Research on the human brain, the external brain and the public external brain

Information technology such as Internet, Internet of Things and mobile communication is the infrastructure of information communication under network digital space. With increasingly completion of information technology, people can instantly access and get information in digital network space. The cognition and learning of the human brain can achieve real-time synchronization with cyberspace. Digital cyberspace is like an external brain and a public external brain, and they are part of human brain's memory and thinking. This paper defines the human brain, the external brain and the public external brain, and summarizes attributes and relationships of the three, moreover proposes human cognition and action models in the digital age to understand human behavior. This model provides an engineering cognitive perspective and thinking method for understanding human behavior and social activities in the digital age.