Your sixth (and seventh) sense

Many, many years ago at school I was taught that there are five main senses: sight, hearing, taste, smell and touch. There was also some talk about the weird spooky Sixth Sense, and to show my age this was was long before that film came out.  I’m assuming that is the same for you, but were you aware that we have at least two or three more senses within our body: proprioception, interoception and nociception. OK, I’m sticking with the physical body here, so not going into spooky realms of the electrical field that surrounds us, the aura and Extra-Sensory Perception (ESP).

The Big Five senses give us information about the external world and how we interact with the space around us. We receive an external stimulus (light, odour, sounds, an impact or touch on our skin or we put something in our mouths) into specific organs or areas which have specialised sensory nerve cells in these areas that send information about the stimulus to the brain.   The information is then processed in specific areas in the brain that then interpret this information to tell us about our immediate surroundings.  The other less well known senses provide us with information about the internal state of our bodies as we travel through the world and our daily lives.

From an evolutionary perspective, sight is the most recently developed and uses the most brain activity. Touch is one of the oldest, with smell and it’s twin taste being very linked with determining the presence of noxious substances in our environment and food.  Hearing appearing sometime after (oh, maybe that’s yet another area of investigation for me, but not just yet).   For most of us these work really well, with some variability between individuals based upon genetics. Thinking about some of the optical illusions or “that dress” things that pass through the filters of the interweb.  Sight is also the easiest one to be tricked with optical illusions.

I’m not going to spend too much time here about the Big Five senses, as most of us will have covered them in school; even if that information is from quite some time ago and there might be some updates: another blog and another time.  This is also a massive subject (I do like to challenge myself) so this is a very, very, brief summary of the proprioceptive, interoceptive and nociceptive and so if any inaccuracies arise it’s my fault, and just drop me a line to let me know.   

Proprioception

Proprioception is possibly the one that more people are aware of, especially if they have a personal trainer, attend movement therapy classes (yoga, pilates etc) or have received some form of rehabilitation for an injury. Proprioception is the internal sense of how the parts of our bodies are organised in relation to each other and also how they are all moving in space and time.  The proprioceptive sensors are generally found in the muscles, the tendons and around the joints.  They measure the amount of effort a muscle is exerting, whether the tendon is under a safe level of tension among many other things.  These have a feed back system that allows us to adapt the amount of effort we need to complete the task at hand: increasing the muscular effort if something is heavier than expected, or hopefully reducing effort and stopping in time if somthing is lighter than expected.

For example, take both arms out to the sides, point both index fingers, can you bring those two finger tips together to touch? How did you do?  The ability to bring the hands together relies on the information in the joints and muscles of the hands, arms and shoulders, to tell the brain where they are moving and how fast. The brain interprets the information and co-ordinates what is going on.  Did you watch your hands and fingers as you did this task?

Now try the same thing with your eyes closed? How did you do? Was it harder? It probably was, and you might have completely missed touching the fingers together, at least the first time. This is because we use our sight to assist the proprioceptive sense, and if we remove the visual stimulus our body has to listen to information from sensors that it might not have been paying great attention to.  With practice this will improve. 

Try going slower and faster with this movement.  Are you equally accurate when you go quickly as you are when moving slower?  Slower movement will allow your proprioceptive sense to analyse what’s going on and so you should be more accurate than when you move quickly. 

Proprioception is also a big part of how we stay upright as we move through the world.  The joints, ligaments and muscles in the foot respond to each step allowing us to deal with changing terrain under our feet. This should allow us to easily keep upright as we walk, and I talk more about the foot in this blog. Shoes and the eternal flattening and smoothing of the world will reduce the amount of stimulation our proprioceptive sense gets and that could make us less likely to be completely able to cope with variable terrains.

