Proprioception, from Latin proprius, meaning "one's own", "individual" and perception,
is the sense of the relative position of neighbouring parts of the body and strength of effort being
employed in movement.
It is provided by proprioceptors in skeletal striated muscles and in joints.
It is distinguished from exteroception, by which one perceives the outside world, and
interoception, by which one perceives pain, hunger, etc., and the movement of internal
organs.
The brain integrates information from proprioception and from the vestibular system into its overall
sense of body position, movement, and acceleration.
The word kinesthesia has been used inconsistently to refer either to proprioception alone or
to the brain's integration of proprioceptive and vestibular inputs.
History of study The position-movement sensation was originally
described in 1557 by Julius Caesar Scaliger as a "sense of locomotion".
Much later, in 1826, Charles Bell expounded the idea of a "muscle sense" and this is credited
with being one of the first described physiologic feedback mechanisms.
Bell's idea was that commands are carried from the brain to the muscles, and that reports
on the muscle's condition would be sent in the reverse direction.
Later, in 1880, Henry Charlton Bastian suggested "kinaesthesia" instead of "muscle sense" on
the basis that some of the afferent information was coming from other structures including
tendons, joints, and skin.
In 1889, Alfred Goldscheider suggested a classification of kinaesthesia into three types: muscle,
tendon, and articular sensitivity.
In 1906, Charles Scott Sherrington published a landmark work which introduced the terms
"proprioception", "interoception", and "exteroception".
The "exteroceptors" are the organs responsible for information from outside the body such
as the eyes, ears, mouth, and skin.
The interoceptors then give information about the internal organs, while "proprioception"
is awareness of movement derived from muscular, tendon, and articular sources.
Such a system of classification has kept physiologists and anatomists searching for specialised nerve
endings that transmit data on joint capsule and muscle tension.
Muscle spindles are widely believed to play a large role in proprioception.
Primary endings of muscle spindles "respond to the size of a muscle length change and
its speed" and "contribute both to the sense of limb position and movement".
Secondary endings of muscle spindles detect changes in muscle length, and thus supply
information regarding only the sense of position.
Essentially, muscle spindles are stretch receptors.
It has been accepted that cutaneous receptors also contribute directly to proprioception
by providing "accurate perceptual information about joint position and movement," and this
knowledge is combined with information from the muscle spindles.
Components A major component of proprioception is joint
position sense, which is determined by measuring the accuracy of joint–angle replication.
Clinical aspects of joint position sense are measured in joint position matching tests
that measure a subject's ability to detect an externally imposed passive movement, or
the ability to reposition a joint to a predetermined position.
These involve an individuals ability to perceive the position of a joint without the aid of
vision.
Often it is assumed that the ability of one of these aspects will be related to another;
however, experimental evidence suggests there is no strong relation between these two aspects.
This suggests that while these components may well be related in a cognitive manner,
they may in fact be physiologically separate.
More recent work into the mechanism of ankle sprains suggests that the role of reflexes
may be more limited due to their long latencies, as ankle sprain events occur in perhaps 100
ms or less.
In accordance, a model has been proposed to include a 'feedforward' component of proprioception,
whereby the subject will also have central information about the body's position before
attaining it.
Kinesthesia is a key component in muscle memory and hand-eye coordination, and training can
improve this sense.
The ability to swing a golf club or to catch a ball requires a finely tuned sense of the
position of the joints.
This sense needs to become automatic through training to enable a person to concentrate
on other aspects of performance, such as maintaining motivation or seeing where other people are.
Basis of proprioceptive sense The initiation of proprioception is the activation
of a proprioreceptor in the periphery.
The proprioceptive sense is believed to be composed of information from sensory neurons
located in the inner ear and in the stretch receptors located in the muscles and the joint-supporting
ligaments.
There are specific nerve receptors for this form of perception termed "proprioreceptors,"
just as there are specific receptors for pressure, light, temperature, sound, and other sensory
experiences.
Proprioreceptors are sometimes known as adequate stimuli receptors.
TRPN, a member of the transient receptor potential family of ion channels, has been found to
be responsible for proprioception in fruit flies, nematode worms, African clawed frogs,
and zebrafish.
The human proprioceptor has yet to be discovered.
Proprioception of the head stems from the muscles innervated by the trigeminal nerve,
where the GSA fibers pass without synapsing in the Gasserian ganglion, reaching the mesencephalic
tract and the mesencephalic nucleus of trigeminal nerve.
Although it was known that finger kinesthesia relies on skin sensation, recent research
has found that kinesthesia-based haptic perception relies strongly on the forces experienced
during touch.
This research allows the creation of "virtual", illusory haptic shapes with different perceived
qualities.
Conscious and unconscious proprioception In humans, a distinction is made between conscious
proprioception and unconscious proprioception: Conscious proprioception is communicated by
the posterior column-medial lemniscus pathway to the cerebrum.
Unconscious proprioception is communicated primarily via the dorsal spinocerebellar tract
and ventral spinocerebellar tract, to the cerebellum.
An unconscious reaction is seen in the human proprioceptive reflex, or righting reflex
– in the event that the body tilts in any direction, the person will cock their head
back to level the eyes against the horizon.
This is seen even in infants as soon as they gain control of their neck muscles.
This control comes from the cerebellum, the part of the brain affecting balance.
Applications Field sobriety test
Proprioception is tested by American police officers using the field sobriety test to
check for alcohol intoxication.
