Proprioception

Proprioception (from Latin proprius, meaning "one's own" and perception) is the sense of the position of parts of the body, relative to other neighbouring parts of the body. Unlike the six exteroception human senses of sight, taste, smell, touch, hearing, and balance, that advise us of the outside world, proprioception is a sense that provides feedback solely on the status of the body internally. It is the sense that indicates whether your body is moving with required effort, as well as where the various parts of the body are located in relation to each other.

Kinesthesia is another term that is often used interchangeably with proprioception. Some users differentiate the kinesthetic sense from proprioception by excluding the sense of equilibrium or balance from kinesthesia. An inner ear infection, for example, might impact the sense of balance. This would impact the proprioceptive sense, but not the kinesthetic sense. The infected person would be able to walk, but only by using the person's sense of sight to maintain balance; the person would be unable to walk with his/her eyes closed.

Kinesthesia is a key component in muscle memory and hand-eye coordination, and training can improve this sense. The ability to effortlessly swing a golf club, or catch a baseball requires a finely tuned sense of the position of the joints, so that the eyes can concentrate on the ball and let the kinesthetic sense handle moving the body as needed to meet the ball.

Basis
The proprioceptive sense is believed to be composed of information from sensory neurons located in the inner ear (motion and orientation) and in the stretch receptors of joints and muscles (stance). There are specific nerve receptors for this form of perception, just like there are specific receptors for pressure, light/dark, temperature, sound, and other sensory experiences.

Applications
Proprioception is tested by American police officers using the field sobriety test where the subject is required to touch his nose with his eyes closed. People with normal proprioception may make an error of no more than 2 cm. People suffering from impaired proprioception (a symptom of moderate to severe alcohol poisoning) fail this test due to difficulty locating their limbs in space relative to their noses.

Proprioception is what allows someone to learn to walk in complete darkness without losing balance. During the learning of any new skill, sport, or art, it is usually necessary to become familiar with some proprioceptive concerns specific to that activity. Without the appropriate integration of proprioceptive input, an artist would not be able to brush paint onto a canvas without looking at the hand as it moved the brush over the canvas; it would be impossible to drive an automobile because a motorist would not be able to steer or use the foot pedals while looking at the road ahead; we could not touch type or perform ballet; and you would not even be able to walk without literally "watching where you put your feet".

The proprioceptive sense can be sharpened through study of many disciplines. The Alexander Technique uses the study of movement to directly enhance kinesthetic judgment of effort and location. Juggling trains reaction time and spatial location and efficient movement. Standing on a wobble board is often used to retrain or increase proprioception abilities, particularly as physical therapy for ankle or knee injuries. Standing on one leg (stork standing) and various other body position challenges are also used, in such disciplines as Yoga. A large part of what is called the Fourth Way, developed by G. I. Gurdjieff, involves a substantial amount of proprioceptive exercises which are said to assist in spiritual development. Several studies have shown that the efficacy of these types of training are challenged by closing the eyes, because the eyes give invaluable feedback to establishing the moment to moment information of balance.

Oliver Sacks once reported the case of a young woman who lost her proprioception due to a viral infection of her spinal cord. At first she was not able to move properly at all. Later she relearned by using her sight (watching her feet) and vestibulum (or inner ear) only. She eventually acquired a stiff and slow movement, which is believed to be the best possible in the absence of this sense. She could not judge effort involved in picking up objects.

David Bohm introduced the concept of "proprioception of thought." His ideas suggest that other people's points of view are needed, to be able to compensate for the inevitable self-deceptive assumptions of thinking. He wrote about proprioception in Thought As a System and his theories of "Dialogue."

Impairment
Apparently, temporary loss or impairment of proprioception may happen periodically during growth, mostly during adolescence. Growth that might also influence this would be large increases or drops in bodyweight/size due to fluctuations of fat (liposuction, rapid fat loss, rapid fat gain) and muscle content (bodybuilding, anabolic steroids, catabolisis/starvation). It can also occur to those who gain new levels of flexibility, stretching, and contortion. The limb being in a new range of motion never experienced (or at least, not for a long time since youth perhaps) is effectively like acquiring a new skill, even if one is looking at it. Looking at a limb where it isn't 'supposed' to be can throw off one's sense of placement, though not to as large a degree.

Possible experiences include: suddenly feeling that feet or legs are missing from your mental self-image; the need to look down at arms, hands, legs, etc. to convince yourself that they are still there; falling down while walking, especially when attention is focused upon something other than the act of walking (e.g., looking at a person who started talking or reading a billboard).

The proprioceptive sense can become confused because humans will adapt to a continuously-present stimulus; this is called habituation or desensitization. The effect is that it seems as though proprioceptive sensory impressions disappear, just as a scent seems to disappear when a person smells it for a prolonged period of time. One practical advantage of this is that unnoticed actions or sensation continue in the background while an individual's attention can move to another concern. The Jordan Technique addresses these issues.

People who have a limb amputated may still have a confused sense of that limb existence on their body, known as Phantom Limb Syndrome. Phantom sensations can occur as passive proprioceptive sensations of the limb's presence, or more active sensations such as perceived movement, pressure, pain, itching, or temperature. The etiology of the phantom limb phenomenon is still being disputed, but contemporary theories tend more towards neurological (e.g. neural signal bleed across a preexisting sensory map, as posited by V.S. Ramachandran) rather than psychological explanations. Phantom sensations and phantom pain may also occur after the removal of body parts other than the limbs, e.g. after amputation of the breast, extraction of a tooth (phantom tooth pain) or removal of an eye (phantom eye syndrome).

There is at least one documented case of a person losing their proprioceptive sense entirely, which is discussed in Oliver Sacks' book The Man Who Mistook His Wife for a Hat.

Temporary impairment has also been known to occur due to an overdose of vitamin B6 (pyridoxine and pyridoxamine). Most of the impaired function discontinues shortly after the intake of vitamins returns to normal. Impairment can also be caused by cytotoxic factors such as chemotherapy. An easily observed example of temporary proprioceptive impairment can be seen in drunk individuals undergoing sobreity tests (trying to touch their noses).

It has been proposed that even common Tinnitus and the attendant hearing frequency-gaps masked by the perceived sounds may cause erroneous proprioceptive information to the balance and comprehension centers of the brain, and precipitating mild confusion.

Permanent impairment: Proprioception is also reduced in patients who suffer from joint hypermobility or Ehlers-Danlos Syndrome (a genetic condition that results in weak connective tissue throughout the body).