Owl Header: Michelle Mathias
Sleep is fundamental to health and has a profound impact on one's mood, immune system, and psychological resilience.
Despite the positive press, sufficiently restful slumber is often the first victim of modern life's hectic schedule. "I'll have plenty of time to sleep when I'm dead" is a delightfully tongue-in-cheek adage, but often disappointingly true.
There are many priorities and distractions that vie for our attention each day. Among work, family, internet, partying, etc., is it any wonder that lying comatose for several hours takes a backseat to far more exciting activities?
After all, sleep is just wasted time. Nothing productive could possibly be going on while I'm asleep, right?
As it turns out, a whole lot of important stuff is happening while you're supposedly lying limp and useless in bed. There are entire scientific journals devoted to the subject, but one particularly vital function of sleep involves: Memory Formation “…[it] is a curious fact, of which the reason is not obvious, that the interval of a single night will greatly increase the strength of the memory… Whatever the cause, things which could not be recalled on the spot are easily coordinated the next day, and time itself, which is generally accounted one of the causes of forgetfulness, actually serves to strengthen the memory.” - Quintilian, circa 35-95 AD (Hammond 2004) It has been apparent for millennia that sleep plays a vital role in memory formation. Though the relationship may have been obvious to ancient scholars like Quintilian, the mechanism itself was beyond their technical understanding. Modern research both describes and reinforces the point.
When something is first experienced, it is "encoded" by the brain. The information is temporarily stored in short-term memory. In order to transition to long-term memory, the encoded memory must be "consolidated," a process of memory stabilization that reduces vulnerability to disruption and deterioration. Degraded memories may also be "reconsolidated" to restore or enhance functionality, as per Quintilian's observation. Sleep is strongly implicated in both of these processes (Walker 2009, Aly & Moskovitch 2010). Without getting too technical, it involves a dialogue between two regions of the brain which can only be sustained during sleep. Getting a bit more technical, this dialogue is regulated by slow-wave oscillations whose amplitude increases proportionally to the amount of information encoded during prior wakefulness (Born 2010). In fact, the neuronal networks that were firing when you first encoded the memory reactivate while you're asleep (Walker 2009), implying that sleep benefits learning by strengthening new neural pathways.
It's even possible to learn new information during sleep without being consciously aware of the process. This is based on a study (Arzi et al. 2012) wherein sleeping subjects were exposed to various odors paired with tones. Once awake, the subjects exhibited an olfactory response (i.e. sniffing) to the tone alone, with the response differing based on the pleasantness of the associated odor. Amazingly, the subjects were not aware of having learned to associate the tones and odors.
So what does this imply about those hours you're "wasting" in peaceful slumber? Only that it's arguably the most important part of the learning process. Check out Harvard University's page on the relationship between sleep and learning. Sleep Deprivation The importance of sleep is readily evident in what happens when we don't get enough of it.
Note that scientific studies divide sleep deprvation into three general categories (Durmer & Dinghes 2005):
Long-term total sleep deprviation: no sleep for >45 hours
Short-term total sleep deprivation: no sleep for <45 hours
Partial sleep deprivation: <7 hours sleep per 24 hour period
Aside from the occasional all-nighter, total sleep deprivation is a relatively uncommon occurance. Chronic partial sleep deprivation is far more likely due to habit, work, study, family, social obligations, etc. There is strong evidence supporting the notion that sleep deprivation detriments are cumulative, meaning that losing just a few hours of sleep per night will eventually result in performance degradation equivalent to total sleep deprivation. Strangely, negative self-assessment of performance and sleepiness increased much slower than cognitive performance, indicating a disjoint between perceived and actual capability under sleep duress (Durmer & Dinghes 2005). So while we may feel only slightly impaired by insufficient sleep, our functional incapacity is likely much greater than it seems.
Despite the positive press, sufficiently restful slumber is often the first victim of modern life's hectic schedule. "I'll have plenty of time to sleep when I'm dead" is a delightfully tongue-in-cheek adage, but often disappointingly true.
