Imagination

The experiments of neuronal activity in rodents are important, experts say, because they place the idea of imagination into a physical reality: that of the brain itself. 

“This gives us an opportunity to take a fuzzy cognitive concept like imagination” and link it to brain activity, says Daphna Shohamy, a cognitive neuroscientist at Columbia University, and director and CEO of Columbia's Zuckerman Institute, who was not involved in those studies or the review paper.

Humans’ internal worlds are rich, however, and the studies of place cells in rats may not represent all types of human imagination. The animal results connect most directly with imagination that is based in experience and action, as in planning out a strategy for moving through the world, Nadel says. 

But other experts believe the hippocampus has a much broader repertoire: it may also forge ties between ideas and information. 

“I don’t think the hippocampus cares, really, about what you’re connecting,” Addis says.

Some of Shohamy’s work supports the idea that the hippocampus might be important for mental simulations that are not rooted in time or place. 

She has found that people with damage to the hippocampus are much slower than those without brain damage to choose between food items —say, a Kit Kat versus M&Ms —that they like about equally well.