What is brain controlled?
It's replacing the physical flight controls with directly brain-controlled flight controls. As to why: a large part of learning to fly (not the biggest part, certainly, but a significant piece) is learning how to use the fairly complicated controls. If you can simplify or even remove that interface, it makes the process of flying easier to learn.
Since this is Slashdot, someone is undoubtedly going to say that that learning difficulty is a good thing, since it sets a higher bar for pilots. There may be a bit of truth to that, but it's an artificial boundary that doesn't actually pertain to flying ability. It's like having to learn to use a Dvorak layout before you let anyone code: learning Dvorak probably won't make you a better coder, it'll simply make learning to code a more difficult process. Likewise, the complex controls that planes have doesn't make pilots better at flying, it simply makes learning to fly more difficult. So, while complicated controls might keep out lazy pilots, it won't keep out bad pilots (that's what the licensing requirements are for).