Know your Neurobiology: The Proprioceptive System Part 1
Proprioception gives us our senses of position and movement throughout our body, it gives the sense of effort, force, heaviness, stretch, speed of movement. It knows where body parts are without seeing them.
Together with tactile and interoception it gives us a body scheme. Together with vestibular and vision it enables us to maintain postures and to move. Together with tactile and vision it enables us to explore objects and copy others. So, as you can see, it is fundamental.
But proprioception also allows us to be embodied, to know exactly where we are and who we are. In his book ‘The man who mistook his wife for a hat’ Oliver Sacks describes Christina who lost her sense of proprioception in this way: …”she felt that her body is dead, not hers, she cannot appropriate it to herself ”. In Christina’s ownwords: “I can’t feel my body. I feel weird — disembodied…I feel my body is blind and deaf to itself… it has no sense of itself.” Oliver Sacks 1985
Proprioceptive sensation is generated as a result of our own actions. It creates a continuous feedback loop between the populations of different sensory receptors (mechanoreceptors) located in our muscles, joints, tendons and skin (stretch receptors) and the structures in our central nervous system (spine, brainstem, cerebellum and somatosensory cortex, limbic structures – to name just some).
As we engage our body in activities, for example sucking, smiling, moving our hands to find our toes, rolling, sitting, holding a toy, we are creating proprioceptive signals. Some of these are responded to reflexively at the spine, brain stem or cerebellum level; other signals move further through the CNS creating body maps, held in the cerebellum and somatosensory cortex. These body maps are known as our homunculi (found in our somatosensory cortex, motor cortex and cerebellum).
For every part of our body, we hold a virtual body part in our brain. The size of the virtual map representation is down to the amount of proprioceptive and tactile information elicited from the body part. So usually, our virtual body has very large hands, face and lips and smaller legs and arms.
Interestingly our body memory map also has space for objects that we use often; they become like extensions of our body. We see this now with mobile phones.They have become an extension of us!
We start creating our virtual maps in the womb when we are held in fluid and an ever-tighter 3D space. The combination of these enables the baby to move initially quite freely without the force of gravity and then experience ever more proprioceptive signals as the baby pushes against the uterine wall. These weeks of proprioceptive experience are lost if born early when very few self-initiated movements are possible as there is no fluid to support movement and no boundaried 3D space to push and move against.
Competent movement requires good body maps! The more detailed the map the more we know ourselves and our capabilities and the more precise the movements we make. Without the detail, if we have gaps, our movements can appear ‘clumsy’ – a ‘move it or lose it’ principle. This is why we want to support active movements in the baby as soon as possible so the maps can be built, evolved and maintained.
Remember that reflexive movements in response to stress are not going to enable us to build libraries of helpful movement memories for future exploration and learning. On the other hand, attuned and playful movement experiences from a safe base are going to encourage exploration, experimentation and plentiful body maps.
In our next blog, we will discuss how proprioception protects, regulates, and discriminates.