Let's start with a story. See if it sounds familiar. But be forewarned: There's a surprise twist at the end.

It's about an entrepreneur. We'll call her Sally. Like many entrepreneurs, Sally sometimes gets overcommitted and overstretched. 

One week, for example, she has an important client presentation, plus a new product rollout, and a big deadline on a project that could really make the difference for her company. 

At the same time, she's balancing life: family, fitness, friends, health, and self-care.

Something has to give, and it's her sleep schedule that goes first. She stays up late, gets up early, burns the candle at both ends to get things done. 

Then the weekend comes, and she crashes: sleeps in, maybe gets to bed early. By Sunday evening, she feels rested, refreshed, and rejuvenated -- ready to tackle the new week.

Now for the surprise twist. 

It comes from an eye-opening new article in the journal Trends in Neurosciences, which synthesized decades of research on what happens to our brains when we accumulate a sleep debt, and then try to make up for it. 

In short, it's not what we think happens -- and not what we've been taught to think over the years. 

Instead, according to authors Zachary Zamore and Sigrid C. Veasey of the Chronobiology and Sleep Institute at the University of Pennsylvania, there are at least three crucial things to know:

  • First, when we accumulate a sleep debt, we lose some of the subjective ability to judge how that lack of sleep affects us. 
  • Second, even though we don't realize it, objective tests show that we continue to have "deficits ... in vigilance and episodic memory" even after "2-3 nights of recovery sleep." Key: The deficits persist even if we feel "less tired" after recovery sleep.
  • Finally, and perhaps most alarmingly, studies suggest that this persistent sleep loss -- even when we try to catch up on it -- can lead to "heightened susceptibility to neurodegenerative disorders, including Alzheimer's disease ... and Parkinson's disease (PD)."

This is a really interesting and alarming journal article, running nearly 10,000 words. Among other things, it brings home just how difficult and crucial it is to study what happens when people become sleep deprived:

  • Difficult, because of the ethical and practical considerations. (How can you measure sleep deprivation without causing it, and how can you cause it despite recognizing its significantly negative effects? As an account in The New York Times about the study pointed out, in some sleep-deprivation experiments on animals, the animals don't survive.)
  • Crucial, because as Zamore and Veasey concede, "sleep disruption is an inevitable occurrence in modern societies." (Simply knowing that sleep deprivation is bad for you doesn't change the fact that sometimes we run out of hours in the day, and have to make tough choices.)

For that matter, it would be no challenge to come up with many other studies describing additional negative effects of sleep deprivation. I've written about many of these:

Yet, as much as I hate to admit it, even though I'm the person who wrote all these articles, I'm also the person giving up sleep to write this article right now, because I couldn't find time to get everything done during the day.

Look, most of us know the things we have to do in order to become reasonably healthy and live long enough to accomplish the things we aspire to in life.

And, as I write in my free e-book Neuroscience: 13 Ways to Understand and Train Your Brain for Life, there's nothing more fascinating than the human brain, and the unexpected ways in which it works. Sleep is always at the top of the list.