We have the five senses we all know about: sight, hearing, smell, taste and touch (tactile). Then we also have our sense of proprioception (our body awareness – where our body is in space) and vestibular (movement). We’re going to look at tactile, proprioception and vestibular in more detail. These are very important in child development; as they get integrated (this refers to the way the receptors on our skin, in our eyes and so on receive the information, and how our brains process it, and therefore how we react to it).
Our sense of proprioception is really important. When we’re born – we tend to be all flexed up in a ball, and this physiological flexion gives us proprioception: i.e. it tells us where we are and is reassuring, along with touch from Mum or Dad, being cuddled. We can see that we need this as, if we lay a baby on the floor with nothing touching them, they startle – as they don’t know where their body ends and the world begins. We get our proprioception from the receptors in our joints and our muscles. They send signals up to the brain and tell you where your limbs are. So if you clench your fist or wiggle your fingers, you can feel your hand; whereas if you just let your hand lie still, it’s more difficult to feel exactly where the hand is. Proprioception relies on movement of the joints and stretch or activation of the muscles. As you develop; start to hold your head upright in the midline, roll over, push through your arms on your tummy, sit up and balance using the muscles in your trunk, stand and put pressure through your legs and eventually start to walk, you are building your body map, using the pathways between the proprioceptors and the brain.
Alongside all of this we receive tactile information through receptors in the skin. The information is carried along two different tracts or pathways up the spinal cord and into the brain: light touch along one tract, and deeper pressure along the other. All of this tactile information that we receive as babies (from being stroked, the feeling of our clothes, the pressure of the floor against our back or tummy or side) adds to the body schema and helps us to know where we are in space. That deep, firm touch is similar to proprioception; it’s quite calming, organising, it helps us to know where we are and feel safe. If you’re getting worked up and you clench your fists and bite down – or have a hug – it can help to calm and relax you. The light, more tickly type of touch can be a bit arousing and exciting; it can make you shiver or giggle. It goes up the same tract as pain and it’s more exciting than calming.
Your sense of vestibular or movement is affected by where your head is in relation to your body. Your eyes feed into the vestibular system in your inner ear. The system has two different types of receptors: firstly, there are sponge-like, linear structures (called otoliths), which tell you whether you’re moving up or down, or forwards or back; secondly there are the semi-circular canals, like little cups of water, which tell you whether you are tipping or spinning. The vestibular system is very important in terms of your balance. As different types of touch can be either calming or exciting, so too can input to the vestibular system. Linear, forwards-and-backwards movements that stimulate the sponge-like receptors can be calming and organising and help you to focus. If the semi-circular canals are stimulated, this is arousing – it’s telling you that you’re tipping or falling and you need to correct yourself. This is why riding on a rollercoaster or spinning round and round can make you feel giddy and excited (or dizzy or nauseous!). If you’re feeling sleepy, tipping your head from side to side or turning upside down can be a good way to wake yourself up.
Think of a toddler, toddling around. Generally they do lots of climbing, jumping off things, they’re running in the park, they’re on the swings, the roundabout… They’re constantly exploring their body, their muscles and joints are working so they’re getting lots of proprioception (so that’s calming and organising). Your receptors are being stimulated – you’re touching the grass, the climbing frame, the sofa, the carpet, the floor, your whole body is getting different types of touch, you’re rolling on the ground. Also you’re stimulating the movement sensors in combination with these things. You might be spinning around, you might be climbing up and down things, you’re doing a good mixture of things that are exciting to the system, along with things that dampen down that excitement. That’s what’s called regulation – it keeps you in a good calm, alert state and means that you can still focus on the world around you. You can still listen if your mum and dad are calling you, you can still think and plan what you’re going to do so that you can stay relatively safe. This is the calm, alert state of arousal that you’re in when you’re not so sleepy or under-aroused that you’re not aware of things around you – so that you might trip over a kerb, you might not attend to a noise like somebody calling your name, you might not see someone waving at you – and equally you’re not over-aroused, so you’re not too excited or too giddy or too upset that you can’t calm yourself down in order to be able to sit still in the classroom, to do good listening, to learn, to function. The calm, alert state – somewhere in the middle – allows you to listen to the things you need to listen to, and zone out the things you don’t need to attend to.
This is called sensory integration. As children develop, move around and explore, their senses naturally become integrated. All the information from all the receptors goes up the pathways or tracts into the brain and is processed, and anything that definitely needs to be flagged to remember for next time – such as a green or red light when you’re crossing the road, or a car coming towards you, or your mum saying “Stop!” or “That’s really hot!” – those kind of flags get an immediate response because you’ve learnt that over time. Equally things that you’ve realised you can zone out – things that happen all the time such as doors closing, noises in the night, noises in the classroom while you’re paying attention to the teacher – you habituate (get used) to them and you don’t listen to them. That’s if you have good, typical sensory processing.
So What is Different if a child has Cerebral, Palsy?
If you have a child with cerebral palsy, whose independent physical mobility is restricted – maybe their movement patterns are not typical, they might move their arms and legs more in one direction than another, or use certain muscles more than others to
activate movement, maybe certain parts of their body might get more touch than other parts – they might have missed the tummy time stage for example, or the rolling stage (rolling over and over is really good for body awareness, for learning where your body ends and the floor begins). They might have missed the crawling stage, when you’re getting weight bearing through the shoulders, elbows and wrists, through the knees and up into the hips, it’s activating the joints, it’s telling your body where it is in space, if you miss that stage then you’re going to miss out on that proprioception or body awareness. Your body schema (body map) will not be typical, and your perception (e.g. of where the midline is) will be altered. Remember the proprioceptors are the calming, organising inputs that help you to focus and organise and dampen down any excitatory inputs. Your touch receptors – if your hand is closed most of the time you are not going to have experienced lots of different types of touch on your palm.
Your movement sensors… If your head hasn’t been in the upright position in lots of different ways – when you’re lying on your tummy and lifting your head for the first time, when you’re learning your head control, and then when you’re starting to balance in sitting and then standing, using a mixture of your flexors and extensors (the muscles on the front and back of your body), getting that co-contraction – all of these things feed into your balance and your vestibular system. If you haven’t had that, or maybe experienced this in an asymmetrical pattern, then your vestibular system will have an altered perception of what is upright.
How quickly your body responds to you falling sideways, for example, will depend on how well integrated the receptors of that system are, whether the receptors are receiving the information at all, whether enough input has been put into the system for the receptors to have sent it up to the brain, or whether they are over-sending so you’re constantly responding to the information because maybe your muscle tone is high and it’s sending signals all the time.
So not surprisingly, children with cerebral palsy have some difficulty with their sensory integration, and this can affect therefore their calm alert state – so their ability to regulate their emotional state, to calm down when they’re upset, to regulate how excited they get and how they respond to that excitement, to be able to continue with a task if a distraction has caught their eye or some auditory information has come in, to be able to think to themselves “I don’t need to attend to that, I’m going to carry on with what I’m doing”.
You might see that a child can perform a particular task in one situation – when they’ve been doing something prior to that maybe – but then in another situation they can’t do it, and you think, “I know they can do this, but they’re not performing right now.” It may be that the situation that they’re in, the environment that they’re in or the preparation they’ve had affects their performance and their function. This can have a big impact on their learning in school, if one environment they learn or perform well in, whereas other environments they maybe don’t.
Part of our role as Physiotherapists and parents and carers is to ensure that no matter what your child’s physical ability they get to experience a wide range of play activities, positions and movements to build their library of sensory experiences and organise the sensory input so they can attend and respond to stimuli and adapt in new environments, to be more effective learners and players and ultimately successful adults.