Why We Sleep

participants fall back asleep.
The subjects had the task described to them before going to bed in the sleep
laboratory with electrodes placed on the head and face so that I could measure
their sleep unfolding in real time on a monitor next door. The participants also
performed a number of trials before getting into bed, allowing them to get familiar
with the task and how it worked. After falling asleep, I then woke subjects up four
times  throughout  the  night,  twice  from  NREM  sleep  early  and  late  in  the  night,
and twice from REM sleep, also early and late in the night.
Upon  awakenings  from  NREM  sleep,  participants  did  not  appear  to  be
especially creative, solving few of the anagram puzzles. But it was a different story
when  I  woke  them  up  out  of  REM  sleep,  from  the  dreaming  phase.  Overall,
problem-solving abilities rocketed up, with participants solving 15 to 35 percent
more  puzzles  when  emerging  from  REM  sleep  compared  with  awakenings  from
NREM sleep or during daytime waking performance!
Moreover, the way in which the participants were solving the problems after
exiting  REM  sleep  was  different  from  how  they  solved  the  problems  both  when
emerging from NREM sleep and while awake during the day. The solutions simply
“popped out” following awakenings from REM sleep, one subject told me, though
at the time, they did not know they had been in REM sleep just prior. Solutions
seemed  more  effortless  when  the  brain  was  being  bathed  by  the  afterglow  of
dream  sleep.  Based  on  response  times,  solutions  arrived  more  instantaneously
following an REM sleep awakening, relative to the slower, deliberative solutions
that came when that same individual was exiting NREM sleep or when they were
awake during the day. The lingering vapors of REM sleep were providing a more
fluid, divergent, “open-minded” state of information processing.

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Using the same type of experimental awakening method, Stickgold performed
another  clever  test  that  reaffirmed  how  radically  different  the  REM-sleep
dreaming  brain  operates  when  it  comes  to  creative  memory  processing.  He
examined  the  way  in  which  our  stores  of  related  concepts,  also  known  as
semantic  knowledge,  function  at  night.  It’s  this  semantic  knowledge  like  a
pyramidal family tree of relatedness that fans out from top to bottom in order of
relatedness strength.
Figure 14
is an example of one such associative web plucked
from my own mind regarding UC Berkeley, where I am a professor: