One of Hume's most interesting insights rests on the idea that when it comes to the relationship between mind and body, our experience is merely of their constant conjunction, but never of any necessary connection between them. In other words, you experience that your body does what you tell it to, but you don't actually experience why. You assume that one causes the other to act, but that's ultimately just an inference you make, not something you actually experience.
And as with most things Hume, it's taken a few centuries to scientifically test these observations, but once again it looks like the man was on the right track. Some of the latest research has reached similar conclusions, and has provided valuable lessons about how our brain integrates and constructs its experience of its own body, and the findings are absolutely fascinating: for instance, you can be fooled into experiencing that a rubber hand that you 'know' isn't yours is yours :)
Here is a more concise explanation of what's going on:
And because scientists are not doing this just for shits and giggles, here is an important example of a possible application of this research:
This could provide more confirmation of the natural basis for out-of-body experiences, wouldn't it?