Do jellyfish sleep?

I like “quoughts” (questions that provoke thoughts) and “Do jellyfish sleep?” is a good one.

Exceptionally preserved, but mini, jellyfish from the Middle Cambrian. The scale bar is just 5mm.

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?

The box jellyfish Chironex fleckeri is a species infamous for its lethal sting. They are active predators and are extremely mobile during the hours of daylight, typically covering around 200 metres an hour. At night, however, they basically stop moving altogether. ‘During these periods of “inactivity”, the jellyfish lie motionless on the sea floor, with no bell pulsation occurring and with tentacles completely relaxed and in contact with the sea floor,’ wrote Jamie Seymour and colleagues in the Medical Journal of Australia back in 2004. A small disturbance – like a light or a vibration – ‘causes the animals to rise from the sea floor, swim around for a short period, and then fall back into an inactive state on the sand.’ To Seymour and his colleagues, this looked a lot like sleep.

What is particularly interesting about the box jellyfish is that it has four sets of six eyes (so 24 in total), some of them endowed with lenses and retinas and are clearly capable of forming images. Perhaps these structures, which require huge neurological processing, set the stage for the emergence of two distinct states of vigilance. One – wakefulness – allowed the animal to focus on the analysis of complex visual information and the split-second making of decisions. The other – sleep – became the brain’s opportunity to process information without being overloaded by the senses. It’s an idea put forward by evolutionary biologist Lee Kavanau in the 1990s.

In 2017, researchers (writing in Current Biology) addressed the question of whether jellyfish sleep in a more robust manner. Working with the upside-down jellyfish of the genus Cassiopea in a laboratory setting, they used cameras to extract information on pulsing activity and found the jellyfish much less active during the hours of darkness. When released into a water column during hours of light, the jellyfish were pretty quick to pulse (within 2s). In darkness, however, it took them much longer to respond to the disturbance (around 6s). It was almost as if they’d been sleeping.

If the intervention had indeed “woken” the animals from a kip, the researchers predicted they would be quicker to respond to another whoosh through the water just 30s later. This turned out to be the case, from which we can infer that a jellyfish – unceremoniously disturbed from its night-time slumber – takes more than 30s to fall back asleep. A further experiment showed that when deprived of rest (by regularly mixing the water column), the jellyfish catch up on it as soon as they can, strongly suggesting it’s possible to sleep-deprive a jellyfish. Unkind perhaps, but interesting.

There are so many similarities between jellyfish sleep and that of vertebrates – at a molecular, physiological and behavioural level – it looks like sleep may only have evolved once, being modified through natural selection to meet the behavioural and ecological needs of those species that came later.

In most vertebrates, including humans, sleep is now thought to bring many benefits, allowing the strengthening of some synapses, the paring back of others, the replenishment of neurotransmitters, the removal of toxins, repair of ware and tare and energy saving. I think we can conclude that jellyfish do sleep or something very like it. What will be really interesting is to study the variation in this behaviour in different lineages of jellyfish, as this might shed light on what benefits this quiescence brought to the most primitive jellyfish way back in the mists of evolutionary time.

Donald Trump, basketball and the dangers of late-night tweeting

Voice of America

Donald Trump is famous for his late-night tweeting. Does this pattern of behaviour reduce his ability to perform during the day?

He might be interested in research presented yesterday at the Sleep 2017 conference in Boston showing a correlation between late-night tweeting and the next-day game performance of professional basketball players.

Over the course of six years, from 2009-2016, researchers drew data from the Twitter accounts of 90 National Basketball Association (NBA) players. In particular, they were interested in any athletes who made tweets between 11pm and 7am on the night before the game.

On average, late-night tweeters scored fewer points per game (8.2 versus 9.2 for non-tweeters), a lower shooting success for both field goals (36% compared to 41%) and free throws (39% against 44%). In games where a player had not been tweeting, they had a 1.7% increase in shooting accuracy compared to games where they had been on Twitter the night before.

“Our findings are relevant beyond just sports science research,” says Lauren Hale, professor of family, population and preventive medicine in the Program in Public Health at Stony Brook University. “Our results demonstrate a broader phenomenon: to perform at your personal best, you should get a full night of sleep.”

This study meshes into a wider literature on the impact of addictive screen-based devices on the quality and quantity of sleep. A statistic I still can’t get my head around is that one in three babies in America have a TV in their bedroom by the age of one and spend almost two hours in front of a screen every day. By the age of eight, these figures have swollen, so that almost half of young children in the US have a TV in their room. These figures come from a study published in 2011, so lord knows what they are now. They will only have gone up.

In the UK, children typically consume an average of over six hours of screen-based media every day. In the US, it’s probably more like seven and a half hours. In Canada it’s nearly eight. In essence, children in the developed world are spending more than half their waking lives in front of a screen.

