Many would say the Mind – but the mental body has no material existence and so has no direct sensory/physical input. Some would say the brain – and it does help!
But your entire physical being is needed because your body has the only complete and accurate recordings of all your life experiences.
Imagination grows from your genetic endowment and your adaptive learnings and is often sparked from the heart because it can be both the receiver and transmitter of our spiritual yearnings.
Best we treat it accordingly…