Seconds after a brief smile of anticipation flashed across her face, Jan Scheuermann moved a bar of chocolate toward her mouth by controlling a robotic prosthetic arm. Finally, she took a bite. As she relished the taste, the team of neuroscientists and engineers in the room erupted in applause. It was no small feat for Scheuermann to feed herself. Fourteen years before this 2012 experiment, she had been diagnosed with spinocerebellar ataxia, which causes progressive and irreversible paralysis. In the intervening years, she had gradually lost the ability to move her arms and legs.