It is proposed by Eccles that (1) The mental world consists of mental units called psychons; (2) The brain world consists of nerve units called dendrons; (3) In mind-brain interaction, psychons and dendrons are linked through quantum physics. In this note, we formalize the above ideas. Emotions are represented by emotion state vectors. The motion of emotion (emotion state vector) depends on the previous psychon state vector, the previous emotion and brain state. The brain state is in turn stimulated by outside stimuli and influenced by psychon state vectors. In this paper, we specify the mind-brain interaction by several operators. A complete theory is presented in this paper.