The goal of experimental psychology from its outset has been to take the wondrous acts of human cognition and decompose them into their basic steps and understand how these steps are put together. For much of its history, psychology has been limited to observations of what went into the mind and what came out. Theoretical endeavors over the generations have built ever more complex models to account for the input-output relationships. Brain imaging offers the possibility of gathering signs from the processes that intervene between input and output. I will describe how we have combined complex models like ACT-R with such signs (tire tracks in the case of fMRI, a breadcrumb trail in the case of EEG) to understand the sequential structure of thought.