Lovecraft might have liked this new paper by Frank and colleagues, since he though squid-like beings could dream...
In his house at R’lyeh, dead Cthulu waits dreaming.
Sleep is a surprisingly thorny behaviour to explain. Why should an animal stop attending the world around them (or, to put it in human terms, losing consciousness), leaving itself vulnerable to how knows how many shocks and threats?
Research on human sleep has defined and driven sleep research. The question of invertebrate sleep, for example, was very slow to develop because of the problems in comparing invertebrate neurophysiology to vertebrate neurophysiology. Research on human sleep had been revolutionized by the Hans Berger’s introduction of electroencephalography (EEG), which allowed us to see the differences in brainwaves during sleep. EEGs defined sleep research so much that one researcher I know was told that she could not say an invertebrate was sleeping because there were no records of brain waves, regardless of what the behaviour was.
Cephalopods are potentially very interesting subjects for sleep research because of their brainwaves. When you try to record brainwaves from most invertebrates, you get very spiky recordings rather than waves. Cephalopods, and particularly octopuses, have brain waves that are more vertebrate like: wavy, not spiky (Ted Bullock wrote about this quote a bit). So for those who define sleep by changes in brain wave activity, cephalopods may offer more points of comparison.
This new paper by Frank and company doesn’t have brainwaves, but could be an important first step in developing methods to study sleep in cephs. They do two things here.
First, they document that cuttlefish go through periods of behavioural sleep: prolonged inactivity. They call this an experiment, but there isn’t any manipulation, so it’s really just a study. They do document some intermittent behaviours that they argue are analogous to rapid eye movement (REM) sleep in mammals, though I don’t buy that at all.
The second experiment is much more interesting. I’m sure everyone has had the experience when you don’t get enough sleep. When you’ve been deprived of sleep, the next time you do sleep, you sleep more than normal. That “rebound” is evidence that the inactive state is sleep and not just inactivity.
So Frank and company sleep deprived their cuttlefish. Now, sleep depriving an animal is a very tricky business. How do you stop a cuttlefish from sleeping?
This was one of those rare times I was glad I read the methods section.
Hans Zimmer’s “King Arthur” film score (2004) was played (Microsoft’s Window Media Player) and the visualizer option was used to project random shapes on the screen. Angled mirrors placed around the sides of the tank reflected the screen image all around the cuttlefish to ensure constant, gently moving visual stimulation.
That’s... oddly specific.
Regardless of their choice of film scores, Frank and company did indeed find that after being prevented from “sleep,” their cuttlefish did indeed sleep more when next given the chance.
This is a very cool and promising start on sleep research in cephs. But I’ll tell the authors this for free: if you want to push this further and catch the attention of mainstream sleep researchers, you’re going to have to record brain activity. It will be maddeningly hard, but if you can get those data, that’s when things will start to get fun.
Additional, 23 June: I have an answer to the question I posed in the title!
Frank MG, Waldrop RH, Dumoulin M, Aton S, Boal JG. 2012. A preliminary analysis of sleep-like states in the cuttlefish Sepia officinalis. PLoS ONE 7(6): e38125. DOI: 10.1371/journal.pone.0038125
Cuttlefish photo by Eric Burgers on Flickr; used under a Creative Commons license.