Do jellyfish sleep?

I like “quoughts” (questions that provoke thoughts) and “Do jellyfish sleep?” is a good one. Jellyfish are interesting for lots of reasons, one of them being their place on the evolutionary landscape. The first jellyfish-like creatures (the ancestors of modern jellyfish) pitched up during the Cambrian explosion, more than 500 million years ago and are one of the first animal groups to boast organised tissues and a nervous system. There is nothing that could be described as a brain, but jellyfish neurons work in exactly the same way as vertebrate neurons. So do jellyfish experience anything akin to vertebrate sleep?

Deep sleep, brain magnets and memory

Deep non-REM sleep appears to affect how well we commit a new task to memory Sleep specialists like to divide sleep into one of two states: rapid eye movement sleep (REM) and non-rapid eye movement sleep (non-REM). Since the discovery of REM and its tight link to dreaming in 1953, there has been a lot of research focused on this paradoxical wake-like state. But as we experience much more non-REM than REM during the night, non-REM or deep sleep might be the more important of the two states. It’s likely there are many functions of non-REM. It could simply be

The horrors of sleep deprivation

The definitive demonstration of the horrors of sleep deprivation appeared in a celebrated paper published by sleep research pioneer Allan Rechtschaffen and his colleagues in Science in 1983. They used rats. What nobody had managed until then was to design a set-up in which both experimental and control animals received exactly the same conditions but different amounts of sleep. The solution Rechtschaffen and co. came up with is as ingenious as it is disturbing. They installed a pair of rats in neighbouring cages. In the bottom of each cage was 3cm of water, but by standing on a record-player-like disk