It may have been the stuff of science fiction, once. But startups around the world are already running clinical trials based around brain implants that could one day treat such life-threatening conditions as brain cancer, chronic pain, rheumatoid arthritis, Parkinson’s disease, incontinence, and tinnitus. The Observer reports that it’s a billion-dollar industry, expected to be worth nearly $20 billion by the 2030s. The news follows a spate of sci-fi-worthy medical advances, such as this groundbreaking melanoma jab that uses AI to personalize cancer vaccines, and a recent study into the power o…