While walking, sensor receptors on your skin, joints and muscles send signals to the brain that make you aware that your right foot is in front of you even if your eyes are closed or you’re not looking down at your feet, 

What if you lost all sense of self? You know you have a body — you can see it there beneath you, but you can’t feel it. You aren’t paralyzed, per se, just unaware that your body is moving unless you are looking at it. And then, only under intense concentration and your own watchful eye, can you reach out toward something and grasp it. But if you don’t look or pay close attention, the object will either slip out of your hand because you are holding it too loosely, or you’ll squeeze it with such intensity your knuckles will turn bone white.

This ability to feel our bodies, to unconsciously sense them is known as proprioception. It’s sometimes referred to as the secret sense — or “sixth sense.” Unlike our five senses — sight, sound, smell, touch and taste — which are open and obvious to us, the sense of controlling and owning our own bodies is otherwise hidden. We are usually unaware of this sensation … unless something goes wrong.

What Is Proprioception?

Proprioception is, simply put, the awareness of where your body is in space. For example, while walking, sensor receptors on your skin, joints and muscles send signals to the brain that make you aware that your right foot is in front of you even if your eyes are closed or you’re not looking down at your feet, explains Dr. Jack Shelley-Tremblay, professor and chair of the department of psychology at the University of South Alabama.

Proprioception is sometimes used interchangeably with the term “kinesthesia,” but they are actually very different perceptions. Kinesthesia is the sense of movement of our muscles, tendons and joints.

For example, while walking, the brain picks up on the sensations of force, velocity and the propelling of your body forward from the inner ear, which oversees balance orientation, to sense movement. You are aware of the sensation of your body being in motion even if you are focused on the scenery around you and not your body.

Proprioception and kinesthesia, while different, work together to make us cognizant of our own bodies in space. Combined, they can be considered the sixth sense or, respectively, as the sixth and seventh senses.

You are aware of the sensation of your body being in motion even if you are focused on the scenery around you and not your body  

Can Proprioception Go Awry?

Proprioception plays a vital role in balance and orientation, enabling us to stand upright or walk, especially on uneven surfaces. It allows golfers to perfect their swings and dancers to move with the grace of a butterfly. “When it functions normally, we take it for granted,” Shelley-Tremblay says. But, “one of the most fascinating things about proprioception is when it fails.”

Sometimes people feel a temporary impairment of this sixth sense. Think of someone who’s intoxicated taking a field sobriety test, for instance. With their vestibular system impaired by too much alcohol, they have a sense of proprioception loss and thus have a difficult time walking in a straight line or balancing on one foot. A more precise example is when your arm falls asleep and, as a result, it feels numb and is difficult to move.

Sometimes injuries or disorders can cause a permanent loss of proprioception:

• Brain injuries
• Arthritis
• Stroke
• Peripheral neuropathy
• ALS (Lou Gehrig’s disease)
• Parkinson’s disease

People with a proprioception disorder or impairment may experience, at times, one or more of the following symptoms:

• Sensation of being off balance
• Incoordination or clumsiness
• Prone to falls
• Unable to recognize their own strength, such as pressing down too hard with a pencil when writing

Proprioception-related Syndromes

There are two unusual conditions that are related to proprioception:

• Alien limb syndrome: Also called alien hand syndrome, this neurological disorder can affect the hand or the leg and causes the limb to acts independent — or involuntarily — of the person’s desires. British neurologist Oliver Sacks describes in a chapter of his book “The Man Who Mistook His Wife for a Hat” a patient who woke to find what he believed to be a cadaver’s left leg in bed with him. Disgusted, the man pushed the leg off the bed only to drop onto the floor after it. He then became distraught when he realized the strange leg was attached to him.
• Phantom limb syndrome: A condition that can affect amputees, phantom limb syndrome occurs when someone feels sensations in the limb that has been removed. For some, it can be a painful experience. One man describes the sensation in his phantom hand as being a constant state of tight clenching that neither painkillers or hypnosis could ease. Neuroscientist Vilayanur S. Ramachandran suggests the signals going from his muscles to his brain are not getting the feedback to stop clenching because the eyes are not seeing the hand. Ramachandran successfully shows that by placing the man’s intact arm in a mirror box, the man could “visually resurrect the phantom limb” and convince his brain to stop sending clenching signals. As a result, he finds relief from the unsettling phantom hand sensation.

Thai chi, yoga and other balance exercises are some of the common ways to treat proprioception issues.

CARLINA TETERIS/GETTY IMAGES

Total Loss of Proprioception

In rare cases, people can lose all sense of proprioception. In his book of case studies, Sacks describes the case of Christina. The 27-year-old woman appears to have a reaction to medication in which the sensory roots of her spinal and cranial nerves become inflamed. Afterward, she suddenly lost the ability to steady herself while standing or holding objects in her hands. Within days, if not hours, she becomes “floppy as a ragdoll, unable to even sit up,” Sacks writes. Christina never regained her sense of self, but gradually, through rehabilitation and fierce concentration on her movements, she was able to sit up and walk again.

Another case of total loss proprioception was detailed in neurologist J. Cole’s book, “Pride and a Daily Marathon“. The book focuses on Ian Waterman who, at the age of 19, lost all sense of his body from his neck down after suffering a brief illness. Waterman described feeling as if he were just a head floating on a pillow. Like Christina, he never recovers, but with much therapy and determination, he is able to sit up and walk again.

While frightening to imagine, Shelley-Tremblay assures that total loss of proprioception is quite rare.

Treating Proprioception Impairments

The first line of defense when treating proprioception issues is to determine the underlying cause and treat that. Activities that focus on mobility, muscle strength and sense of balance may also help sharpen proprioception, according to a 2017 study in the Journal of Athletic Training.

Some of these therapies include:

• Physical therapy
• Somatosensory stimulation
• Balance exercises
• Tai chi
• Yoga

The bottom line is our sixth sense may be “hidden” from us, but proprioception plays a critical role in giving us a sense of ownership of our bodies. We may also take it for granted, but without it, we’d be, essentially, disembodied.