Proprioception, our sixth sense

Proprioception contributes to the control of our movements -

• Proprioception is comparable to a GPS because it sends us location signals at all times, according to a study published by our partner The Conversation.

• It is a meaning still poorly understood because it is difficult to fake its loss or affection.

• The analysis of this phenomenon was carried out by Fabrice Sarlegna, CNRS researcher at the Institute of Movement Sciences, Aix-Marseille University (AMU).

Vision.

The hearing.

The smell.

Taste.

Touch.

Proprioception.

Proprioception?

How many know this meaning, which has been well studied since the 19th century, in particular by Claude Bernard, who gave his name to a university in Lyon, and the Englishman Charles Sherrington, who obtained the Nobel Prize for physiology / medicine in 1932. So what is proprioception?

What does it allow to feel?

Proprioception is the sense describing our ability to locate each of our body parts: it allows us to feel our own body.

Where is your right foot?

How is your left arm positioned?

Could you draw your body in its current configuration?

If you close your eyes, you will be able to answer these same questions, thanks to the integration by the central nervous system of the signals it receives on stretching muscles, tendons and skin.

Proprioception therefore gives us the advantage of perceiving our body constantly and precisely, even in the dark and when we are in motion.

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Being able to represent your body, implicitly or explicitly, is essential in our daily life.

Indeed, proprioception is comparable to a GPS, giving us location signals at every moment.

Otherwise, if you don't know where you are, how do you go to a place?

The proprioceptive sense allows the brain to determine, for all our body segments, their position, speed and direction.

This sense will thus help us to guide our movements so that they reach the set objective, and not only when we cannot see.

A prominent example of the functional role of proprioception is that of rare patients who have lost proprioceptive sense as a result of neuropathy, a pathology of the nervous system.

In this specific case, it is the peripheral nervous system that is damaged.

If we make an analogy between our body and our home, it is as if the electric cables no longer work.

If we look at an electrical diagram of each of these systems, it is as if “the generator” (the battery or the brain) and the “effector” (the bulb or the muscle) were working correctly, but the conductive element (the electric wire or the nerve) is injured as regards the part "coming full circle", that is to say the proprioceptive feedback on the state of the system (blue part) on the diagram of right.

diagrams © Fabrice Sarlegna 2020

In patients with sensory neuropathy, it is still possible to send information from the brain to the muscle (motor control).

Yet when the lesion appears, patients are paralyzed, unable to move for days on end.

The reason ?

Patients do not feel their body.

When a neurologist asks one of these patients if he can move his leg, the patient replies: "Yes Doctor, as soon as I find her".

This is what Oliver Sacks describes, who describes his encounters with extraordinary patients in his book

.

One of his meetings will be shot the poignant film

(1990), with Robin Williams and Robert de Niro, who plays the role of the patient Leonard.

Sacks will underline the importance of proprioception in his chapter “The disembodied woman”.

Christina is a 27 year old young woman who declares that she no longer feels her body, that she is disembodied.

Neurologists have never seen this.

She has lost proprioception.

When a "hammer blow" or a vibrator is applied to his patellar tendon, no reflex movement… The consequences on his voluntary movements are also serious.

Christina has difficulty standing and needs to constantly watch her feet.

Even watching her hands closely, she can hardly use them for her daily actions, missing the intended object as if she has lost control of the gesture.

Sacks will discover that Christina is not unique, that many people have developed similar neuropathies from taking too much vitamin B6.

But this is not the case with Ginette, or even with Ian, whose journey is told in a BBC report (

) and in Jonathan Cole's books,

and

.

Ginette and Ian lost proprioception presumably as a result of an autoimmune reaction.

It is difficult to understand their sensory deficit, because we cannot simulate a loss of proprioception as we can simulate a visual loss by blindfolding, or a hearing loss by blocking the ears.

This contributes to the fact that proprioception is a poorly understood meaning.

In addition, proprioception is a sense that contributes automatically, unconsciously, to the control of our movements.

But this fundamental role is clear when we observe the motor skills of these patients.

It is only after months of training that the patients come out of their paralysis and manage to move the head, then the trunk, the arms, and little by little to find a certain overall coordination in order to stand up, maintain a sitting posture.

But standing and walking are often too dangerous a function due to the risk of falling: the majority of patients are required to use a wheelchair.

Grabbing objects can be re-learned, but manual dexterity is still limited.

Peeling a few potatoes can take an hour for Ginette, who has yet been able to get used to her proprioceptive loss dating back 40 years.

Without proprioception, gripping small objects is difficult.

When a clinical test is to be performed to assess manual dexterity, putting small objects in small receptacles takes almost a quarter of an hour for a patient, while a normal person takes little more than a minute.

Without proprioception, making a successful movement and repeating this performance is almost impossible, even with vision, which therefore does not completely compensate for the loss of proprioception to ensure normal motor control.

That said, vision has an essential role: Ginette can write or drink when she sees her hands, as we can see in the recent documentary

.

Without vision, the arm drifts, seemingly out of control.

If we ask a person with a major proprioceptive deficit to hold a glass at shoulder level, as in the photos below, we observe that with open eyes, the glass is well maintained (photo from the left).

In the photo on the right, the patient closed her eyes and did not feel the descent of her arm or the rotation of her wrist.

Gina with a cup of coffee © Fabrice Sarlegna 2020

You might say to yourself, “Fortunately proprioceptive deficits don't concern me.

"… But this thought is wrong… As a person ages, visual deficits appear.

Hearing deficits too.

Proprioceptive deficits too.

As a person ages, an ophthalmologist precisely quantifies visual deficits, and an optician prepares corrective glasses.

If hearing deficits are detected, a hearing care professional comes to our aid with a hearing aid.

But today, in 2020, more than 2,000 years after Aristotle identified 5 senses, the proprioceptive sense remains unknown.

As a result, there is no protocol or clearly identified specialist to quantify proprioceptive acuity, detect any proprioceptive deficit and then assess the progress of rehabilitation.

Considering the functional importance of proprioception, which is a major sense for maintaining balance and coordinating our most basic movements, it is necessary to develop exchanges between researchers, physiotherapists, psychomotor therapists, sports educators and those in charge of health system.

The stakes are high since proprioceptive deficits partly explain the difficulties observed in the daily life of the elderly, or obese, having had a Cerebral Vascular Accident, suffering from multiple sclerosis or Parkinson's disease ... By now that a real work chain is established, it is better to maintain, or improve, your proprioception with physical activity adapted to your profile!

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This analysis was written by Fabrice Sarlegna, CNRS researcher at the Institute of Movement Sciences, Aix-Marseille University (AMU).

The original article was published on The Conversation website.

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