When Herbert Simon and Allen Newell started their project of using computers to simulate human mental processes in problem solving in game play in 1960’, they did not know much about the real human mental processes in problem solving. This is true even now for us. My research is motivated to understand the human mental processes in problem solving using behaviroal, neuroimaging and neurophysiological approaches, with aims to reveal the underlying mechanisms of human rationality (the capability to think logically) and expertise (the capability to think unconsciously). I hope by these efforts it may discover the most efficient training methods fitting for individuals who motivate to become professional in their fields.