Sleep scoring in rodents: criteria, automatic approaches and outstanding issues.

There is nothing we spend as much time on in our lives as we do on sleep. Which makes it even more surprising that we currently do not know why we need to sleep. Most of the research addressing this question is performed in rodents to allow for invasive, mechanistic approaches. However, in contrast to human sleep, we currently do not have shared, agreed-upon standards on sleep states in rodents. In this article we present an overview on sleep stages in humans and rodents, and a historical perspective on the development of automatic sleep scoring systems in rodents. Further, we highlight specific issues in rodent sleep that also call into question some of the standards used in human sleep research.