I have seen this chap before but the performance continues to dazzle and astound.
Where he admits to at times using mnemonics to act as proxies for large numbers
seems to be a common technique used by people that perform these type of
mental feats, such as those who can memorize the order of a deck of shuffled
cards. It probably gives some clue into how our brains organize and store
information.
I would not be surprised if gram for gram, the weight of these people's brains
is probably no different to the rest of us and it makes one wonder if the
difference between what we regard as average and what we regard as genius turns
out to be just a very small difference in some of the wiring. Perhaps one day
we will know.