neuroprosthesis
A neuroprosthesis is a device that connects to the nervous system to take over a function the body has lost. It either reads signals from the brain or nerves to do something useful, or sends signals in to make up for a sense that is missing. Either way, it is a bridge between living tissue and a machine.
Some neuroprostheses listen. A robotic arm controlled by a paralyzed person's motor signals is reading the brain's intentions and turning them into movement. Others talk. A cochlear implant turns sound into electrical pulses that stimulate the hearing nerve, and a retinal implant feeds light patterns into the eye's remaining cells.
The dream behind all of them is the same: when a natural pathway is broken, build a new one out of electrodes and software. The challenge is doing it so smoothly that the device starts to feel less like a tool and more like part of the person.
Not every neuroprosthesis is a brain–computer interface — a cochlear implant works on a nerve, not the brain — but the two families overlap heavily and share the same core idea.