Brad Carter’s face is immediately familiar: the character actor has appeared in scores of shows, including Sons of Anarchy, True Detective and CSI. But his role in 2013 made history: he was the star of a live surgical procedure on Twitter. Instagram photos, tweets and six-second videos documented a UCLA medical team implanting a brain pacemaker while millions watched. At a critical point in the surgery, Carter was awakened to strum his guitar so the team could properly position electrodes.Carter suffers from a condition known as essential tremors, which had effectively taken away his music. After the surgery, Carter’s hands regained much of their dexterity. And an entirely new audience had learned about surgical options for tremors. “It feels bigger than me,” Carter says of his brain surgery/social media experience.