A new phase of research on teaching is under way that seeks to understand the teaching brain. In this vein, this study investigated the cognitive processes employed by master teachers. Using an interview protocol influenced by microgenetic techniques, 23 master teachers used the Self-in-Relation-to-Teaching (SiR2T) tool to answer "What are you focusing your mind on throughout the process of teaching?" A number of emergent themes were identified in participants' responses and one, awareness of interaction, is discussed here. This theme refers to teachers' recognition of the learner-teacher (L-T) relationship as a separate entity or system. Within interaction, at least three types of awarenesses emerged in teachers' responses: (1) connection, (2) collaboration, and (3) mutual effects. Furthermore, some teachers described a sense of synergy with their students due to this L-T interaction. The results suggest that a teacher's awareness of interaction plays an important role in the teaching brain, and support the implications of the proposed teaching brain framework.