Tuesday, August 19, 2008

Nap Time

Have you ever wished that you could simply place a textbook under your pillow, and have all the information you need just seep into your brain while you sleep? My college roommate swore that it worked. And I mocked her for it. But as it turns out, there was some truth to her madness.

Though there is still some debate about which phase of sleep is most important for learning which types of skills, most of the recent journal articles** on the role of sleep in learning agree on one thing: The transfer of new information and skills, from working memory into long-term memory, happens while we sleep. Not only that, but the time spent sleeping allows your brain to optimize how and where you store that new knowledge in your brain, and can actually improve your skill level while you sleep!


Even a nap -- after a successful study session -- will help you retain knowledge and skills mastered during your study time and practice, but a solid 8 hours will help much more, since it is only in the deep, NREM and REM sleep cycles (which mostly happen during the second half of an 8-hour sleep) that you gain the effortless improvement of skills that my old roommate bragged about.

So, more sleep, less cramming, and better test scores...

What are you waiting for?

written by Larisa Naples, M.S.Ed., Ph.D.

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* Photos in this post are protected by a creative commons attribution license:
"TeddyBearNapping" is by Larisa Naples
** For those interested in the research behind this post, check out:
Walker, Matthew P. (2005) "A refined model of sleep and the time course of memory formation," in Behavioral and Brain Sciences, v. 28, pp. 51-104


NJTOM said...

"Even a nap -- after a successful study session -- will help you retain knowledge and skills mastered during your study time and practice, but a solid 8 hours will help much more, since it is only in the deep, NREM and REM sleep cycles (which mostly happen during the second half of an 8-hour sleep) that you gain the effortless improvement of skills that my old roommate bragged about."

If this is correct than how can the current medical advice to prevent Slow-wave sleep (Stage 3 and Stage 4 NREM) in infants be safe? Slow wave sleep (SWS) is when infants die of SIDS. So, doctors no longer allow infants to get SWS. Is this safe?

Larisa Naples, M.S.Ed., Ph.D. said...

Thanks for your comment and question, NJTOM.

All the studies I have read re: sleep and learning were conducted with test subjects that were either in high school or college, or were older adults. I have not seen any studies in this area focusing on infants (probably b/c it's harder to get them to reliably cooperate in the learning activities used in the experiments :-) ), so I'm afraid I cannot speak to the relationship between slow wave sleep and SIDS. What is the source of the medical advice you mention? Have you seen/read any good papers on this you could recommend? I'd love to take a look!

Peter White said...

I am not familiar with the science of SIDS, but this sounds like an orthogonal issue. Logically speaking, long periods of sleep can be both good for learning as well as be an aggravating factor for at risk infants.

NJTOM said...

I apologize in adavance. This is way too much info. But, this is the SIDS "Back to Sleep" Campaign in a nutshell if youu're interested:

Prior to 1992 over 90% of Infants slept on their stomachs or sides in the U.S. Now, over 76% infants sleep on their backs as this is believed to prevent SIDS and that's what the American Academy of Pediatrics recommends for the first year of a childs life. SIDS proper really means infants who die during Slow Wave Sleep (NREM Stage 3 and 4) due to a genetic defect probably about 1 in every 1000 kids have that make them susceptible to this. Putting an infant to sleep on their back severely diminishes Slow Wave Sleep (SWS) according to EEG's. Assuming the statistitics are correct(which Bowman and Hargrove of Scripps News service dispute) that SIDS rates have gone down this does not necessarily mean the practice is safe. SIDS rates are highest for infants between the ages of 2 and 5 months. SWS is first detected on EEG's at 2 months and 5 months is the typical age a child can lift their head from suffocating. Anyways, temporary memories humans make during the day are generally believed to be stored in the Hippocampus and then during SWS transferred for permanent storage in the neocortex. Notwithstanding the presumed positive impact of lowering SIDS rates I was just wondering if stopping the SWS process during the first year of life sounded like a good idea?

