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One Eye Open

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It's a dangerous world out there, with predators always lurking. So what on earth would give every single animal in the kingdom the gumption to think it could lay itself down each day, let down its defenses, and go to sleep? Well, turns out that many species might not be as "out cold" as land mammals. We join Charles Amlaner and Steven Lima and their team at Indiana University who show us iguanas sleeping only half their brain at a time. That’s right. They sleep with one eye open. (Cue the Metallica). That way, the iguana can watch for predators, as the other half of its brain takes a rest.

While these creatures stay half awake to protect themselves, for humans, the dangers of sleep can come from within. We visit the Hennepin County Sleep Lab, where Dr. Carlos Schenck shows us some of the most terrifying sleep disorders around.


Charles Amlaner, Steven Lima and Dr. Carlos Schenck

Comments [26]

Pete from Washington, DC

In the program, you discussed that marine mammals (including dolphins) are able to stay "half awake" during sleep whereas terrestrial mammals cannot do so. However, I don't believe that you mentioned that modern-day cetaceans evolved from a land-dwelling ancestor. Did I get that right? If so, then here's my question: did today's dolphins and their kin develop this ability independently over evolutionary time (an ability that their ancestors' never had)? Or did those particular terrestrial ancestors possess the "half awake" trait that other land-dwelling mammals lacked? Apologies in advance for geeking out but I'm really curious about this.

Jun. 07 2015 01:32 PM
Brian from D.C.

Another great show, but I got the point with the screaming 5 year-old, during the first segment, after the first 3 seconds. Just saying.

Jun. 07 2015 12:19 PM
LJ from Florida

Universities have been doing the same horrible experiments (including sleep experiments) on cats and other animals since before I was in college in the 80's earning a psychology degree. They drill into the sculls of the animals and put large metal devises permanently on top of their heads with electrodes. They "sacrifice" (kill) the animals during the experiment period. They often report that the animals seem depressed after the metal box devise is drilled into the animals' heads. What a surprise! They do the same experiment over and over, year after year, and often on the government's dime. I found out by reading industry publications that this is because many university and other scientists make a very good living at the expense of millions of animals and taxpayer funds. The universities and companies make a lot of money doing these experiments. They will never say that understand sleep, because then they can no longer make money. Same with cancer. This show failed to ask deep questions and instead seems to take whatever they are told as fact. Not good journalism, in my opinion.

Jun. 07 2015 11:43 AM
Kam from Los Angeles

I just heard this episode for the first time and found the small bit about night terrors quite interesting as I am a person who gets them, and just actually went through one last night.

They are something that seems to occur about once a week for me, but only in the last few years...

Back in 2012 I was assaulted in Brooklyn walking home to my house. My assailant kept saying "Don't scream, don't scream" and I did not, I was terrified. The man punched me several times and took my bag.

After the incident, a friend said "You are supposed to scream no matter what"

Now in these night terrors I get, they come from fear of being attacked... not always by human, once it was fear of being attacked by a bird, once by a motorist... In the dream I know vividly that at the moments leading up to attack I am afraid of NOT screaming and I build energy and then suddenly i SCREAM. Loudly in the middle of the night, it wakes me up as well as my husband.

But then once I awaken, and realize that I am in my bed, and safe... I can go back to sleeping soundly the remainder of the night

Dec. 11 2014 05:55 PM
art davis from Overland Park, Kansas

Humans did not lose the ability to sleep with one eye open.

In college I had a German professor. He was with the German Army fighting on the Eastern Front. Toward the end of the war, when Germany was losing, his unit was in a daily retreat. During the day the soldiers would fight, at night, the German soldiers walked in line with a hand on the shoulder of the soldier in front until morning.

Survival and fear trump sleep.

Dec. 08 2014 11:36 AM
Adrienne from KCMO

As a previous commenter mentioned back in 2007, is there a way you could put some sort of warning before the rather graphic description of cat experiments/vivisection? I know you have done this in other shows with sensitive material and although the part in question is brief - from about 5:00-7:00 on the audio file, for those who wish to skip over it - I believe that a warning might be warranted in this case. Otherwise, an entertaining show as always.

Jun. 29 2013 06:44 AM
ColoradoDoug from Colorado

Sleeping with your eyes open. We have rescued several deaf dogs over the years and too the one, all have spent the first few months sleeping with their eyes open. How do we know their asleep? They snore. Some make a purring noise, others, like the Boxers, snore louder than I do, so says my wife. Some of the dogs will awaken very quickly when their eyes caught movement. Others, the Boxers, snore through just about anything. To wake the deaf dogs, we softly stroke them just behind the ears. Most wake up immediately, others (read Boxers here) just get a goofy grin on their faces and continue to sleep.

Mar. 17 2013 01:38 PM

I've always been a very light sleeper and always wake thinking I heard something or that the door is opening. Very paranoid sleeping habits and I never really understood why. I still sleep with a fan so that it drones out some of the background noises that would always wake me. I guess it's still ingrained in my dna to be on the look out, even in sleep mode. Cool story!

Jan. 29 2013 03:13 PM

Hey. I just wanted to comment on Hannah's situation. I am now 24, but until I was 3 yrs old I never slept for more than 30 minutes at a time. It turned out later that I was really allergic to grains and milk and the allergy caused it somehow. My mom would never had guessed as I didn't have any other symptoms. So that's worth checking.

