Researchers have been poking and prodding the brain with electricity for years. Cochlear implants are used to restore hearing and speech in people who are deaf and experimental research has demonstrated prosthetic limbs being controlled with thoughts. But ears perked when Elon Musk recently announced he was going to put his intellectual and financial heft behind a new venture that aims to wire computers to the brain to treat injuries and disease that affect movement. Soon after, Facebook put out its own call for brain-machine interface engineers.

At the simplest level, the brain does this: data comes in — fast and furious from our environment — and data comes out, ever so slowly and limited essentially by how fast we can talk or type. In between, electrical impulses carry information between neurons. We know a fair bit about how that happens and when it goes wrong, but there is a lot that is unknown. The big question is what we can do with what we know and what we might learn along the way.

Brain-machine interfaces are having a moment. We asked four scientists whether it is the moment and what we can reasonably expect from the intersection of engineering and neuroscience:

• Sridevi Sarma, biomedical engineer, Johns Hopkins University: How and how much to change the brain
• Steven Chase, biomedical engineer, Carnegie Mellon University: What to fear
• Andrew Hires, neurobiologist, University of Southern California: An optical link to the brain
• Sliman Bensmaia, neurobiologist, University of Chicago: The internet inside your mind