Which is why it will be a facsimile AI...or in the shorter term, you'll see stuff like "jacking in" from cyberpunk or Matrix...think of AI as "buffers" to the storage of the brain...there are theoretical limits to the computer ability to process info beyond that, but they are immensely high.
I don't think you actually read the article I linked to, or if you did, you missed the point. What the research shows is that, yes, you could increase the brain's ability to do a certain thing, but there are negative consequences to that increase that might cancel out any benefits from it. Amplify a person's imagination too much and they become schizophrenic. Amplify their logic and systematic thought too much and they become autistic. Amplify their ability to discern patterns too much and they become paranoid. By analogy, you could engineer the body to have extra limbs or sense organs or muscles, but the added metabolic cost of having them might cancel out any gain from having them, or the amount of neurological connections that would have to be devoted to them might diminish one's mental or physical functionality. So there are limits to how much you can practically enhance a body's physical abilities, and the same may well be true for enhancing a brain.
So even if you did use external computer hardware to enhance the brain's performance, it might end up undermining the brain's performance in key ways as well, throwing off the balance that enables it to work. Human intelligence may already be at the point of diminishing returns -- or, to put it more optimistically, in a sort of "Goldilocks zone" for sentience, an optimal balance where our minds have enough complexity and dynamism to be conscious and creative but not so much that they become unstable.