There are many priorities and distractions that vie for our attention each day. Among work, family, internet, partying, etc., is it any wonder that lying comatose for several hours takes a backseat to far more exciting activities?
After all, sleep is just wasted time. Nothing productive could possibly be going on while I'm asleep, right?
As it turns out, a whole lot of important stuff is happening while you're supposedly lying limp and useless in bed. There are entire scientific journals devoted to the subject, but one particularly vital function of sleep involves: Memory Formation “…[it] is a curious fact, of which the reason is not obvious, that the interval of a single night will greatly increase the strength of the memory… Whatever the cause, things which could not be recalled on the spot are easily coordinated the next day, and time itself, which is generally accounted one of the causes of forgetfulness, actually serves to strengthen the memory.” - Quintilian, circa 35-95 AD (Hammond 2004) It has been apparent for millennia that sleep plays a vital role in memory formation. Though the relationship may have been obvious to ancient scholars like Quintilian, the mechanism itself was beyond their technical understanding. Modern research both describes and reinforces the point.
When something is first experienced, it is "encoded" by the brain. The information is temporarily stored in short-term memory. In order to transition to long-term memory, the encoded memory must be "consolidated," a process of memory stabilization that reduces vulnerability to disruption and deterioration. Degraded memories may also be "reconsolidated" to restore or enhance functionality, as per Quintilian's observation. Sleep is strongly implicated in both of these processes (Walker 2009, Aly & Moskovitch 2010). Without getting too technical, it involves a dialogue between two regions of the brain which can only be sustained during sleep. Getting a bit more technical, this dialogue is regulated by slow-wave oscillations whose amplitude increases proportionally to the amount of information encoded during prior wakefulness (Born 2010). In fact, the neuronal networks that were firing when you first encoded the memory reactivate while you're asleep (Walker 2009), implying that sleep benefits learning by strengthening new neural pathways.
It's even possible to learn new information during sleep without being consciously aware of the process. This is based on a study (Arzi et al. 2012) wherein sleeping subjects were exposed to various odors paired with tones. Once awake, the subjects exhibited an olfactory response (i.e. sniffing) to the tone alone, with the response differing based on the pleasantness of the associated odor. Amazingly, the subjects were not aware of having learned to associate the tones and odors.
So what does this imply about those hours you're "wasting" in peaceful slumber? Only that it's arguably the most important part of the learning process. Check out Harvard University's page on the relationship between sleep and learning. Sleep Deprivation The importance of sleep is readily evident in what happens when we don't get enough of it.
Note that scientific studies divide sleep deprvation into three general categories (Durmer & Dinghes 2005):
Long-term total sleep deprviation: no sleep for >45 hours
Short-term total sleep deprivation: no sleep for <45 hours
Partial sleep deprivation: <7 hours sleep per 24 hour period
Aside from the occasional all-nighter, total sleep deprivation is a relatively uncommon occurance. Chronic partial sleep deprivation is far more likely due to habit, work, study, family, social obligations, etc. There is strong evidence supporting the notion that sleep deprivation detriments are cumulative, meaning that losing just a few hours of sleep per night will eventually result in performance degradation equivalent to total sleep deprivation. Strangely, negative self-assessment of performance and sleepiness increased much slower than cognitive performance, indicating a disjoint between perceived and actual capability under sleep duress (Durmer & Dinghes 2005). So while we may feel only slightly impaired by insufficient sleep, our functional incapacity is likely much greater than it seems.
The above image is a common search result for "sleep deprivation," so lets do a bit of fact-checking on the listed effects.
Irritability/mood degradation. All three categories of sleep deprivation cause negative mood states, particularly feelings of fatigue, reduced vigor, increased sleepiness, and confusion. Impacts on mood are generally more pronounced than impacts on cognition and motor functionality (Durmer & Dinghes 2005).
