This
is the second post in my series on sleep and memory. Check out the first post in the series for an introduction to the four stages of sleep and early
research on the interaction of sleep and memory.
Rapid Eye Movement (REM) or
dreaming sleep is not exactly restful. Dreaming uses up energy, and our bodies
use more oxygen while in REM sleep than when we are awake! Since the purpose of
REM sleep can’t be to replenish energy, something else must be going on in the
brain. This “something else” is suspected to be the organization and
preservation of memories.
 |
| Image by blog author. |
During childhood, 50% of
the time spent asleep is devoted to REM sleep. Childhood is also a period of
intense learning. As kids, we learn how to walk, how to read, how to make
friends, and many other valuable skills we’ll rely on our entire lives. The high
amount of REM sleep in childhood is likely crucial for remembering what we
learn as kids
 |
| The author as a child trying to learn while sleeping. |
In contrast, REM sleep
deprivation makes learning difficult. REM sleep deprivation during childhood
development is especially detrimental and can cause problems with the visual
system and behavioral differences that remain in adulthood. [1]
REM sleep is also linked
to efficient learning since the more REM sleep a person gets after learning the
more productively they can learn. To foster effective learning, the length and
quality of REM sleep increases after learning in children and younger adults. [2]
Getting sufficient REM
sleep improves task performance and helps people retain memories in challenging
circumstances. Here’s an example: in a study by Jeffery Ellenbogen and his
colleagues, study subjects were asked to memorize two similar lists of words.
Subjects who got normal amounts of REM sleep didn’t confuse the two lists as
much as subjects who were deprived of REM sleep. [3]
The benefits of REM sleep
for retaining memories are less prevalent in older adults. The ability to learn
and remember things decreases with age as does the duration and quality of REM
sleep. Older adults do not show the same increase in REM sleep after learning
that younger adults and children do. This is likely linked to the fact that
older adults tend to be less efficient learners than younger people.
Most of the evidence of
the role of REM sleep in memory retention I’ve discussed comes from sleep
disruption studies. Where participants are first taught a new task, told a
story, or asked to memorize a list of words. After this, the study subjects’
brain waves are monitored during their sleep. The control group are allowed to
have a normal night’s sleep, while the experimental group are woken up as soon
as they enter REM sleep, thus depriving them of only REM sleep. Then, the next
day the subject’s memory of what they learned is tested to see how REM sleep affected their memory.
The results from these
studies seem conclusive—REM sleep is crucial for memory retention! But, there
is more than one type of memory. Remembering how to ride a bike requires
different brain activity than remembering what you ate for lunch on Tuesday.
Does REM sleep help us remember all types of memories or just a few types? Do
other sleep phases play a role in memory as well? Find out in my next post.
[1] Li, Ma,
Yang, and W. B. Gan. “REM sleep selectively prunes and maintains new synapses
in development and learning.” Nature Neuroscience, vol. 20, Jan. 2017, pp. 427-437. doi: 10.1038/nn.4479.
[2] Hornung, Regen, Danker-Hopfe, Schredi, and I. Heuser. “The Relationship Between REM Sleep and Memory Consolidation in Old Age and Effects of Cholinergic Medication.” Biological Psychiatry, vol. 61, no. 6, Mar. 2006, pp. 750-757. ScienceDirect, doi: doi.org.ezproxy.cul.columbia.edu/10.1016/j.biopsych.2006.08.034
[3] Ellenbogen,
Hulbert, Stickgold, Dinges, and S. Thompson-Schill. “Interfering with Theories
of Sleep and Memory: Sleep, Declarative Memory, and Associative Interference.” Current
Biology, vol. 16, no. 13, 11 July 2006, pp. 1290-1294. ScienceDirect,
doi : doi.org.ezproxy.cul.columbia.edu/10.1016/j.cub.2006.05.024
