Sana, Sawsen, and a handful of similar patients are ideal subjects for scientists who study touch and proprioception. It’s also given us a more complete understanding of what it means to be human and experience the world through a body. That has led to hopeful insights that could yield better ways to treat pain and better prostheses for amputees. But in the past decade, neuroscientists have made huge breakthroughs that reveal how touch and proprioception work. Of all the senses, touch and proprioception are arguably the least understood. “Even with my eyes open, when I touch the little ball, I don’t feel it,” Sawsen says. The sisters, whose last names I’m not using for privacy reasons, also share another curiosity: They can’t feel a lot of the things they touch. The first few seconds, you don’t know what direction you’re going in.” Pure disorientation.
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“It’s as if you had a blindfold and somebody turned you several times, and then you’re asked to go in a direction. “At home,” Sawsen says, if the power goes out and she’s standing up, “I fall to the ground.” The feeling is as hard to imagine as it is to describe. She, too, has trouble finding her nose in the dark. Another is her older sister, Sawsen, 36, who was also undergoing the testing at the NIH, in August. Sana is one of the few people in the entire world who knows what it’s like when the proprioceptive sense is turned off. We know what silence is when we cover our ears, we know what darkness is when we shut our eyes. Proprioception is different from the others in a key way: It never turns off, except in very rare cases. Scientists sometimes refer to it as our “sixth sense.” And like the other senses - vision, hearing, and so on - it helps our brains navigate the world. This sense is called proprioception (pronounced “pro-pree-o-ception”) it’s an awareness of where our limbs are and how our bodies are positioned in space. When we close our eyes, our sense of the world and our body’s place in it doesn’t disappear. Then try to find it with your eyes closed. Touch the top of it a few times with your eyes open. When her eyes are closed, she doesn’t know where her body is in space. “It’s like I am lost,” she says, through an interpreter. She struggles to find her nose on her face, outright missing a few times. When she manages to touch the ball, it seems like an accident. She gropes around, swinging her arm widely to the left and the right.
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Suddenly, it’s like the location of the ball has been erased from her mind. He lets go and asks Sana to do it herself while keeping her eyes closed. He places her finger on the ball, and then moves it back to her nose. She touches the ball.Ī lab technician tells her to close her eyes. Here’s the challenge: She’s asked to touch her nose and then touch the ball in front of her. On the desk, a black cylinder stands upright. Surrounding her, 12 infrared cameras tracking her every move. Sana, a petite 31-year-old French woman with curly brown hair, is strapped to a chair at the Clinical Center at the National Institutes of Health.