All desires come from memory. Creativity is almost impossible without solid memories of the past. The mental function that has the deepest correlation with memory is emotion. But what else are those feelings based on, memories. Memories shape our emotions. So, you have to have a lot of memories to create a desire to do something.
So memory is desire. All memories are currently happening in brain science. Memories are stored in the past, but the act of recalling them becomes the present. If not recalled, the memory is lost. It's different every time because it's based on how I feel when I recall it. It then reconstructs the memory according to its brain state.