I noticed your question the first time around and hoped that someone with
more expertise than I have would answer it. Repetition drove me to trying
to figure out the answer for myself. I'm not sure that I'm right about this
so please forgive me if I err. So far as I can tell, there is little doubt
that light is probably the most important synchronizer of the circadian
rhythm. In the absence of light, changes in temperature and meals may also
suffice to regulate the cycle.
So long as there are REGULAR CHANGES in such things as temperature or light
or REGULAR CUES (such as meals), one cannot tell if the 24 hour cycle is a
response to environmental cues or if there is a built in biological clock.
To determine if there is a built in biological clock, one has to remove the
REGULARITIES in the environment. Accordingly, one might provide either
continous bright light, dim light or no light. The key, I think, is to have
a constant, unchanging level of illumination so that there are no cues to
the passage of time and so that light changes will not trigger any
physiological "biological clock" processes. Since circadian rhythm may also
be regulated by changes in temperature or the presentation of meals or
anything else that signals the passage of time, the environment has to be
controlled to be devoid of these cues as well. I tried checking Psych
Abstracts and, so far as I can tell, some researchers have tested humans in
underground caves in conditions stripped of time cues with subjects left to
control for themselves whether the light was on or off, when they ate and
what they got (bacon and eggs could provide a hint), and what they did
(activity vs sleep). In other experiments, the light was kept at a
continous level.
I have found this an interesting exercise in that some of what I read
suggests that circadian rhythms for sleep can become dissociated from
circadian rhythms for temperature. Also, one abstract reported considerable
individual variations in sleep-wake cycles among subjects deprived of
temporal cues for a month: wake cycles ranged from 10 to 30 hours. In this
study, subjects were asked to press a button every time they thought an hour
had passed. Increases in duration of wake cycle were associated with
increases in the amount of time experienced as an hour.
Hope this helps.
Val
Dr. Valerye McDonald
Professor
Psychology Department
University College of the Fraser Valley
Abbotsford, B. C.,
Canada
-----Original Message-----
From: JL Edwards <[EMAIL PROTECTED]>
To: TIPS <[EMAIL PROTECTED]>
Date: June 28, 1999 8:18 PM
Subject: Sleep question
>Hi ...
>
>I think my question may have been lost in the shuffle. I hope somone can
>help me for I'm still struggling with the research regarding the circadian
>rhythm of sleep. As I mentioned in my initial email, current researchers
>have criticized previous research indicating that the sleep CR is 25 hours
>long, basing this criticism on the fact that bright levels of light were
>used. In fact they conclude, "Light is the most powerful synchronizer of
the
>biological clock." The current researchers, who are reporting a 24 rather
25
>hour cycle, also used light, constantly exposing their subjects to
"subdued"
>levels. I don't understand how they can obtain a valid measure of the
length
>of CR when they also used light. Wouldn't it be better to put subjects in a
>naturalistic setting where they would be exposed to natural light and dark
>and have them record physiological functions, time at going to
>sleep/awakening, etc.?
>
>Thanks in advance to anyone who can help me!
>
>JL Edwards
>[EMAIL PROTECTED]
>
