There was nothing special about Albert Einstein's brain.

Nothing that modern neuroscience can detect, anyway. This is the message of a provocative article by Pace University psychologist Terence Hines, just published in Brain and Cognition: Neuromythology of Einstein’s brain As Hines notes, the story of how Einstein's brain was preserved is well known. When the physicist died in 1955, his wish was to be cremated, but the pathologist who performed the autopsy decided to save his brain for science. Einstein's son Hans later gave his blessing to this fait accompli. Samples and photos of the brain were then made available to neuroscientists around the world, who hoped to discover the secret of the great man's genius. Many have claimed to have found it. But Hines isn't convinced. Some researchers, for instance, have used microscopy to examine Einstein's brain tissue on a histological (cellular) level. Most famous amongst these studies is Diamond et al, who in 1985 reported that Einstein's brain had a significantly higher proportion of glial cells than those of matched, normal control brains. However, Hines points out that this 'finding' may have been a textbook example of the multiple-comparisons problem:

Diamond et al. (1985) reported four different t-tests, each comparing Einstein’s brain to the brains of the controls. Only one of the four tests performed was significant at the .05 level. Although only the results of the neuron to glial cell ratios were reported by Diamond et al. (1985), the paper makes it clear that at least six other dependent measures were examined: (1) number of neurons, (2) total number of glial cells, (3) number of astrocytes, (4) number of oligodendrocytes, (5) neuron to astrocyte ratio and (6) neuron to oligodendrocyte ratio. Thus a total of seven different dependent measures were examined in four different brain areas for a total of 28 comparisons... one p less than 0.05 result out of 28 is not surprising.

Other histological studies followed from other researchers, but Hines says that they do not present a coherent picture of clear differences:

In summary the three histological studies of Einstein’s brain have, in spite of claims to the contrary, found essentially no differences between his brain and that of controls. This should not come as any great surprise. The brain is obviously an extremely complex structure... to believe that the analyses of one or a few tiny slices of a single brain could reveal anything related to the specific cognitive abilities of that brain is naïve.

He concludes by suggesting that all of the claimed discoveries might reflect confirmation bias on the part of the researchers, and he proposes a blinded 'Pepsi challenge'-type test to see whether the claimed differences are real or just wishful thinking:

Future studies need to use more rigorous methodologies... For example, qualified but blinded observers could be asked to distinguish between microscope slides of Einstein’s brain and average brains. If there are actual differences, such an experimental methodology would reveal them.

So much for histology. How about the size and shape of Einstein's brain as a whole - the neuroanatomy? Here, Hines says, the story is much the same. Various features of Einstein's brain structure have been held up as abnormal, but it is not clear whether these are unique to Einstein as opposed to just normal variants. Hines also criticizes the logic of trying to 'explain' Einstein's mind from his neuroanatomy, post hoc. In response to one recent attempt, Hines says

Falk et al comment on "the extraordinary expansion of the lateral part of Einstein’s left primary somatosensory and left primary motor cortices" the face and tongue areas. They say "In this context it is interesting that Einstein’s famously wrote that thinking entailed an association of images and feelings, and that, for him, the elements of thought were, not only visual, but also muscular" The fact that Einstein described his thinking in such a way is "interesting". But would anyone ever have taken that description of his thinking process and predicted that the motor cortex in his left hemisphere representing his face and tongue would be "extraordinarily expanded"? I think the answer is clearly "no". This type of post hoc ergo propter hoc reasoning pervades much of the interpretations of the cognitive correlates of the observed differences in Einstein’s brain.

I haven't studied the Einstein-brain literature in any detail, but I'm skeptical that a study with (effectively) a sample size of one can tell us much about the neurobiology of something as hard to define as genius. Terence Hines, incidentally, has a track record of pouring cold water on hot anatomical claims - for instance when, in 2001, he cast doubt on

the G-spot: a modern gynecological myth.

His psychological output includes papers with such interesting titles as National Hockey League players from North America are more violent than those from Europe and male entertainment award winners are older than female winners.

Hines, T. (2014). Neuromythology of Einstein’s brain Brain and Cognition, 88 , 21-25 DOI: 10.1016/j.bandc.2014.04.004