Have you heard of the Buffalo Theory?
It makes plenty of sense, here it is:

A herd of buffalo can move only as fast as the slowest buffalo. When the herd is hunted, it is the slowest and the weakest ones at the back that are killed first. This natural selection is good for the herd as whole, because the general speed and health of the whole group keeps improving by the regular culling of the weakest members.

In much the same way, the human brain can only operate as fast as its slowest brain cells. Excessive intake of alcohol kills brain cells. And, naturally, the slowest and weakest brain cells are attacked first.

And so, it can be hypothesized that regular consumption of beer eliminates the weaker brain cells, resulting in a faster and more efficient brain.

Hence, the reason to why you always feel smarter after a few beers!