Do you remember playing pretend when you were a child? A stick became a sword while a playground became a castle. This ability to use your imagination doesn't disappear after childhood, though; it persists when people create art, invent tools and think scientifically. Now, scientists have discovered the source of human imagination.

In the past, researchers have theorized that the human imagination requires a widespread neural network in the brain. Evidence for such a "mental workspace," though, has been difficult to produce with techniques that mainly study brain activity in isolation. In order to overcome that issue, the researchers decided to focus on how the brain allows us to manipulate mental imagery. An example would be imagining a stick to be a sword, or imagining a honeybee with butterfly wings.

In their study, the researchers asked 15 participants to imagine specific abstract visual shapes and to mentally combine them into more complex figures or to mentally dismantle them into their separate parts. The scientists then measured the participants' brain activity with functional MRI.

So what did they find? It turns out that a cortical and subcortical network over a large part of the brain was responsible for the imagery manipulations. This network closely resembled the "mental workspace" that scientists theorized might be responsible for imagination.

"Our findings move us closer to understanding how the organization of our brains sets us apart from other species and provides such a rich internal playground for us to think freely and creatively," said Alex Schlegel, the lead author of the paper, in a news release. "Understanding these differences will give us insight into where human creativity comes from and possibly allow us to recreate those same creative processes in machines."

The findings are important for understanding exactly how our brains process imagery and work with complex problems. It also reveals that this mental workspace actually exists, which could have important implications for future research.

The findings are published in the journal Proceedings of the National Academy of Sciences.