This study examines the role of simulation in explaining brain phenomena. The notions of simulation analyzed here are diverse: A computer simulation of specific brain phenomena, a researcher's mental simulation of a brain process or an experimental setting as a simulation of a natural situation. The objective of this study is to clarify the various roles that simulation plays in explanations of brain phenomena and to ask whether there is one generic notion of simulation that reconciles the various roles. It is argued that the main reason for simulation being massively deployed for explanations of the brain is the dynamics and complexity of the brain itself. Further, the common ground for the diverse notions of simulation is the result of a characteristic set of models and representations that underlies practical scientific work, in the brain sciences (and elsewhere). It is concluded that - contrary to the common notion that simulation is somewhere outside in a computer or some other device - most of it is inside our head. Explaining brains by simulation is primarily done by our brains.