My favorite information on this is actually from letters to the editors of the Journal of Pediatrics. The best one is written by a sleep researcher named Rafael Pelayo of Stanford who is also questionning the safety of the SIDS Back to Sleep campaign just like I am. BTW, both infant pacifiers and putting an infant asleep on it's back do the same thing: inhibit slow wave sleep. Here's the Pelayo letter:

Bed Sharing With Unimpaired Parents Is Not an Important Risk for Sudden
Infant Death Syndrome: To the Editor
DOI: 10.1542/peds.2005-2748
Pediatrics 2006;117;993-994
Rafael Pelayo, Judith Owens, Jodi Mindell and Stephen Sheldon
Infant Death Syndrome: To the Editor

"However, from the perspective of the field of pediatric
sleep medicine, the policy statement’s laudable but narrow
focus on SIDS prevention raises a number of important
issues that need to be addressed. In particular, the
revised recommendations regarding cosleeping and pacifier
use have the potential to lead to unintended consequences
on both the sleep and the health of the infant.
The potential implications of a SIDS risk-reduction strategy
that is based on a combination of maintaining a low
arousal threshold and reducing quiet (equivalent to  or
slow-wave sleep) in infants must be considered. Because
slow-wave sleep is considered the most restorative form
of sleep and is believed to have a significant role in
neurocognitive processes and learning, as well as in
growth, what might be the neurodevelopmental consequences
of chronically reducing deep sleep in the first
critical 12 months of life?"



The Reply letter:
Pediatrics 2006;117;994-996
John Kattwinkel, Fern R. Hauck, Rachel Y. Moon, Michael Malloy and Marian Wallinger
Bed Sharing With Unimpaired Parents Is Not an Important Risk for Sudden Infant Death Syndrome: In Reply

Quote from the Reply letter:

The most current information regarding the etiology of
SIDS indicates that, at least for some of these deaths,
there is a developmental abnormality in the serotonergic
network in the brainstem, which results in the failure to
arouse or respond to life-threatening stressors such as
asphyxia and hypercapnia when asleep.9,10 Furthermore,
physiologic studies demonstrate that infants who sleep
supine have decreased sleep duration, decreased non-
REM sleep, and increased arousals11; this effect peaks at
2 to 3 months of age and is not evident at 5 to 6 months
of age,12 thus coinciding with the peak incidence for
SIDS at 2 to 4 months of age. The SIDS risk-reduction
strategy of supine sleep will result in a lower arousal
threshold and a reduction in quiet sleep. Back to Sleep
campaigns have been in place in many countries since
the early 1990s, and there has been no indication that
supine sleep has lasting negative effects on infant growth
and development. Although supine sleepers are more
likely to attain certain gross motor milestones later than
prone sleepers, this delay is within normal limits and is
no longer apparent at 1 year of age.13–15 In addition, these
differences in motor development are not apparent
when awake “tummy time” is used.16,17"

The infant is awake during Tummy Time so this has no impact on SWS.
Also, they are actually misinterpreting the writing of Dr. Majnemer but
I think I won't even bother to discuss that.

A child isn't asleep during Tummy Time so this does not seem
to address that issue. Also regarding

The PDF:


Larisa Naples, M.S.Ed., Ph.D. said...

Wow! Great brain dump on the Back to Sleep movement. Thanks for the refs.

It seems to me, after reading this, that Peter White was right when he said these are orthogonal issues.

It may be that IFF (math lingo for "if and only if") a particular child has the genetic propensity for SIDS, then the trade-off of slower learning of gross motor skills in exchange for a lower risk of SIDS may be worth it. And certainly, as a policy decision, it makes sense for doctors to advocate that all children be limited to supine sleep, since few parents actually know if their child has that genetic defect, and you don't want to be the pediatrician that says prone sleep is fine, and ends up with a dead patient.

