The Mysterious Sixth Sense of Human Beings: Proprioception Bernice Ho

The Mysterious Sixth Sense of Humans: Proprioception Bernice Ho (Year 6, Fry)

INTRODUCTION

Imagine you have lost senses in your body and are not aware of your body movement, would you be scared? This is an experience that a man named Ian Waterman [1] must deal with for the rest of his life. Due to a rare autoimmune infection that attacked all his sensory neurons below his neck, he was left with the inability to feel the sense of touch and senses from below his neck. Without the feedback that comes with movement, Ian was unable to coordinate his movements in a meaningful way. When he had his eyes shut, he was completely unable to coordinate his muscle movement.

Proprioception is sometimes called the “sixth sense,” apart from the well-known five basic senses: vision, hearing, touch, smell and taste. Proprioceptive sensations are a mystery because we are largely unaware of them. This article explains how proprioception works in our body, how important it is to our daily life, and what we can do to improve it.

WHAT IS PROPRIOCEPTION?

Proprioception is the medical term that describes the ability to sense the orientation of our body in the environment. In other words, it is basically defined as our ability to sense exactly where our body is [2]. It works unconsciously in our body and allows us to move quickly and freely without having to consciously think about where we are in an environment.

Let’s try to feel our proprioceptive senses. Close your eyes and use your finger to point to your nose. Is it easy for you? Most of us should easily accomplish this little task. Why? PROPRIOCEPTION.

THE SCIENCE BEHIND PROPRIOCEPTION

Proprioception involves a complex signalling progress transferring proprioceptive signals from our body parts to the brain. It is a constant feedback loop within our nervous system, telling our brain what position we are in and what forces are acting upon our body at any given point in time.

Proprioception is mediated by proprioceptors, which are tiny little sensors located throughout our entire body, especially in the skin, joint and muscle, and mechanosensory neurons. There are multiple types of proprioceptors working in our body (Table 1).

The proprioceptive receptors are activated during distinct behaviors and encode distinct types of information such as limb velocity and movement, load on a limb, and limb limits. Thousands and millions of proprioceptive signals are sent to our brains through peripheral and central nervous

Figure 1: Muscle spindles as proprioceptors to transmit the signal of muscle stretch to the brain through the spinal cord. (Modified from Stevenlgourley,“Muscle spindles,” https://www.youtube.com/watch?v=F871bBWS4oY)

Table 1: Types of proprioceptors [3]

systems at the same time. Our brains do tremendous jobs to integrate all these proprioceptive signals together with other sensory inputs, such as touch, taste and smell, to create and fully complete presentation of body position, movement and acceleration.

Let’s take muscle spindle as a proprioceptor as an example. When we stretch our arm, the muscle in our arm relaxes and gets thinner. The muscle spindle also gets stretched out and can sense that the muscle has been stretched out. It fires a signal to the brain through the spinal cord. The brain processes the signal and generates awareness of the arm’s position (fig 1).

FACTORS THAT WEAKEN THE PROPRIOCEPTIVE SENSES

Reduced proprioception is when the proprioceptors do not work properly in receiving and sending information about the environment to the brain. Sicknesses like stroke, brain injuries and arthritis will lead the proprioception sense to work weakly.

Our proprioception capabilities can also be impaired when joints are injured, such as with ligament sprains. Pain associated with joint injury and inflammation also impairs proprioceptive accuracy. When we lose proprioception of our joint after a sprain, we may experience an unstable sensation of the joint. Our joint may even give-out.

Apart from injury, aging has been shown to reduce proprioception. This age related reduction can cause impaired postural control and increase the risk for all older individuals [4].

One important area of research is proprioceptive dysfunction. Researchers believe that proprioceptive dysfunction is one of the major causes for the sensory processing disorders which affect children [5]. Children with sensory processing disorders are unable to use their body effectively. They feel as if they’re not in control of their body and as a result they may have difficulty concentrating in school [6].

Children suffering from proprioceptive dysfunction are uncoordinated and have difficulty performing basic normal childhood tasks and activities. They don’t experience the world like the majority of people.

Without proper awareness of muscle status and joint position, children will have [7]: 1. Poor motor planning & body awareness such as difficulty understanding personal space or boundaries when playing with others 2. Poor self-regulation skills such as difficulty attending to task, mood swings, difficulty with sleep 3. Poor grading movement (i.e. how much pressure is needed to complete a task) 4. Poor postural stability such as rests head on desk while working, poor muscle tone, unable to balance on one foot 5. Sensory seeking behaviors such as taps or shakes feet while sitting, chews, pushes or hits others, writes too hard

Children with proprioceptive dysfunction such as Attention Deficit Hyperactivity Disorder (ADHD) are often full of energy, it is extremely difficult for them to focus on an activity for a prolonged period of time [8]. They can easily become frustrated, give up and lose self-confidence. Their struggles with proprioceptive dysfunction manifests in their learning environment.

