Einstein is widely regarded as one of the smartest people who has ever lived. In fact, if you were to ask random people on the street "who is the smartest human being (living or dead) you can name," I'd find it hard to believe if Einstein's name didn't make the top 3. When Einstein died, his brain was quickly removed (within 7.5 hours actually) and saved so it could be studied. neuroscientists wanted to know what made Einstein's brain tick - why was he so smart? In the end, the answer is both exciting and a little depressing.
As far as we can determine, structurally, there is nothing different about Einstein's brain. In fact, his brain could be considered average. Terence Hines, the author of the paper Neuromythology of Einstein's Brain, said that he found nothing special about the genius's brain. So, how does his brain differ from everyone else's? It doesn't.
Since the time of Einstein's death, people have tried to explain away Einstein's revolutionary intelligence as a feat of genetics; he just hit the jackpot. There have been several studies that claimed to find structural abnormalities in his brain, such as a famous study performed in 1985 that claimed Einstein had a much higher concentration of glial cells than the average brain (basically, a glia is any cell in the nervous system that isn't a neuron). Hines looked at this, and other studies preformed on Einstein's brain in an attempt to analyze them. He found fundamental issues with all of them (in the case of the 1985 experiment, Hines believes the results were the work of the "multiple-comparisons problem").
Hines goes a little further to say that there is a post hoc logical fallacy used by those who attempt to explain Einstein's intelligence by looking at his brain's structure. The smallest abnormality tends to get blown up and serves as an example of confirmation bias since researchers are looking for a reason for Einstein's brain to be special.
I said in the beginning that this result was both exciting and depressing. If Einstein's brain isn't special, it means that you process all of the same tools Einstein did when he rewrote physics. Take whatever lesson you want from that.