Nothing good ever starts with the line "Stick out your arm for science", unless you happen to be hanging out with Greg Gage, a neuroscientist-turned-science communicator dedicated to teaching young people about how the brain works. And what better way to do that, than by taking over control of one of their limbs, as you can see demonstrated in the creepy TED demonstration above.
At the heart of this experiment is some pretty simple neuroscience - when we tell our hands to move, our brains send electrical signals through our spinal cords and out into nerves that run through our arms. And once we learn how to read those electrical impulses, we can hijack them.
In the experiment above, Gage tries this out on two unsuspecting victims - who have all my respect, by the way. I can't say I'd be too willing to let someone stick electrodes on me in the name of science without seeing ethics approval first. To get started, Gage 'reads' the electrical signals that volunteer Sam's brain puts out when she moves her hand.
He then straps some electrodes onto the arm of a second volunteer, Miguel, and, after a little tuning, all Sam has to do is think about moving her hand, and Miguel's arm starts to jump and twitch like some kind of possessed zombie limb. (Fun fact here: the nerve that controls your hand movements is close enough to the skin that it can be stimulated non-invasively.) It's eerie and fascinating all at the same time.
The best (or worst?) part is that you can actually try this kind of stuff at home, thanks to Gage's company, Backyard Brains, which makes cheap and easy-to-use neuroscience equipment for people to play around with. Word of warning though, mind control can have some unpleasant side effects. According to Gage: "When you lose your free will and someone else becomes your agent it does feel a bit strange." Don't worry, we believe you.