HOW TO IMPROVE OUR PROPRIOCEPTIVE SENSES

“Practice makes perfect” is a key to improve the body’s proprioceptive senses. Those suffering from proprioceptive dysfunction can enhance their proprioception by regular training. Scientists have shown that proprioceptive training resulted in an average improvement of body movement by 52% across all outcome measures [9]. Proprioceptive training can be broadly categorised into 5 types of techniques [10].

1. Active movement and balance training These kinds of proprioceptive training require the patient to actively move limbs, segment of limbs or whole body. A common example of a balance exercise is the use of an unstable surface e.g. Foam, Harbinger, and BOSU (fig 3).

Figure 2: Balance exercises to improve proprioceptive senses using Foam, Harbinger & BOSU equipment [11]

2. Passive movement training As its name indicated, patient’s body parts are moved passively by an apparatus or machine (fig 3).

3. Somatosensory stimulation training This type of training employs external stimulation upon the patient's body such as electrical and magnetic stimulation, acupuncture, and vibration [13].

4. Somatosensory discrimination training

This type of training involves patients exploring opposing somatosensory stimuli and differentiating between them. For example, a patient explores different objects with their hand, discriminates between textures, or gauges the position of their wrist or ankle joints.

Figure 3: Passive movement training to improve a patient's proprioceptive sense [12].

5. Combined / multiple systems The combined / multiple systems employ two or more of the above methods to further enhance the training results.

SUMMARY

Proprioception is mysterious and involves a complex signalling process in our body. Scientific understanding of it is still limited and much of it is still waiting to be discovered. Without proprioception we wouldn’t be able to sense our body parts accurately. It affects our daily lives. Children suffering from proprioceptive dysfunction will experience learning delays in school and have to overcome more challenges than those without it. Although there are ways to help them to improve their proprioceptive senses, it is still very limited. Thanks to many brilliant scientists and researchers, I believe that in the future we can do more things to help them and crack more mysteries of our sixth sense.

[1] Simon Gandevia and Uwe Proske, “Proprioception: The Sense Within,” TheScientist, Aug 31, 2016, https://www.the-scientist.com/features/proprioception-the-sense-within-32940 [2] Khanacademy, “Proprioception and kinesthesia”, https://www.khanacademy.org/science/health-andmedicine/nervous-system-and-sensory-infor/somatosensation-topic/v/proprioception-kinesthesia [3] Prakash Jha, Irshad Ahamad, Sonal Khurana, Kamran Ali, Shalini Verma and Tarun Kumar, “Proprioception: An Evidence Based Narrative Review,” Res Inves Sports Med. 1(2). RISM.000506. 2017, p14, https://pdfs.semanticscholar.org/60b0/e483e5b17f2ffec286dedfc38bba79d384bb.pdf?_ ga=2.34305953.1453459681.1588401674-1888949605.1588401674 [4] Prakash Jha, Irshad Ahamad, Sonal Khurana, Kamran Ali, Shalini Verma and Tarun Kumar, “Proprioception: An Evidence Based Narrative Review,” Res Inves Sports Med. 1(2). RISM.000506. 2017, p15, https://pdfs.semanticscholar.org/60b0/e483e5b17f2ffec286dedfc38bba79d384bb.pdf?_ ga=2.34305953.1453459681.1588401674-1888949605.1588401674 [5] Sensory Processing Disorder, “Sensory Processing Disorder Through The Eyes of Dysfunction,” https://www.sensory-processing-disorder.com/sensory-processing-disorders.html [6] Sensory Processing Disorder, “Sensory Processing Disorder Through The Eyes of Dysfunction,” https://www.sensory-processing-disorder.com/sensory-processing-disorders.html [7] Sonoran Sun Pediatric Therapy, “ What is Proprioception and Why is it Important?,” https:// sonoransunpediatrictherapy.com/2017/11/16/what-is-proprioception-and-why-is-it-important/ [8] Integrated Learning Strategies Learning Corner, “Proprioceptive Dysfunction Causes Sensory Seeking and Sensory Avoiding Behavior,” https://ilslearningcorner.com/2016-04-proprioceptivedysfunction-causes-sensory-seeking-and-sensory-avoiding-behavior/ [9] Aman JE, Elangovan N, Yeh IL, Konczak J. The effectiveness of proprioceptive training for improving motor function: a systematic review. Front Hum Neurosci. 2015;8:1075. Published 2015 Jan 28, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4309156/ [10] Ausmed, “Five Evidence-Based Ways to Hone Proprioception,” https://www.ausmed.com/cpd/ articles/proprioception-training [11] Dr. Anjana’s Physiorehab, “Sense of Bodily Perception – Proprioception,” http://physiorehab.in/ sense-of-bodily-perception-proprioception/ [12] Ausmed, “Five Evidence-Based Ways to Hone Proprioception,” https://www.ausmed.com/cpd/ articles/proprioception-training [13] Wang, Y, Cao, L, Hao, D, Rong, Y, Yang, L, Zhang, S,Chen, F & Zheng, D 2017, ‘Effects of force load, muscle fatigue and extremely low frequency magnetic stimulation on EEG signals during side arm lateral raise task’, Physiological measurement, vol. 38, no. 5, p. 745, https://www.ncbi.nlm.nih.gov/ pubmed/28375851