For those of us who are lucky enough to have our sight we also use our vision to keep us upright, which is why if you stand on one leg you will find it much harder to remain steady if you close your eyes.  There is a very famous gentleman called Ian Waterman, who due to an illness lost all his proprioceptive awareness (the illness triggered antibodies that attacked the nerves) and whilst he could still feel heat, pain he had no awareness of where his body was if it was out of his sight. The BBC programme Horizon ran an episode looking at him called “The Man who lost his Body”. Ultimately, he learnt to walk again, but only by looking at his body and consciously moving it to where it needed to be.  Without his sight he would fall over.

Throughout the body, the Fascial system contains a significant number of mechanoreceptors that combine to help provide our proprioceptive sense.  These are more dense around the joints and the myotendinous (muscle/tendon) joints, which makes sense as proprioception is the awareness of how we are moving in relation to ourselves, the world around us in gravity.  There is fairly recent research that the retinacular of the ankles are full of proprioceptive sensors, and not so inert as they were previously thought.  The retincaular  are thickening in the ligament sheathe around the ankles.  They often get damaged when we sprain our ankles, and the constant signalling of pain we get can make the brain almost reduce the volume (or mutes) the importance of the signals whilst we are healing.  That helps us get around, but if we don’t remind the brain that this information needs to be listened to it can forget to restore the volume of the signals and that can impair our proprioceptive ability and make the rest of the body less able to function.  We still get on with things and can function, but we may not be quite as adaptive we could have been.

Walking around barefoot is one of the best ways of keeping the awareness into our proprioceptive system from the feet up.  This is where things like Yoga, Pilates, and SMFR Therapy can really help.  These are ways of moving with an awareness, especially with different speeds of movement, so we are listening to our proprioceptive sense with an awareness and giving ourselves a chance to respond.

Nociception

This is the least pleasant sense, but is pretty important, and it is the awareness of harm to the body, which is often reacted to as pain.   Nociception is often described as a separate sense as a theory was put forward that there are specific sensors (called nociceptors) in the body that send signals of pain to the brain.  However, research has shown that there are no  no specific receptors that detect pain, but instead they are the same sensors that give us information about proprioception and interoception but they think the intensity or amount of information is potentially threatening.  I discussed the fact that pain is an output from the brain in this blog.

The nerve endings that are responsible are detecting thresholds of issues such as thermal (heat/cold), pressure, and chemical.  A certain threshold needs to be met which then triggers a response in the nerves that makes them send a message to the brain saying that they are perceiving a potentially dangerous situation.  An example a group of people standing arond the bonfire might enjoy the warmth and light, but person could  shout fire if they think it’s dangerous. That person might be correct, but only when more of the group agree and start shouting fire could someone actually take action and put the fire out.

The receptors can be tricked by events that don’t exceed the threshold: such as when we get burnt by the sun, or lying against a slightly above body temperature radiator could cause severe bodily burns as we essentially slow cook.  We can also ignore the sensors based on context: your body routinely rests its weight on your backside each time you sit.  This is a significant amount of pressure exerted on that area, and most of us can happily sit for some time.  In fact we can comfortably sit for long periods without us thinking we’re hurting ourselves.  If that amount of pressure was placed on our upper arm we would react very differently.  After a time, which will also depend on what we are sitting on, we will start to feel uncomfortable and move.

The fact that there are no specific sensors in the body for nociception actually means that the sense that is referred to as Nociception is really just a subdivision of the next one: Interoception.

Interoception

This is the one you may not consciously be aware of, but you constantly use it.  Interoception is the awareness of how you physically feel: warm, cold, thirsty, hungry, satiated, aroused, needing to go to the toilet.  As I said the nociceptive sense is a part of this, as it actually uses the same information but we label it as harmful (basically more of the sensors are triggered or shouting louder) if our brain interprets it as painful (whether we are actually threatened with harm or not).

Check in with your body: take a couple of breaths and become aware of how your body feels.  It can be very difficult as we often ignore our body sensations as we can postpone acting on them until later: are you feeling cold? Too warm? Are you thirsty? Do you need to go to the toilet? Is the chair you’re sitting on making your bottom ache?

