how to make arduino as mind thought reader?
Even if the answer provided by Mike is really doable and can be implemented you should really think about what you want to reach and what is your goal.

The big difference between EEG and mind readers is that the process of thinking, even if you can record all that waves: alpha, gamma,... can be never decoded to get useful informations. I mean: you can record and get a confirm that you have more gamma waves when you are doing meditation. Or that aplha and beta wave are going to be much more present when waking up or in particular hours of the days, but you never get an image of what the person is thinking or what are its emotions... That because you can get some waves coming from the brain but you cannot reconstruct the billion of processes that are happening inside the brain.

A lot of researcher are trying to decoder those informations to move as an example an arm or a leg. But it is the front edge of the reasearch really not doable with an Arduino....

Anyway good luck!