games that make us terribly uncomfortable and afraid is that they provide a distinct psychological fantasy rather than an aspirational one. Many games make you a hero, and while horror games often do as well, what your brain really likes is how unfamiliar their scenarios are. "The novelty of fearful circumstances makes them alluring--it allows for a break from our everyday routines and keeps our systems practiced, said Donner, "Distraction from everyday problems also appears to drive fear-enjoyment; when our minds are focused on a slasher scene for example, bills and work problems are temporarily banished."Truly frightening horror games that keep delivering the fear drug are rare, though. By their very nature, video games are repetitive. If you're playing a horror game like Resident Evil, there's a possibility that the famous dog jumping through the window will actually kill STARS agent Chris Redfield. When you reload your saved game, the dog won't scare you that second time. The brain braces for that moment, and the rest of the body follows suit. Like a drug, we build fear tolerance.It's an exciting moment for horror games; because of newer tools give designers even more access to the player's body. Oculus Rift, for example, can transform first-person horror games into more physical experiences by incorporating the player's natural field of view. Just imagine glimpsing one of Amnesia's blurry freaks chasing you down inside a VR helmet to get an idea of the potential. New tech won't lead to a revolution in horror game making, though. No horror game director can change the human body. Then again, when it's so effective at making horror work, why would they want to?

Anthony Agnello is a freelance writer. He owns two beaches and likes long walks on cats. He can be followed on Twitter at @ajohnagnello