Yes I feel it, I only assumed myself being as a youngster speaking with one of my friends in the same age, you know all about those words in that age?!
"at the same time" is OK, but you have it in the wrong place. You can say this:
"... the most simple and at the same time upgradable apparatus ..."
I am not totally convinced about the statement as a whole. Is the brain "simple" or "upgradable"? The verb "reinforce" may also not be the best choice. I am not very clear what to suggest in its place though.
Thanks for the response GPY. Well, You're right. "simple" is not a wise choice. Maybe "ubiquitous" and "available" were better. but about "reinforce", I have no idea. how about "improve"...? Um..., thanks anyway.