These are all things that we can have a conscious control over, to a certain extent. We can delay acting on them until they are more convenient for us:

• I feel a bit thirsty but I don’t have any water with me. I’ll wait until I get to my favourite coffee shop and get a drink there. 
• I’m hungry, but my lunchbreak isn’t for another hour. 
• I’m not hungry, but I really want to have another slice of cake.
• I feel cold, but I don’t like wearing jumpers. 
• I’m tired, but I want to finish this book, even though I need to get up early tomorrow.

Do these sound familiar?  In the short term there is nothing wrong with these delaying tactics, and short term can be each and every day.  However, in the long term routinely ignoring discomfort may well cause us to withdraw from noticing how we truly feel.  There may be very valid reasons we think that, we may have the drive to achieve some personal goal, or it might be more pernicious in that we think that our body is letting us down or is weak for having these feelings.  

I can remember when I was working in an office having to fit certain expectations, and that’s true now when I’m in clinic: I’m with a client I can’t stop to have a drink, or go to the toilet I’ll have to wait.  It is ok to delay things if I then actually have that water after the client has left.

I am pretty good at making sure I go to the loo if I need to, that is one we are all pretty certain we deal with.   In fact we may become over concerned about needing to go to the toilet, which I was told was called a “JIC pee” by the Pelvic Floor Physiotherapist who was running the Myofascial Release for Pelvic Floor course I attended in February 2020.  JIC stands for Just In Case, and it’s that going to the loo even if you don’t really need to before a long journey.  Our brain over rules the actual state of the body, in this case the bowels, and we may start to not believe the sensations from our bowels and ultimately end up going to the toilet far more frequently than is strictly necessary.  

It is the long term muting of our response to our interoceptive awareness that is the problem.  This chronic ignoring of our body may end up creating physical issues conditions.  Long term dehydration can lead to kidney stones, which can be very painful when they get passed and they maybe the first time we’re aware of them, but they are impairing the good function of the kidneys.  Constantly having that extra slice of cake could raise your blood sugars and cause pre-diabetes or even diabetes (yes, I’m taking an extreme point) and increase your bodyweight and the associated health problems that can come with obesity.

We then become habituated to how things feel, even if they are not optimum for our body.  This can be particularly true for hydration and also for sleep.  Sleep is often something that we perceive as being a waste of time (I only need four hours of sleep: fake news), but we need it each and every day (and generally about 8 hours of sleep potential).  We may be Night Owls but force ourselves to get up early as getting up late is perceived by society as being lazy, when really we just are hardwired to go to sleep late and get up late.  We cope with being sleep deprived, but we are not thriving or being truly nice to our bodies.  I really do recommend that people read “Why we sleep: the new science of sleep and dreams” by Matthew Walker.

We are very good at only noticing our body when things start to go wrong and we experience pain.  This is fairly normal for humans, and in many circumstances we can make changes to how we live and start to rectify what needs to alter, such as drinking a bit more water throughout the day.  A favourite thought I have come across is “Listen to your body when it whispers, you won’t have to hear it scream.”

One of the aspects of Myofascial Release (MFR) and SMFRTherapy is that time is spent on noticing how your body feels at the time of treatment or class.  This is done from as much a non-judgemental point of view, just noticing and responding and being nice to your body.  I know that I can feel very tired or thirsty after treatments, the same after a Reiki treatment, as I have actually stopped and have started paying attention to the information my body is supplying the brain.

I particularly mentioned MFR and SMFRTherapy as there is research that suggests that the Fascial System has many, many more nerve endings in it than the skin and these are particularly attuned with monitoring how the body is and so the fascia is considered an Interoceptive organ as well as a proprioceptive organ.  Some people are now saying that the Fascia is the largest sensory organ in the body, taking the prize from the skin.