Why the 'arm cutting' scene in 127 Hours makes you squirm: Scientists reveal how your brain simulates pain it sees on screen

Whether it's the arm cutting incident in 127 Hours or the fingernail scene in Black Swan, there are plenty of movie moments that make us wince.

Now, experts have revealed why that is the case. 

According to the researchers, our brains simulate the tortuous episodes being played out on screen – making us flinch as if we feel it ourselves.

In their study, they found that parts of the brain thought to be solely linked to vision are also associated with bodily sensations. 

Watching gruesome scenes in TV shows and movies can activate these touch–processing regions in a highly organised way.

In short, the brain doesn't just watch – it simulates what it sees.

'When you watch someone being tickled or getting hurt, areas of the brain that process touch light up in patterns that match the body part involved,' lead author Dr Nicholas Hedger said.

'Your brain maps what you see onto your own body, "simulating" a touch sensation even though nothing physical happened to you.'

The study involved analysing the brain activity of 174 people while they watched a range of films, from Home Alone to Inception. 

Surprisingly, typically 'visual' areas of the brain also contained 'maps' of the body similar to those found in areas associated with processing touch.

In other words, the 'machinery' the brain uses to process touch is 'baked in' to our visual system, the researchers said.

'This cross–talk works in the other direction too,' Dr Hedger said. 

'For example, when you navigate to the bathroom in the dark, touch sensations help your visual system create an internal map of where things are, even with minimal visual input.

'This "filling in" reflects our different senses cooperating to generate a coherent picture of the world.'

Other gruesome movie scenes that regularly make people squirm include the moment in horror franchise Saw when a man decides to saw off his own foot in a bid to escape.

The 1995 thriller Hammer, featuring Robert de Niro, also shows a man being caught cheating and someone taking a hammer to his fingers in punishment.

In the film 127 Hours, a mountain climber is forced to amputate his own arm to free himself after getting trapped.

Meanwhile in Black Swan there is a grisly moment when main character Nina pulls at a hangnail and rips off all the skin down her finger.

The study, published in the journal Nature, reads: 'When seeing others in pain, we may wince, and even remark that we "felt their pain".

'Indeed, when observing others, our brain often responds as if their tactile experience were our own.

'Here, we reveal a widespread mode of brain organisation in which aligned topographic maps bridge vision and somatosensation (sense of touch).'

The researchers said there are several potential clinical applications from their findings.

'This discovery could transform how we understand conditions like autism,' Dr Hedger explained.

'Many theories suggest that internally simulating what we see helps us understand other people's experiences, and these processes may work differently in autistic people.

'Traditional sensory tests are exhausting, especially for children or people with clinical conditions. 

'We can now measure these brain mechanisms while someone simply watches a film, opening up new possibilities for research and diagnosis.'

The study comes shortly after research revealed how scary movies manipulate activity in the brain to boost excitement. 

Finnish scientists mapped neural activity in participants as they watched two horror films – Insidious and The Conjuring 2.

Participants in the study, conducted at the Human Emotion Systems Laboratory in Turku, showed the brain continuously anticipates action in response to threats in two different ways.

Regions of the brain that are involved in visual and auditory perception are triggered during sudden jumpy moments – enabling a rapid evolutionary response to mitigate danger.

Certain regions were also found to be increasingly active during scenes of impending dread as anxiety slowly increased, providing the brain with 'sustained alertness'.

The largest fear response came from the unseen or implied, rather than what they actually saw on the screen.