Indifferent - Nightreports - Nightreport 1
This e-mail is coming directly from the sleeping lab
at Stanford. Supervisor is no
one else than Dr. Stephen LaBerge. I'm glad to make my first
Night-Report and take this occasion to explain some of those things,
which are going on when I spend my nights here in Stanford.
For what those measurements? These three measures are indicators for
different sleep stages. All in all there are five different
sleep-stages. All these stages differ in the curves from the EEG, EOG
and EMG. When we fall asleep we can observe sleep stage 1. The EEG
shows alpha-waves and the eyes start to roll slowly. Where exactly the
sleep-onset is, is hard to tell. Ten people would say something
totally different. Per definition the sleep-onset is when the person
who falls asleep actively suppresses the perception of the external world. An example should
clarify this point, if we take someone who is pretty tired and we would place
him in front of a big light and we would turn on the light every 15
sec for 2 sec. Than we would ask this person to push a button every
time when he sees the light. Per definition, this person would sleep
when he is no longer able to push the button, but the light is on.
Would we ask him afterwards if he saw the light, he would answer
"No, the light was off".
REM-sleep and dreaming
And now? After we went through all those stages we start to dream. Dreams are highly correlated with the REM-stage (Rapid Eye Movement), this means if we wake people up from a REM-stage, 80% of the people would probably remember a dream. What are the indicators for REM-stage?
That our body is paralyzed is good, because this prevents us that we do not act our dreams in the real world. After the REM-stage the whole cycle starts from the beginning up to six times per night. If we have a normal person in the lab his sleep profile would look like figure 3.
The electroencephalogram (EEG) is a time-varying electrical signal recorded from electrodes attached to the scalp of a human subject. The signal arises from action potentials - short-lasting changes in potential difference - within the neural cells of the brain and, as such, are a measure of brain activity. Identifiable features of the EEG can be used to differentiate between the brain states of the patient, for example, during sleep, quiet wakefulness, etc. Any recording system for the EEG requires the following components:
A number of different configurations have been proposed for electrode placement but the 10-20 International System is now the most common layout in use. The electrode positions and labels for the 10-20 system are shown in the figure 4.
Borbély, A. (1998). Das Geheimnis des Schlafs. Neue Wege und Erkenntnisse der Forschung [Electronic version]. (Original work published 1984. Stuttgart: DVA.). Retrieved May 23, 2001, from http://www.unizh.ch/phar/sleep/buch/TITEL.htm
Davila, C. E. (1997/Administrator). Normal EEG Rhythms. Retrieved October 25, 1999, from http://www.seas.smu.edu/~cd/EE5340/lect11/sld018.htm
Garskadon, M. A. (1980). A manual for polysomnography (PSG) technicians. Unpublished manual: Stanford University.
[13. Juli 2004] [kontakt]