A 2016 experiment by researchers at UC Irvine established a link
between autonomic nervous system activity during sleep and memory
consolidation. Participants in the study were given Remote
Associates Test (a creative word association test) which was
followed by the treatment: either a nap or quiet wake time.
Following the treatment, a second Remote Associates Test.
Individuals who napped showed improved performance on the second
test compared to those who did not. The researchers found that
heart rate variability and time spent in each sleep stage accounted
for 73% of the improvement observed.
Regarding the experiment, which of the following is essential
for consolidating the creative word test memories?