Neuroscientist Greg Gage demonstrates how one person’s brain can be used to control another person’s arm. Gage uses cheap equipment to read the nerve impulses from his one person. He then can relay those impulses through a “human-to-human interface” into the arm of another person. Once the setup is properly configured, whenever the first person moves her hand it causes the other hand to move involuntarily. The video demonstrates the interface in detail, including construction info for the device.
And this is his recent TED Talk: