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When it comes to the human brain, even the simplest of acts can be counter-intuitive and deceptively complicated. For example, try stretching your arm.

Nerves in the limb send messages back to your brain, but the subjective experience you have of stretching isn't due to these signals.

The feeling that you willed your arm into motion, and the realisation that you moved it at all, are both the result of an area at the back of your brain called the posterior parietal cortex.

Dualist philosophers like Descartes believed that the mind and consciousness exist outside the physical world, producing our actions by interacting with the physical meat of our brains. The idea has become commonplace, but it's challenged by neuroscientific studies like this one, which show that the conscious intention to move emerges from electrical activity in neurons, tangible objects that are all too real.