Apr. 16 2010 08:22 PM

My answer is rerponse to the comment number #6 in which a very genuine question was put up by the little boy and The answers is that "Fishes Do sleep" as it is being widely claimed by the scintists all over the world and by default we are being taught this fact.

Dec. 05 2009 06:07 PM
Victoria from WI

I listened to this episode on a long bike ride on a brisk day, so I was full of energy and wide awake by the end of the program. How come I yawned with the woman reading the credits? Are yawns really contagious, even via podcast?

Nov. 13 2009 11:32 AM
Susan from Little Rock, AR

I really enjoy your programs, both technically and topically. In this program there was a brief mention of night terrors, and I started thinking about nightmares. Since we need a "good night's sleep" so badly, why do our brains concoct stories that are so disturbing that they can wake us up and make it difficult to get back to sleep?

Jul. 06 2009 01:07 PM
Stacey from Sarasota, FL

What is the name of the song you play approximately 40 minutes into the mp3?
Who is the artist?
It's awesome!
Thanks :) Great show, by the way!

Jun. 08 2009 01:31 PM
Peter from CT

Your program was very enjoyable. Since listening to it, I've read several times that bullfrogs do not sleep. So, what gives? Are they the only animals in the entire world (along with fish possibly, according to the post above) that don't sleep? Are they unique among frogs - or do no frog species sleep?

Looking forward to - and waiting patiently for - season 6!

May. 12 2009 11:29 PM
shannon lundberg from portland oregon

talk of predation risk makes me think of sleeping in the mountains. It's common to wake up multiple times throughout the night. My dreams are intensely vivid, some sticking with me for decades, and I wake up feeling well rested.

Apr. 25 2009 05:21 PM
Bruce from New Hampshire

This show was painful to listen to. The extraneous noise and chatter was just over the top. While I enjoyed learning the facts as they appeared during the occasional lulls, I was definitely of mixed emotions as my car found its way out of the listening area of the local Public Radio station.

Mar. 13 2009 04:39 PM
Darren from Washington DC

who was the electronic music by? on the one eye open episode.

Mar. 26 2008 03:24 PM
Joe from San Diego, CA

Outstanding program. I learn more on RadioLab then in school. Please keep up the good work. Joe

Aug. 31 2007 04:03 AM
PJ Maccias from Austin, TX

Your program on sleep was so devoted to mediocre revelations that you skipped over some facts I consider imperative, especially since you say your program investigates. I was floored when you mention so casually that "Dr. Whoever looked into the brains of cats and guess what he discovered?"Wow! now we know this and this about cat sleep.
How do you think he got into the brains of cats? Where do you think he got the cats? Do you think they volunteered?
All of you seemed so joyful that discoveries were made from more cruel animals experiments. But you didn't go there. You were focused on outcome. If you ever see a photo of a cat with this equipment put INTO his skull, you wull never forget it.
Are we all smarter now from your program? Did a researcher get big bucks for these enlightening tidbits? Didn't you just do a program on morality?
Your 'Radio lab' is on par with People Magazine.Terry Gross come back please!

Aug. 16 2007 12:51 AM
Radio Lab

Hi Andrea, your son asks a very very good question. The short answer is: we have no idea! Fish don't have eyelids, so IF they sleep, they don't close their eyes when they do. So scientists have tried to monitor fish brain activity. But they've had to take the fish out of the water to do that, which makes the measuring kind of meaningless (because if you were a fish out of water, would YOU sleep?). so as far as we know, your son's question remains very much answered.

Jul. 29 2007 08:11 PM
Andrea M.

The day before I heard this episode (thanks to the suggestion on This American Life) my 11-year old son asked me if fish sleep. I thought I might find the answer during the show. But, fish were never mentioned even though every other category of creature was mentioned. So, do fish sleep?

Jul. 19 2007 12:12 AM
Radio Lab

Hi David,

You can contact us by sending an e-mail to

Radio Lab

Jun. 28 2007 11:29 AM
david hamlin from home

not sure if this is the right forum, but can you tell me how to get in touch with the writer(s)/producer(s) of this episode.

It was excellent and I have an idea to share - not just fawning praise, but I'll do that too if necessary


Jun. 26 2007 10:27 PM
Dixie Yid from East Coast

I really enjoyed this program and it really got me thinking about the meaning, mechanics and purpose of sleep. You can find my reflections on this episode of Radio Lab here:

-Dixie Yid

Jun. 13 2007 08:01 AM
V. Philbrick from Saratoga, California

We have a house without air conditioning. However, we have a 'whole house' fan plus we circulate the house air with a very well filtered furnace system. Our community air quality is good & we don't live on a street, but have a long driveway. My wife tells me that fresh air sucked in by the whole house fan is bad for her plus the filtered circulating air also makes things worse. I tell her that it is not the air, but some other problem which causes a problem for her. Is moving air "bad" for you when you sleep? Is outside air "bad" for you when you sleep? Thanks. V. Philbrick

Jun. 05 2007 02:04 AM
Emmet from Creswell,Oregon

Thanks for the program I heard on OPB. It was beyond interesting. Great job. Would like to learn more,......but I am going to sleep now!

May. 26 2007 01:22 AM

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