Vor genau 10 Jahren war ich für ein Praktikum an der Stanford University bei Stephen LaBerge. Während der vier Monate verbrachte ich einige Nächte im Schlaflabor. Um mir die Zeit zu vertreiben, habe ich ab und an einen NightReport verfasst und an alle geschickt, die in meinem E-Mail-Verteiler waren. Nun will ich das 10-jährige Jubiläum nutzen, um die alten Reports in meinem Blog erneut zu veröffentlichen. Hier nun also der erste NightReport:
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.
Basically there is a team from about six people around the Lucidity Institute (The Lucidity Institute is Stephen LaBerges company where you can buy devices to induce lucid dreams). There are Stephen, Keith, Nathen, Mark, Frank and myself. But during the night recordings there are only three to four people. One is the dreamer, up to now Nathen was the one and only - and he is pretty successful in having lucid dreams. Than, there is Mark, he is the right hand from Stephen and he introduced me to the most things here in Stanford. Mark also showed me the application technique for EEG, EMG and EOG electrodes at the subject. Finally Stephen, he is the supervisor, double-checks everything and tries to answer all our questions.
After everybody is here, lets’ say around 7:00pm, we start with the application of the electrodes. This procedure takes about 2 hours (but we’re getting better!). There are 38 electrodes to stick on the head of the subject. After we fixed them properly we have to do several checks if everything is okay. Last time we had problems with the electrodes and it took us about 3 hours to fix these mistakes. After everything is done we send our subject to bed and we go to the next room with the computer. Nathen, the subject, lies in an about 2 to 2 to 1 meter big black soundproofed box - the booth. We have speak-contact and we also can watch him per video. Finally, we see his recordings on the screen and that’s the most exciting part. Before we allow him to sleep, there are some more tests for calibration. There is also a special task that Nathen has to do with his eyes. It is a combination of eye-movements. These eye-movements are the same task, which he tries to do later in his dreams.
Anyway, now it’s time to sleep and we can watch all of this on the monitor. What do we see on the screen? We see 32 lines, each line represent one electrode on Nathens head. There is the Electroencephalogram (EEG), which shows us electrical potentials from the brain, the Electrooculogram (EOG), which shows us electrical potential from the eyes (refers to eyemovement) and finally the electromyograph (EMG), which shows us electrical potential from the muscles at the chin.
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”.
The next stage is sleep-stage 2, which is a transition stage to the slow-wave sleep, or deep sleep. Some researcher refer this stage as sleep onset. The EEG shows now low frequented waves with low amplitude and from time to time we can observe K-complexes and sleep spindles. A K-complex is a single high amplitude (spike) and spindles are high-frequented waves with low amplitude. The sleep is getting deeper and we reach sleep-stage 3 and 4. Stage 3 and 4 are the same, differ only in the percentage of overall delta waves. Delta waves are low frequented waves with high amplitude. Now we are in the deep sleep.
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?
- The EEG resembles the brainwaves from wakefulness
- We can see bursts of rapid eye movements
- The body is paralyzed (observable in the EMG measure).
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 ups and downs during the night.
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:
- Electrodes attached to the scalp of the subject.
- Amplifiers to boost the electrical signals from the scalp. The amplitude of the input signals from the electrodes is usually in the range 10-100mV and high input impedance differential amplifiers are used to boost this level.
- Filters to filter the EEG signal before recording. High-pass, low-pass and notch filters are all used in this context. DC recordings refer to recordings without filtering.
- Recording unit which is used to keep a permanent record of the EEG signal. Originally the EEG was recorded on paper but digital recording is becoming more usual.
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.
Weitere Bilder von meinem Aufenthalt in Stanford finden sich auf meiner alten Homepage!
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