As an airline employee who sometimes faces large shifts in sleep times, I've become quite worried about brain health. Papers like this and Matthew Walker's recent popularity seem to have brought more attention to the issue. Last week I slept from 9pm - 2:30am, 12am - 7am, 7am - 11am, 9pm - 6am, in that order. The week before I had to wake up at 1am two days in a row. It isn't possible to function normally on such a schedule and it's horrible for your health, yet that fact is completely ignored. I'd be considered alarmist and met with a "suck it up" attitude if I were to take a stand against such things. The FAA wipes their hands of it by saying that it's "your responsibility" to make sure you've gotten adequate rest and to call in fatigued if you haven't, but one would soon lose their job for doing so as often as would truly be required. Flying an airliner is easy, but we have two pilots because one or both are often totally exhausted, whether they realize it or not. Operating on "stem power" is a phrase sometimes used, as in, 'so tired that your higher level functions are shot and you're operating on brain stem power alone'.