Highlights

A key function of deep NREM sleep, which predominates early in the night, is to do the work of weeding out and removing unnecessary neural connections. In contrast, the dreaming stage of REM sleep, which prevails later in the night, plays a role in strengthening those connections.

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When it comes to information processing, think of the wake state principally as reception (experiencing and constantly learning the world around you), NREM sleep as reflection (storing and strengthening those raw ingredients of new facts and skills), and REM sleep as integration (interconnecting these raw ingredients with each other, with all past experiences, and, in doing so, building an ever more accurate model of how the world works, including innovative insights and problem-solving abilities).

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What may at first blush have seemed like a modest asset awarded by REM sleep to a single individual is, I believe, one of the most valuable commodities ensuring the survival and dominance of our species as a collective.

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[T]he superior emotional brain gifts that REM sleep affords should be considered more influential in defining our hominid success than the second benefit, of inspiring creativity. Creativity is an evolutionarily powerful tool, yes. But it is largely limited to an individual. Unless creative, ingenious solutions can be shared between individuals through the emotionally rich, pro-social bonds and cooperative relationships that REM sleep fosters — then creativity is far more likely to remain fixed within an individual, rather than spread to the masses.

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[T]he proportion of REM sleep decreases in early childhood, while the proportion of NREM sleep actually increases, even though total sleep time decreases.

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Slowness was not the most sensitive signature of sleepiness, entirely missed responses were.

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Pilots suffered fewer microsleeps at the end stages of the flight if the naps were taken early that prior evening, versus if the same nap periods were taken in the middle of the night or later that next morening, when the attack of sleep deprivation was already well under way.

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[W]ithout sleep, our brain reverts to a primitive pattern of uncontrolled reactivity. We produce unmetered, inappropriate emotional reactions, and are unable to place events into a broader or considered context.

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If there is a red-thread narrative that runs from our waking lives into our dreaming lives, it is that of emotional concerns.

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When awake, we see only a narrow set of all possible memory interrelationships. The opposite is true, however, when we enter the dream state and start looking through the other (correct) end of the memory-surveying telescope. Using that wide-angle dream lens, we can apprehend the full constellation of stored information and their diverse combinatorial possibilities, all in creative servitude.

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It is sleep that builds connections between distantly related informational elements that are not obvious in the light of the waking day.

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Like an insightful interviewer, dreaming takes the approach of interrogating our recent autobiographical experience and skillfully positioning it within the context of past experiences and accomplishments, building a rich tapestry of meaning. "How can I understand and connect that which I have recently learned with what I already know, and in doing so, discover insightful new links and revelations?" Moreover, "What have I done in the past that might be useful in potentially solving this newly experienced problem in the future?"

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We cannot accumulate a debt without penalty, nor can we repay that sleep debt at a later time.

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One practice known to convert a healthy new habit into a permanent way of life is exposure to your own data.