The Tesla chief -- who also heads Neuralink -- posted a link from his company that featured about 9 minutes of video from Neuralink ... and it's a full-blown testimonial from a guy named Noland Arbaugh -- a 29-year-old quadriplegic who went under the knife for this.

He says he was in a freak diving accident about 8 years ago, and it left him paralyzed from the shoulders down. After hearing about what Neuralink could do, however, he signed up.

The clip goes on to show how exactly the technology works -- and sure enough ... you can see Noland using his mind to move a mouse around on a laptop that's set up in front of him ... on which the guy's playing chess. It looks pretty seamless, and he's got it down pat!

Noland is able to move chess pieces on the screen and even turn down music -- all by simply thinking about where he wants the mouse to go. He gets into the weeds a bit in describing how exactly he does it ... saying he's implementing something called imagined movement, trying to pivot away from attempted movement with a whole lot of brain power.

Like we said ... he certainly seems to have a knack for it now -- and even more amazing is how well he appears to be doing post-surgery, something else he touches on in this video.

Noland gives a ringing endorsement for Neuralink -- acknowledging there's still much work to do to perfect it ... but saying the progress they've made so far is promising. He says the number of people this could potentially help is staggering ... and he's happy to be patient #1.

It's pretty powerful visuals ... and you gotta imagine more folks are gonna put their names down to be guinea pigs for this effort -- especially seeing how well it's gone thus far.