Please read the article of "Computer modelling: Brain in a box" by Mitchell Waldrop as a part of the Nature feature on Alan Turing.
"The article describes what it will take to model the human brain and the sceptics view of the project. I have little doubt that modelling the human brain is possible. The fact that nature can encode the brain's development and function using a triplet coding system (DNA) I see no reason why we cannot do it using binary code in a computer. Judge for yourselves."