How do we know where our body begins and ends?
We are remarkably good at working out where the various bits of our bodies are and moving them to where we want them to be. How can we manage to move parts of it so precisely?
This skill allows us to walk, talk, write, type and play tennis. Fortunately, we generally obtain this information automatically – we don’t need to see or touch our leg to know where it is.
Monitoring is carried out by a network of proprioceptors, sensory neurons in tissues such as muscle, tendon and ligament. These send messages to the cerebellum, which achieves the awesome task of integrating information to manage our posture. It also relays signals to the motor system in the cortex, feeding into control of movement.
Butterflies in your stomach?
But what is going on when we don’t feel well ‘in ourselves’? A slightly different (and less well-understood) concept is that of interoception – detection of internal states.
This inspection includes input from stretch receptors associated with organs such as the gut, but extends beyond that to a sense of how we ‘feel’ internally. Hunger, thirst, pain and similar sensations are all aspects of these subjective states.
There is a strong emotional component to these sensations – and, conversely, strong emotions can trigger sensations that suggest internal physical changes (“my heart was in my mouth”; “I was sick to the pit of my stomach”).
The interoceptive system is centred on a region of the brain known as the insula, and has been proposed to be responsible for producing an integrated sense of subjective ‘self’ (and hence may play a role in consciousness or self-awareness). Interestingly, the insula is thickened in people who meditate, a technique that emphasises concentration on internal body states.