Have you ever wondered why you can’t tickle yourself? It’s due to a mechanism called ‘sensory suppression’ and the phenomena serves as a reminder for us to keep our treatments as ‘active’ as possible at every stage of rehabilitation.
Why you can’t tickle yourself
When we are tickled by another person the quality and intensity of the sensory experience is much greater than when we try and tickle ourselves. It’s a fascinating phenomena isn’t it, but why is this the case?
When we self-initiate movements the afferent information generated – such as sensory impulses from the skin or proprioceptive impulses from muscle spindles – doesn’t reach consciousness; there is partial suppression of the afferent activity.
This phenomena allows us to concentrate upon external stimuli in our day to day lives whilst at the same time being less preoccupied by the sensations arising from our own movements. (Although interestingly this does not appear to be the case in schizophrenia. See Blakemore et al 2000).
I guess our physical lives would very quickly descend into chaos if we were as conscious of the sensations arising from our own self-initiated movements as we are of external stimuli in equal measure.
Clinical implications
So, what does all this mean for our clinical work?
Proske and Gandevia (2012) have presented evidence demonstrating that subjects will overestimate an external compression force applied to the hand by an experimental apparatus, when asked to reproduce the felt force using their opposite hand. Loosely put, the external forces are ‘felt more’.
Extrapolating this to clinical work suggests that when we are moving a persons body passively ‘for them’, then the forces and sensations generated will be perceived as greater and more intense, than the same movement self-generated and performed by themselves.
It’s one more reason to keep treatment active and self generated and to keep away as much as possible from passive approaches that are ‘done to’ people.
Don’t you wish you were taught this kind of stuff as an undergraduate?!
References
Blakemore SJ et al 2000 Why can’t you tickle yourself? NeuroReport 11:11-16
(Proske & Gandevia’s 2012 review is breathtaking. One of those rare review papers that is entertaining yet at the same time both readable and erudite. I must have spent three weeks pouring over the paper when I first read it. Thoroughly recommended read. Full text available above. Enjoy!).