The subject is required to touch his or her nose with eyes closed; people with normal
proprioception may make an error of no more than 20 millimeters, while people suffering
from impaired proprioception fail this test due to difficulty locating their limbs in
space relative to their noses.
Diagnosis There are several relatively specific tests
of the subject's ability to proprioceive.
These tests are used in the diagnosis of neurological disorders.
They include the visual and tactile placing reflexes.
Learning new skills 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 tasks 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 pedals while looking at the road ahead; a person could not touch type or perform
ballet; and people would not even be able to walk without watching where they put their
feet.
Oliver Sacks has reported the case of a young woman who lost her proprioception due to a
viral infection of her spinal cord.
At first she could not move properly at all or even control her tone of voice.
Later she relearned by using her sight and inner ear only for movement while using hearing
to judge voice modulation.
She eventually acquired a stiff and slow movement and nearly normal speech, which is believed
to be the best possible in the absence of this sense.
She could not judge effort involved in picking up objects and would grip them painfully to
be sure she did not drop them.
Training
The proprioceptive sense can be sharpened through study of many disciplines.
Examples are the Feldenkrais method and the Alexander Technique.
Juggling trains reaction time, spatial location, and efficient movement.
Standing on a wobble board or balance board is often used to retrain or increase proprioception
abilities, particularly as physical therapy for ankle or knee injuries.
Slacklining is another method to increase proprioception.
Standing on one leg and various other body-position challenges are also used in such disciplines
as Yoga, Wing Chun and T'ai chi.
Several studies have shown that the efficacy of these types of training is increased by
closing the eyes, because the eyes give invaluable feedback to establishing the moment-to-moment
information of balance.
There are even specific devices designed for proprioception training, such as the exercise
ball, which works on balancing the abdominal and back muscles.
Joint position matching Joint position matching is an established
protocol for measuring proprioception, and joint position sense specifically, without
the aid of visual or vestibular information.
During such tasks, individuals are blindfolded while a joint is moved to a specific angle
for a given period of time, returned to neutral, and the subjects are asked to replicate the
specified angle.
Measured by constant and absolute errors, ability to accurately identify joint angles
over a series of conditions is the most accurate means of determining proprioceptive acuity
in isolation to date.
Recent investigations have shown that hand dominance, participant age, active versus
passive matching, and presentation time of the angle can all affect performance on joint
position matching tasks.
Joint position matching has been used in clinical settings in both the upper and lower extremities.
Impairment It has been seen that 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 and/or muscle content.
It can also occur in those that gain new levels of flexibility, stretching, and contortion.
A limb's being in a new range of motion never experienced can disrupt one's sense of location
of that limb.
Possible experiences include suddenly feeling that feet or legs are missing from one's mental
self-image; needing to look down at one's limbs to be sure they are still there; and
falling down while walking, especially when attention is focused upon something other
than the act of walking.
Proprioception is occasionally impaired spontaneously, especially when one is tired.
One's body may appear too large or too small, or parts of the body may appear distorted
in size.
Similar effects can sometimes occur during epilepsy or migraine auras.
These effects are presumed to arise from abnormal stimulation of the part of the parietal cortex
of the brain involved with integrating information from different parts of the body.
Proprioceptive illusions can also be induced, such as the Pinocchio illusion.
The proprioceptive sense is often unnoticed because humans will adapt to a continuously
present stimulus; this is called habituation, desensitization, or adaptation.
The effect is that proprioceptive sensory impressions disappear, just as a scent can
disappear over 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 Alexander Technique addresses these issues.
People that have a limb amputated may still have a confused sense of that limb's 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.
There are a variety of theories concerning the etiology of phantom limb sensations and
experience.
Jack Tsao, MD.
at Walter Reed Hospital has advanced a theory based on the concept of "proprioceptive memory."
This theory argues that the brain retains a memory of specific limb positions and that
after amputation there is a conflict between the visual system, which literally sees that
the limb is missing, and the memory system which remembers the limb as a functioning
part of the body.
Phantom sensations and phantom pain may also occur after the removal of body parts other
than the limbs, such as after amputation of the breast, extraction of a tooth, or removal
of an eye.
Temporary impairment of proprioception has also been known to occur from an overdose
of vitamin B6.
Most of the impaired function returns to normal shortly after the intake of vitamins returns
to normal.
Impairment can also be caused by cytotoxic factors such as chemotherapy.
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, precipitating mild confusion.
Proprioception is permanently impaired in patients that suffer from joint hypermobility
or Ehlers-Danlos Syndrome.
It can also be permanently impaired from viral infections as reported by Sacks.
The catastrophic effect of major proprioceptive loss is reviewed by Robles-De-La-Torre.
There is also some evidence that proprioception is impaired in autism spectrum disorders such
as Asperger Syndrome.
Proprioception is also permanently impaired in physiological aging.
See also
References
External links Neuroscience Tutorial See "Basic somatosensory
pathway", Eastern International College.
Joint & Bone – Ehlers-Danlos/Joint Hypermobility Syndrome – Proprioception
Humans have six senses, why does everyone think we only have five?
at Everything2 Proprioception this essay by Charles Wolfe
takes its cue from such thinkers & artists as Charles Olson, Merleau-Ponty, James J.
Gibson, and Andy Clark to illustrate the view of the "priority of dynamic embodied activity
over isolated 'mental' and 'physical' regions" to define this concept
WNYC – Radio Lab: Where Am I? radio program looks at the relationship between the brain
and the body The Dancers Mind ABC podcast on the nature
of proprioception.
Proprioception at the US National Library of Medicine Medical Subject Headings