The impact of screens on sleep is not just a problem for young children and adolescents. In adults too, more screen time tends to result in less sleep, either eating into the amount of time available for kipping or, perhaps by interfering with circadian rhythm, disrupting its quality.

Measuring performance of basketball players is relatively straight-forward but someone now needs to carry out the same analysis on Donald Trump. There are several obvious next-day metrics that might be used to correlate with the President’s late-night tweeting: frequency of using the words “the wall”, “travel ban”, “lock her up”; probability of having a run-in with the security services, insulting a foreign leader or dignitary; number of GBU-43/B Massive Ordnance Air Blast’s dropped or, perhaps, vaginas clutched at per hour.

While I look for the funding to get the analysis started, please leave any further suggestions in the comments.

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 a means of energy saving, reducing metabolic output during naturally selected hours of inactivity. Non-REM could involve some kind of neurological reset, allowing the neurons to replenish neurotransmitters. Perhaps the downtime is used to clear metabolites. There may be synaptic strengthening. There may be synaptic pruning. Both of these could enhance brain performance. It’s possible that non-REM performs all of these functions, and more besides.

There is an interesting experimental study on non-REM in Nature Communications this week. Researchers in Switzerland gave volunteers the task of learning a specific sequence of six finger taps, rather like asking them to learn to play a six-note ditty on the piano with the fingers of one hand but without the sound. After learning, as the subjects slept, some received a pulse of “transcranial magnetic stimulation” (TMS) directed at their motor cortex and timed to coincide with the deep, non-REM state. Although these experimental individuals didn’t notice they’d been targeted during the night and reported sleeping just as well as controls, they did less well at the six-finger memory task when tested the following day.

It’s a small study, but it does suggest that targeted TMS could be a useful experimental tool in efforts to figure out what is going on in the different stages of sleep. There is a therapeutic flip-side too. TMS is increasingly deployed for the treatment of depression and, appropriately delivered, might be able to enhance rather than disrupt non-REM sleep, thereby improving learning and memory (see this study, for instance).

In the last sentence, the words “appropriately delivered” are fairly important because I can see the growth of a poorly evidenced TMS industry, with desperate sleep-disordered people donning magnets at night and synching them with beautiful apps that promise stimulation at just the right frequency at just the right moment.

This would be about as silly as trying to run before walking. Sleep science is still in its infancy and it would seem wise to get a better handle on what is happening in our brains when we sleep before we begin self-medicating with magnets.

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 shared by both cages the rats were able to stay high and dry. The brains of both animals were wired up to an electroencephalogram (EEG) to record patterns of wake and sleep. Cleverly, the record player was controlled by the brain waves of the experimental rat. As soon as it fell asleep, the disk began to rotate at a leisurely 3.5 rpm.

“Whenever the disk was rotated, both rats had to walk in the direction opposite to the disk rotation to avoid being forced into the water,” wrote Rechtschaffen et al. So the animals were subject to the same environment and rotation, made to walk an average of almost one mile a day, but got very different amounts of sleep. Experimental rats got almost none, whilst control rats were able to grab some rest when the experimental rats were spontaneously awake and the turntable was stationary. “This study is best viewed as a comparison between severe and moderate sleep deprivation,” they wrote.

With time, the severely sleep deprived rats began to deteriorate, showing at least two of several pathological signs, including ungroomed fur, skin lesions, swollen paws, inability to move, loss of balance and significant weakening of the EEG signal. Three of eight experimental rats died, one after just five days. When Rechtschaffen and co. carried out necropsies on the deceased they found evidence of further problems, including collapsed lung, stomach ulcers, internal bleeding, testicular atrophy, severe scrotal damage and swollen bladder. The control rats, by contrast, were in relatively good nick.

The conclusion: “Sleep does serve a vital physiological function.”

Gessner’s bear

Historia animalium by Conrad Gesner, Henry Nicholls
De urso, from Conrad Gesner’s Historia Animalium

Last month, I hosted a post by historian Florike Egmond on my Guardian blog Animal Magic, one that proved incredibly popular.

A few years ago, Egmond was in the Amsterdam University Library when she discovered an amazing collection of 16th-century drawings and watercolours of animals collected by the founding father of zoology Conrad Gessner and his fellow Swiss successor Felix Platter. These and many more illustrations feature in her new book on early modern natural history illustration, Eye For Detail (Reaktion Books, 2017) and I invited Egmond (with the kind permission of Amsterdam University Library) to put together a gallery of some of these amazing illustrations.

Inspired, I flipped through an online copy of Historia Animalium (on the brilliant website archive.org). I was able to locate many of the reproductions of many of Egmond’s originals, but I love this engraving of a bear, with its beautifully rendered fur.