However, the fact that there is no statistical difference between the skills of the population of supine sleepers and the general population after 1 year of age does NOT mean that the individual child who misses out on the REM and NREM sleep cycles for that first year "catches up" to where s/he would have been, given the sleep-consolidation and enhancement of those practiced skills. They would not. In addition, it is unclear to me that ONLY the gross motor skills of infants are at stake. The research I have read on language acquisition (I'll post on this a bit later this fall.) indicates that the learning of abstract concepts is predicated upon mastery of certain basic, gross-motor-skills-related concepts, upon which the more abstract concepts are built. So, if you slow motor-skills development, you may also be slowing cognitive language skills development, which is a depressing thought for the vast majority of kids, who do not have the genetic defect, and are not at risk in the first place.

Honestly, I think there needs to be a lot more research on this.

TSC said...

Dr. Naples, thank you for your comment. I have one other comment regarding the supine sleep position. I apologize for writing so much but heres my thinking about the result of the SIDS Back to Sleep Campaign.

If the reported delays in psychomotor skills, gross motor skills and as you suggested a possible delay in language acquisition skillswhat has actually happened what category would they be put in? Considering that 10% of babies slept on their backs in 1992 and this trended upwards to 76% in 2006 it would probably be a disability that has been increasing during this time period that is characterized by gross motor delays, psychomotor delays, and delays in language acquisition. And if only say 1 out of 100 kids were negatively impacted by back sleep to the extent that it caused them to be considered to have a disability then this would be considered an epidemic considering approximately 4 million infants are born in the U.S. each year. If 1% of 3,000,000 infants (~75% supine sleep rate) born each year became disabled due to the supine sleep position that would mean the U.S. would have an approximately additional 30,000 kids each year that had psychomotor delays, gross motor delays, and language acquisition delays. The only category I think that reasonably fits the negative effects of back sleep and also increased in the 1990's is Autism (PDD-NOS).

The ALSPAC tracks 12,000 infants born in 1990 and 1991 and is where the SIDS Back to Sleep Campaign was essentially started. It tracks both an infants sleep position (in 1990/1991) and whether or not the child was eventually diagnosed with autism. These kids are now between 17 and 18 so I may eventally try the ALSPAC data to prove my hypothesis:


I just posted a paper that was rejected from a number of journals on my blog regarding my thoughts on the SIDS Back to Sleep Campaign as the possible cause of the Autism Epidemic:


Here's an excerpt:

There is a wide range of negative factors associated with the supine sleep position and many of these negative factors overlap with the symptoms of Autism Spectrum Disorders. Thus, “social skills” lags are associated with both autism spectrum disorders and infants who are placed to sleep in the supine position. In addition, speech and language delays are associated with both autism spectrum disorders and the motor skills delays which are associated with the supine sleep position. In addition it has been shown that in infants the supine position causes babies to have more apnea episodes and for a longer duration which has been associated in children to have a negative effect on learning and nonverbal skills. There also seems to be an approximately 4:1 male to female ratio in terms of children with ASD’s64 and a 4:1 male to female ratio for those who have sleep apnea.65 Considering that both the “Back to Sleep” campaign and the increase in ASD’s began in the 1990’s I conjecture that they are associated. Therefore, based upon research studies that show a range of similar negative consequences associated with the supine sleep position and Autism Spectrum disorders, a similar male:female ratio, and that both began increasing in the 1990’s I hypothesize that the American Academy of Pediatrics infant supine sleep recommendations has been a causal factor in the reported increase of Autism Spectrum Disorders, specifically the variant known as Pervasive Developmental Disorders-Not Otherwise Specified (PDD-NOS). In addition, I further hypothesize that the overall gender differences and the severity of the range of symptoms in PDD-NOS can be explained by upper airway anatomical differences between the genders. Future research would need to be done to determine if the increase in reports of ASD’s during the 1990’s and increasing implementation of the supine sleep recommendations during the 1990’sare correlated. Nonetheless, as previously mentioned, the supine sleep position is associated with numerous negative health conditions.

Thanks for your comments.