Echidna: Dreamers?

Summary: Do echidnas dream? Join Kiersten as she travels into the sleep cycles of the echidna to find out if they dream.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean

 

Show Notes: 

“Monotremes and the evolution of rapid eye movement of sleep,” J. M. Siegel, P. R. Manger, R. Nienhuis, H. M. Fahringer, and J. D. Pettigrew. Phil. Trans. R. Soc. London, B (1998) 353, 1147-1157. 

“The Echidna Tachyglossus aculeates Combines REM and Non-REM Aspects in a Single Sleep State: Implications for the Evolution of Sleep,” by J. M. Siegel, P. R. Manger, R. Nienhuis, H. M. Fahringer, and J. D. Pettigrew. The Journal of Neuroscience, May 15, 1996, 16 (10): 3500-3506.

 Music written and performed by Katherine Camp

 

Transcript 

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

This episode continues echidnas and the eighth thing I like about this rule breaking mammal is the possibility that they may dream. I’m not kidding listeners, echidnas may actually dream. Let’s dive into this subject by finding out what happens when echidnas sleep.

Discovering what happens when echidnas sleep has been a long a winding path. First, it’s pretty difficult to determine what a hard to find, nocturnal animal is doing when they’re sleeping. So most of the research done involving echidna sleep is done with the short-beaked echidna, Tachyglossus aculeates, because they are more easily found. 

In 1972, a report was published about the electrophysiological study of the short-beaked echidna. They were interested in the waking and sleeping state of the echidna. The way you study that is by recording the electrical impulses created by the brain during different activities. The 1972 study showed that echidnas do not enter REM sleep, the state of sleep in which dreams occur. Echidnas remained in a non-REM sleep the entire time they were unconscious.  

Based on this information, researchers postulated new hypotheses on when sleep developed two sleep stages. Since echidnas are biologically some of the oldest living mammals, some say primitive but I think that word makes them sound unimportant, the stages of sleep they exhibit could have meaningful implications on when mammalian sleep developed two distinct sleep stages.

For years science excepted this result for the 1972 study. There was no reason to question the results. The research was sound and a second study published in 1996 seemed to support these results. The second study actually found that the typical sleep patterns of non-monotreme mammals, which is every mammal except echidnas and platypus, did not match the sleep patterns of the echidna. 

The really interesting result of this study was that they found that echidna sleep resembled both non-REM sleep patterns and REM sleep patterns in the same cycle. This is significant because in the average mammal REM and non-REM sleep happens in separate cycles. Using different methods of judging sleep  and waking activity in the brain, revealed a truth that called for a reevaluation  of the previous results.

Really fascinating! Who knew the sleep patterns of an ancient-lineage mammal could mean so much to modern research? 

With these two studies kind of rubbing against each other, further research was definitely needed. In 1998, a study did look closer at the sleep patterns of the echidna. The previous two studies had used changes in EEG, electromyogram, and eye movement to determine whether the echidna actually experienced REM sleep. These researchers recognized the discrepancies created using these recoding methods and decided to look at the neuronal activity in the brainstem. 

The 1998 study added another layer to the echidna sleep mystery. Using new evaluation methods this study showed that echidnas do experience a sleep state resembling REM sleep in the brainstem, while the forebrain remains in a state resembling non-REM sleep.

One of the questions that arose during this line of study was why do echidnas not show typical signs of REM sleep such as the rapid eye movement that gives this sleep cycle its name. Twitching of various body parts, as well as, eye movement is indicative of REM sleep in many mammalian species, including platypus which is the other extant monotremes on the planet. So why don’t echidnas display twitching muscles during REM?

The scientists in this study thought that might be due to the fact that echidnas sleep in more exposed areas than platypus. The twitching of their spines would be audible and visible to predators, but in the last episode I just talked about how echidnas dig dens into the side of sloped ground. So, I don’t know if I buy that explanation. They may need to go back to the drawing board on that. But this evidence gives them one more hypothesis on when REM sleep developed in mammals. The forebrain aspects of REM sleep may be recent inventions in the mammalian line.

How does any of this relate back to the title of this episode? REM sleep is the sleep cycle when dreaming happens. Research into human sleep patterns shows that dreaming happens during the REM sleep cycle. Mammals that experience REM sleep may also dream. Now the cortex of the brain must be activated during REM sleep to produce dreams, and what we just learned about echidna sleep tells us that their brainstem is involved in their REM sleep. 

So do echidnas dream? They do have a large neocortex compared to other mammalian brains, and I’ve just shown that different routes of research can shed more light on what is actually happening in an animal. Maybe brainstem REM sleep also creates dreams and we just haven’t found evidence of it yet. It’s an intriguing question and I’ll leave you with one more before I end this episode. If echidnas dream, what do they dream about?

Thanks again listeners for following me down the winding path of the echidna. I’m glad you joined me today because my eight favorite thing about them is the possibility that they dream.

 

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

Join me next week for another episode about echidnas.    

 

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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.