Monday, 16 February 2015

The real sixth sense

We all know of our five senses – smell, taste, sight, hearing and touch. But have you heard of our sixth sense? It’s called proprioception, and it is the sense of our own bodies. It’s the awareness of the relative position of different parts of our body in relation to our head. For example, right now you are aware of how your legs might be crossed whilst reading this post, even though you are not looking directly at them. Or if you’ve ever driven a car, you would know you don’t need to stare at your feet and hands the whole time you are driving in order to turn the steering wheel or press the pedals to a certain pressure to control the car. Everyday tasks such as these have proprioception, or position sense, to thank.

Proprioception works by processing information from sensory neurons within the inner ear and stretch receptors in muscles and ligaments. This sixth sense is something we all take for granted, and are not really even aware of until it is taken away from us. But what would happen if you lost your sense of where you were relative to the world around you?

Incredibly, there have been a few reported cases of this happening. 

The real sixth sense is proprioception; not quite as this movie suggests!
One of these is Ian Waterman, whose case was explored in a 1998 BBC documentary entitled “The Man Who Lost His Body”. Waterman’s problems started when he was 19 and suffered badly from an undiagnosed fever, which may have set off an autoimmune reaction. He found himself suddenly struck with desensitisation of his entire body – he still had feeling in his limbs but couldn't work out where they were unless he looked at them. Doctors at the hospital Ian was in at the time had never encountered anything like his case before, and when put through a series of tests it was found that all of Ian’s sensory nerves at roughly his neck level had been destroyed.

Unsurprisingly, Ian had extreme difficulty with seemingly simple tasks such as sitting up from lying down and standing, as he had no perception of where his limbs were in relation to 'himself'. It is hard to imagine how difficult it would be to do anything if you could only move by concentrating solely on the muscles and parts of your body needed for that movement. However despite doctors initial prognoses, he refused to be put into a wheelchair and was determined to get his life back to how it was before his fever. Through rigorous training and practising different movements over and over again, Ian over time has retaught himself to walk and lead a relatively normal life.

Ian Waterman
When the documentary was made, around 30 years had passed since Ian was diagnosed with a lack of proprioception. His movements shown on the documentary look impressively normal. However, it’s worth mentioning that you cannot reteach your body to have a sense of proprioception – every movement Ian makes, even 30 years later, is perfectly thought out and executed to appear as effortless as it would be for you or I. This means that if in the dark, Ian still cannot control his hands and arms accurately.

Oliver Sacks (one of my favourite neuroscientists – I have reviewed another of his books in a previous post) also reported on the case of a patient losing their sense of proprioception, this time dubbing the woman as “The Disembodied Lady”. The patient, who had prior to their accident been active and healthy underwent some routine surgery to remove gallstones and her gallbladder. However, the day before her operation the patient (called Christine) had an extremely vivid dream in which she was unsteady and unable to use her limbs. She was so distressed by the dream that she even asked for help from a psychiatrist, who dismissed the doubts as pre-operation worries. However, as the day progressed, Christine seemed to find her dream becoming true. She became less steady on her feet, and became more distressed. By the time it came to Christine’s surgery, she could only stand by looking at her feet for reassurance. She even lost her normal tone to her voice, and she could only speak in a monotone flat voice.

You need proprioception to understand your body's position relative to your environment
Doctors carried out tests on Christine and found that whilst her parietal lobes (involved in integration of sensory information) were working, there seemed to be no limbs for them to work with – she had a distinct lack of proprioception. It appeared Christine, like Ian, had lost her sense of 'self'. Christine also trained herself with strict monitoring of her movements and eventually was able to regain some use of her limbs back, albeit only with visual aid. What I found most interesting in Christine’s case was how the lack of proprioception affected her voice. We tend to think of the tone of our voices as just a part of ourselves - we inherit our accent and pronunciation from our parents and alter it slightly to be our own version, the same way our hair happens to be the colour it is. However, it hadn’t occurred to me that the tone and distinct sound of our voices is determined mostly by impulses from all our vocal organs, including our vocal chords – something we cannot see. Therefore, Christine had huge difficulty in regaining her voice back, and Sacks reported that it became “a stagey, theatrical voice… because there was still no natural vocal posture”.

A fitting quote from Wittgenstein (an Austrian-British philosopher) that Sacks mentions in his book is;

“The aspects of things that are most important for us are hidden because of their simplicity and familiarity. (One is unable to notice something because it is always before one’s eyes.) The real foundations of his enquiry do not strike a man at all.” 

If you would like to learn more about Ian's case, his documentary can be viewed here


  1. Interesting post, looking forward to your future posts :) xx

  2. Wow! This is one of the most bizarre things I've ever heard of!? It must be such a difficult thing to try and treat? xx

    1. Exactly - fortunately cases like this are extremely rare!

  3. Really interesting post. Never heard of the position sense, proprioception, before. Enjoy your blog, always learn something new.

  4. Interesting! i dont thing i understood much but im still confused.. haha i think I need to read again #blondes ;p