New findings show how visual scenes trigger touch echoes in the brain

New findings show how visual scenes trigger touch echoes in the brain

Watching Robert De Niro order hammer-based retaliation on a cheater's handcasinomade you instinctively cringe, you're not alone. Many people say that when they see physical assault on film, they cringe as if they themselves “feel” it. It's like the stinger jumps straight from the screen into your skin.

But the explanation of why and how this happens has long puzzled scientists. Now scientists from the University of Reading, the Free University of Amsterdam and Minnesota, USA, have found an important clue to the cause. Parts of the brain originally thought to process only vision are also organized according to a “map” of the body, so that what we see triggers echoes of touch sensations.

The study was published today (Wednesday, November 26) in the journalNatureshows that watching movies can activate touch-processing regions of your own brain in a highly organized way. In short, your brain doesn't just watch, it simulates what it sees.

When you watch someone being tickled or hurt, areas of the brain that process touch light up in patterns that correspond to the part of the body affected. Your brain transfers what you see to your own body, “simulating” a sensation of touch even if nothing physical has happened to you.

This crosstalk also works in the other direction. For example, when navigating to the toilet 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 the interaction of our various senses to produce a coherent picture of the world.”

Dr. Nicholas Hedger, lead author from the Center for Integrative Neuroscience and Neurodynamics at the University of Reading

Body maps hidden in the visual system

To show how it is possible that our sense of touch is activated solely by visual information, researchers developed novel methods to analyze the brain activity of 174 people while they watched films such as "The Social Network" and "Inception." Surprisingly, brain regions traditionally thought to process purely visual information showed patterns that reflected sensations about the viewer's own body, not just what appeared on the screen. These visual regions contained “maps” of the body, similar to those normally found in touch-processing areas of the brain. In other words, the “machinery” that the brain uses to process touch is “baked into” our visual system.

The study found two ways these body maps correlate with visual information. In the dorsal (higher) regions of the visual system, the body maps match where things appear in our field of vision: parts of the brain tuned to foot sensations were also tuned to the lower parts of the visual scene, while parts tuned to facial sensations were also tuned to the upper parts of the visual scene. In ventral (further down) regions, body maps match the part of the body someone is looking at, regardless of where it appears in the visual scene. To put it simply, our visual system is closely linked to our sense of touch and maps what we observe to the coordinates of our body.

The researchers are particularly excited about the clinical applications of this research. Hedger said: “This discovery could transform our understanding of disorders such as autism.”

Many theories suggest that internal simulation of what we see helps us understand other people's experiences, and that these processes may work differently in autistic people. Traditional sensory testing is stressful, especially for children or people with clinical illnesses. We can now measure these brain mechanisms while someone simply watches a movie, opening up new opportunities for research and diagnosis.”

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