My own experience makes me think that most people can do it (although it is obvious that we all are different and some will need more sleep than others, of course). What makes me think that most people can do it is that right after I graduated, before I found a PhD grant, I went to work for a while for a company and suddenly, life became dull. Within a couple of months, I found myself set in an everyday routine, where I woke up at 7 to get to work at around 8.30, had lunch at around 12.30 with a coffee break at 10.30, then resumed work at around 1.30pm until 5 or 6 or even 6.30pm, by which time I was quite tired, and started to go back home using public transportation, arrived there between 7.00 and 8.00 pm, then had dinner, watched TV a bit, and was totally knackered at 11.00pm.
After several months of this routine, I remember it was absolutely impossible for me to stay awake after 11pm. There was nothing I could do to keep my eyes open and I was barely 25 or 26. I also remember clearly thinking that spending whole nights in front of my computer was something I was certainly too old to do again, like what I was doing when I was younger, (i.e. between 14 and 22). I really thought must suddently have gotten old and that sleepless nights were behind me.
Then, after about 2 years of a dull life when I literally dropped asleep at 11.00 pm to wake up at 7.00 am (therefore thinking that I absolutely needed 8 hours of sleep), I managed to get a PhD grant and life rapidly became interesting again, and now that after many years, I am in a position where I get to drive some wonderful projects, everyday life is so exciting that I do well with only 4 hours per night.
My analysis is that it is not sleeping techniques that got me there, but managing to find exciting things to do, and being solicited by many people who count on me to get somewhere. Whenever my daily level of excitement drops (in between deadlines, or during vacations), I return to sleeping 8 hours (or sometimes even more !).
I think that if I landed on a desert island without a pen and a piece of paper or a book and no way to do anything, I would get bored to death and would sleep 12 hours a day (provided I could find enough to eat in the 12 hours I was awake).
As for the tests, there are many statements in this forum that say that scientists who specialise on memory have no idea about what memory techniques can make you achieve. I think this is the same for sleep tests: if you perform tests on people who live a dull life, you will get results that show that their life quality will deteriorate if they are forced to sleep 4 hours only. Sleep deprivation on people taken at random in the street could be assimilated to torture. Now, on the contrary, perform those tests on people whose life is full of excitement and I’m ready to bet quite a lot that results will be different.
To end on this, there are periodically some TV broadcasts on Medical Practitioners at hospitals emergency departments. All these footages show that (in France at least) the standard day of an emergency MP will last for at least 24 hours of uninterrupted work (they periodically have coffee breaks) and sometimes, to replace colleagues on vacation, they can stay up and taking care of patients for as much as 48 hours in a row or even more…
And I don’t think they are selected on their ability to not sleep. I think that they are ordinary people who (by interest or by necessity) ended up working in an emergency department with such working hours, and that they can cope with this rhythm because on busy days, as soon as they have finished with someone bleeding to death after a car crash, they have to deal with a heart attack, then someone with food poisoning, or who just tried to commit suicide, then, … and this goes on for 24 or 48 hours…
Hundreds of such medics can do it, so I firmly believe that it is your lifestyle that determines how many hours you need to sleep (with occasional variations between people, of course, and a minimum number of hours below which you simply cannot go on for a long time, but in my experience, this is much much lower than what you would think).
In my case, I am fine with 4 hours of sleep per night for sustained (interesting and exciting) activity over several weeks/months, and for exceptional deadlines, I can go down to 1 or 2 hours per night, but this will strain me if I do this more than a few days. Sometimes, I will work all night through before a very important presentation (for a conference where I will talk in front of possibly several hundred people). I find that not sleeping will slow me down and allow me to do a better presentation, because I will be more focussed on what I say and because I am slower, I talk more clearly for the audience. When this happens, I nevertheless try to sleep at least 30 minutes or 45 minutes, and so that I have psychologically slept for one night, I go through a complete routine, with brushing teeth, getting undressed, sleeping in a bed in a dark bedroom, then waking up 30 or 45 minutes later as if I had slept a whole night. Finally, I find that even a short shower will wash tiredness off me. If I have 1 hour left, I will rather go through a full routine including a 10-15mn shower (= ~35mn sleep) rather than lying unconfortably on a sofa for 1 hour. After a 1 hour complete routine with 10-15mn shower, I will be fresh again and ready for a new day, and I can do this for up to 3 or 4 days, but after this, I will need maybe 8 hours sleep to recover, or a couple of days at 5 or 6 hours sleep.
Btw, remember that tiredness is not cumulative: if you only sleep for 2 hours for 4 days and you believe you need 8 hours per night, don’t think you will need to sleep an extra 24 hours because you missed this amount of sleep. Your sleep deficit will cancel in one good night’s sleep (whatever it means for you).
In my experience, you should be able to easily go down to 6 (or even 4 hours), provided you can make your life more exciting… To me, 8 hours is what you need if you are in a life routine that may be full, but dull.
Try getting involved in more social activities where people depend on you (becoming president of a couple of societies, get invited here or there to make speeches on memory or music, or…) In my experience, you will see that you can cram into your life many more things than you thought you could).
P.
Finally, seeing that we did it, they painstakingly followed and we all went for a beer in a nearby café, and had a great time there. We came back to the hotel at 2.00 am and Paul and I went on working together on a project for a couple of hours.