Move around a little as you read this -- wave your arm, wiggle your ears, lift a foot, whatever. Did you feel the movement of the part you chose to move? Almost certainly. But how did you know you were moving that part? Believe it or not, that's a question that has puzzled scientists for over a century.

Where does the sense of movement live? Is it in the receptors in the joints or muscles, in the brain itself, or somewhere in between in the nervous tissues? Maybe a combination of all of these?

A small study in Australia suggests that merely the intention to move can produce a sensation of real movement -- even when real movement isn't even possible.

(Simon) Gandevia's (of the Prince of Wales Medical Research Institute in Sydney, Australia) team studied eight volunteers, by either anaesthetising their forearm and hand, or restricting the flow of blood to the limb. Both techniques deadened sensation to the extent that the volunteers felt they had a "phantom" hand with fingers clenched, though in fact their fingers were fully extended. When they were asked to flex or extend their wrists, they consistently reported that the position of their hand had changed, in the direction of their efforts, even though it did not move. When they were asked to increase their efforts, the perceived change also increased.

The relationship between sensing and moving seems commonsense. But, here in this limited study, it seems both the sensing and moving are illusions, though the experience of intended movement makes a apparent appearance. Perhaps this is an instance of plasticity at work -- rapid experience-based changes in the nervous system, but fueled by thought alone.

This is not unlike phantom limb sensations that can bother amputees. But it kind of surprises me that it can happen so rapidly in those who aren't amputees.