What Is The Sixth Sense?

Every kid with a little too much interest in the paranormal has spent time locked in their dark bedroom, trying to make the sixth sense real through sheer force of willpower. (Maybe you still do it.) If you were one of those kids, I have good news and bad news. The good news is that a recent study from the National Institutes of Health (NIH) focuses on a sixth sense in humans, establishing a possible genetic cause. The bad news is that this sense has nothing to do with seeing dead people — not that you should let this stop you from trying.

The sense in question is a little thing called proprioception, or the awareness of where our body parts are located in space. Some people are better at it than others; ballet dancers, for example, are intimately aware of their body's position, while someone who's constantly banging their legs on things may not have great proprioception. Last year, researchers at the Scripps Research Institute linked this sense to a specific gene in mice, but it wasn't until recently that scientists have been able to study the relationship between PIEZO2 and proprioception in humans.

So how did they manage that? In an initial study published in the New England Journal of Medicine, NIH researchers performed a series of tests on two patients with a neurological disorder so rare it doesn't have a name. Among other symptoms, they had a problems with balance, a lack of coordination, and difficulty feeling objects touching their skin. Although they could walk almost normally when they could see, both patients staggered and zig-zagged as they walked when they were blindfolded. Similarly, the two patients had trouble reaching for an object in front of their face without looking, and they were less sensitive to certain kinds of touch than people without the disorder. Taken together, researchers suggested that the disorder may cause a lack of proprioception.

Here's where genetics come in: Researchers found that both patients had mutations in the PIEZO2 gene — the same gene that has been linked to proprioception in mice. "The results establish that PIEZO2 is a touch and proprioception gene in humans. Understanding its role in these senses may provide clues to a variety of neurological disorders," said one of the lead authors of the study, Carsten G. Bönnemann, M.D., in a press release.

But that's not the only way the study proved useful. By comparing the abilities of patients with no proprioception to those without the disorder, Bönnemann and fellow investigator Alex Chesler were able to study the role of proprioception in daily life. Patients with the disorder were unable to run or jump, Chesler told NPR, "because those kind of actions really require precise control over your limbs in space."

Fascinatingly, the patients were able to compensate for the lack of proprioception by using their other senses. That's why they were able to walk relatively normally until they were blindfolded; they were able to keep track of their bodies by watching their limbs.

So what does all this mean for you? For one thing, you're probably hyper-aware of your body right now. (Is this what Simone Biles feels like all the time?) For another, Bönnemann suggested to Science that variations of PIEZO2 might at the root of clumsiness. So next time you tumble down a flight of stairs because you misjudged the distance between your foot and the step, you can blame your genes if that makes you feel better.

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