Your body image: it's more complicated than you think

When he was 19, Ian Waterman suffered a severe bout of viral gastroenteritis that left him with a terrible disability: he lost his sense of proprioception—the ability to sense where his limbs were at any given moment. The sensations from his muscles and joints that would normally alert him to changes in posture and movement simply stopped. Even though his motor functions were still intact, the disease rendered him nearly helpless. 

Ian is now in his sixties and has learned to function pretty well. Still, the only way he knows where his limbs are or what they are doing is to look at them. To control his movements, must consciously command his muscles to contract or relax. If he sneezes, he collapses into a heap. Likewise, if the lights go out when he is standing, he collapses into a heap. For him, without thought, there is no movement. He can never relax.

Can you imagine?! Be glad your proprioception is intact! If all is working well, sensors in your muscles and tendons are constantly supplying information to your brain, which does an amazing job of making sense of it all. For example, your brain compares signals from muscles that are flexing with those that are relaxing. It also constantly monitors the movements of your arms relative to one another, making it possible to align them for tasks. You don’t have to think about all of this like Ian does.

Proprioception enables us to form a kind of central map of our bodies—it’s both a sense of self and body image. Sometimes our brains' processing of sensory input gets out of whack and our body images become disturbed, as is the case with anorexia nervosa, in which people see themselves as overweight; or somatoparaphrenia a condition in which people deny that a part of their body, such as an arm or leg, actually belong to them (they insist on amputation); or phantom limb, where an amputated limb is perceived to continue to exist.

Now I'm going to put my feet up and relax. No problem!

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