They are just implanting stuff into you.

There are already working implants, like pacemakers, this is just more complicated.

They have to figure out how to do it without causing too much side effects.

https://en.wikipedia.org/wiki/Deep_brain_stimulation

They're used to excite brain areas, with some success in granting euphoria to depressed patients, as detailed here:

https://www.theatlantic.com/health/archive/2018/03/pleasure-...

Neuralink's main innovation is its aim in making the brain implant able to transmit information outward, for use in prosthetics, and yes, mind-to-machine input. The last is what he's going for, allowing us to bypass text-input/voice-input or gesture in favor of directly thinking them. We'll see how much of that aim is able to be done or not, with our current technology.