A dream can sometimes stay with us all day, perhaps even longer. Other times we wake up and don't really remember much of what we've dreamed about. But what about other animals? Do they dream? It's a question we'll perhaps never be able to answer — but let's give it a shot.
The logo for the International Institute for Integrative Sleep Medicine (IIIS) in Tsukuba, Ibaraki Prefecture, is a sleepy cartoon mouse curled up next to our planet. It is apt in two ways. First, while sleep is familiar to everyone in the world — and indeed to all animals — there is still a lot we don't know about it. Second, the institute, based at the University of Tsukuba, aims to solve this mystery by using mice.
We spend approximately a third of our lives asleep, but exactly what sleep does for us is a mystery. Scientists assume there is something that builds up during our waking hours that makes us gradually more sleepy. If there is such a substance, however, we don't know what it is.