Sleep cycles, circadian rythms, etc

[dst]

On all those studies which took people and placed them in caves/prolonged darkness, it's known the body goes into a 25 hour "day/night cycle". But is that cycle itself roughly synced with the actual day and night (even when the person can't tell whether it's day or night outside), and if so, how much is the error margin?

 

[Poop-Loops]

I'm pretty sure you can switch around the day/night sync if you alter your sleeping habits. I mean, when you go to a different time zone, your body operates on the old timezone for a while before you adjust. However, adjusting isn't an automatic thing. You need to get to bed and wake up at the correct times.

 

[dst]

Yeah, but what I'm looking for is whether humans (or any animal for that matter) can sense that it's daylight outside regardless of local conditions. I mean, if we took a person and locked them in a pitch black box with an electric light and air supply, would they still function as if you locked them in a pitch black box with a window (and the other things)?

 

[ghost02]

Probably. Same sleeping habits.

 

[glondor]

No one locked in a box would function in any manner that would appear normal. Light deprivation as well as never having darkness is used as a form of torture. I recall many pow's who were locked away in darkness for months lost all sense of time and reality. Those who were in cells that were lit 24/7 had no sense of time as well.These methods were used to break your will.

 

[Moonbear]

On all those studies which took people and placed them in caves/prolonged darkness, it's known the body goes into a 25 hour "day/night cycle". But is that cycle itself roughly synced with the actual day and night (even when the person can't tell whether it's day or night outside), and if so, how much is the error margin?

It's not necessarily 25 hours, but is greater than 24 hours. If you stop and think about that, you'll realize that within a few days, they would no longer be in phase with natural daylight hours, because their sleep/wake cycle will shift a half hour to an hour every day. This, by the way, is how a circadian rhythm is defined...it must free run in the absence of environmental time cues. If whatever behavior/function is being measured disappears in the absence of daylength cues, it is considered a diurnal pattern, not circadian.

The other term you are seeking (even if you didn't know it) is "entrainment." This is the synchronization of the onset of a particular behavior/function to the prevailing daylength or among other animals in a group.

 

[dst]

Yeah, I'm just looking for documented ways in which people could sense something in a very indirect manner. In the same way some people with arthritis can predict the weather, I would have thought everyone has some form of natural cue that acts completely behind the scenes or at least in a very obscure fashion.

As for people being locked in a box, it's a hypothetical situation, and the point isn't about people being sleep/light/item X deprived, nobody talks about the cat being deprived of air in Schrödinger's cat example ;)

And yes, it would be entrainment I'm looking for.

It's not necessarily 25 hours, but is greater than 24 hours. If you stop and think about that, you'll realize that within a few days, they would no longer be in phase with natural daylight hours, because their sleep/wake cycle will shift a half hour to an hour every day. This, by the way, is how a circadian rhythm is defined...it must free run in the absence of environmental time cues. If whatever behavior/function is being measured disappears in the absence of daylength cues, it is considered a diurnal pattern, not circadian.

Well, I guess when it comes to semantics it stops right there.

What's the next closest thing? Anything extraordinary or counter-intuitive in the same way that people with arthritis can tell when it will rain?

 

[Moonbear]

What's the next closest thing? Anything extraordinary or counter-intuitive in the same way that people with arthritis can tell when it will rain?

Can you clarify what you mean? Are you looking for sensory signals animals use other than light to entrain rhythms? Or do you mean less known ways that people can detect changes in the environment other than seeing rain or their head suddenly being wet?

If you mean the former, sure, in the absence of light cues, if other environmental cues are provided on a regular basis, animals can use some of those to entrain their rhythms...not as well as with daylight, and overridden with daylight, but nonetheless, other cues can be used. A good example would be rodents housed in constant darkness for experiments on cirdadian rhythms, but in which staff enter the room at the same time every day to feed them or clean cages. They can become synchronized to that feeding/cleaning schedule. Likewise, the activity in the building varies with time of day (everyone arriving at 8 AM starting to rattle carts around and make noise, phones start ringing, traffic outside the building increases with vibrations the animals can detect, and then all is very quiet during the night, etc.). People who study circadian rhythms have to be very aware of these other environmental cues that can entrain rhythms, and will do things like feed on irregular schedules (load up lots of extra food in cages so it's always there, regardless of the time someone comes into replenish the food and water), use white noise generators to prevent external sounds from being noticed, choose interior rooms of buildings so vibrations transmitted through walls from outside are not detected, etc.