Cognitive impairment. The effects are many and well documented. The following list is reproduced verbatim from Durmer & Dinghes (2005):
Impaired (moral) judgment. Sidestepping the arduous task of defining what constitutes "moral" behavior, there is evidence revealing that sleep deprivation does alter one's decision-making priorities. According to Venkatraman et al. (2011), a single night of total sleep deprivation shifts behavior away from "defending against losses" and towards "seeking additional gains." Essentially, risky behavior is more likely to be deemed worthwhile. As an interesting corollary, the report noted that this priority shift was not correlated with the shift in vigilant attention. This means that the increased riskiness of behavior might not be proportional to a one's "sense" of being tired or fatigued.
Hallucinations.
ADHD symptoms.
Diabetes. Sleep deprivation decreases glucose tolerance and insulin sensitivity, with an increase in hunger and appetite that can lead to overeating and weight gain (Spiegel et al. 2005, Knutson et al. 2007), while a single night of sleep deprivation induces insulin resistance in healthy subjects (Donga et al. 2010).
Cardiac risks.
Decreased reaction time. Tomasi et al. (2009) concluded that a single night of sleep deprivation forces the brain to maintain alertness by diverting mental resources from attentional networks usually used to process complex tasks.
Growth suppression.
Irritability/mood degradation. All three categories of sleep deprivation cause negative mood states, particularly feelings of fatigue, reduced vigor, increased sleepiness, and confusion. Impacts on mood are generally more pronounced than impacts on cognition and motor functionality (Durmer & Dinghes 2005).
Cognitive impairment. The effects are many and well documented. The following list is reproduced verbatim from Durmer & Dinghes (2005):
- Involuntary microsleep occurs
- Attention-intensive performance is unstable with increased errors [...]
- Cognitive slowing occurs in subject-paced tasks, while time pressure increases cognitive errors
- Response time slows
- Both short-term recall and working memory performances decline
- Reduced learning (acquisition) of cognitive tasks
- Performance requiring divergent thinking deteriorates
- Response suppression errors increase in tasks primarily subserved by prefrontal cortex
- Increased perseveration [redundant repetition] on ineffective solutions is more likely
- Increased compensatory effort is required to remain behaviorally effective
- Tasks may be begun well, but performance deteriorates as task duration increases
- There is growing neglect of activities judged to be nonessential (loss of situational awareness)
Impaired (moral) judgment. Sidestepping the arduous task of defining what constitutes "moral" behavior, there is evidence revealing that sleep deprivation does alter one's decision-making priorities. According to Venkatraman et al. (2011), a single night of total sleep deprivation shifts behavior away from "defending against losses" and towards "seeking additional gains." Essentially, risky behavior is more likely to be deemed worthwhile. As an interesting corollary, the report noted that this priority shift was not correlated with the shift in vigilant attention. This means that the increased riskiness of behavior might not be proportional to a one's "sense" of being tired or fatigued.
Hallucinations.
ADHD symptoms.
Diabetes. Sleep deprivation decreases glucose tolerance and insulin sensitivity, with an increase in hunger and appetite that can lead to overeating and weight gain (Spiegel et al. 2005, Knutson et al. 2007), while a single night of sleep deprivation induces insulin resistance in healthy subjects (Donga et al. 2010).
Cardiac risks.
Decreased reaction time. Tomasi et al. (2009) concluded that a single night of sleep deprivation forces the brain to maintain alertness by diverting mental resources from attentional networks usually used to process complex tasks.
Growth suppression.
References
Aly, Mariam and Morris Moscovitch. "The effects of sleep on episodic memory in older and younger adults." Memory Volume 18, Issue 3, 2010. http://www.tandfonline.com/doi/abs/10.1080/09658211003601548
Arzi, Anat, Limor Shedlesky, Mor Ben-Shaul, Khitam Nasser, Arie Oksenberg, Ilana S. Hairston, and Noam Sobel. "Humans can learn new information during sleep." Nature Neuroscience Vol. 15, 1460-1465. 2012. http://www.nature.com/neuro/journal/v15/n10/full/nn.3193.html
Donga, Esther, Marieke van Dijk, J. Gert van Dijk, Nienke R. Biermasz, Gert-Jan Lammers, Klaas W. van Kralingen, Eleonara P. M. Corssmit, and Johannes A. Romijn. "A Single Night of Partial Sleep Deprivation Induces Insulin Resistance in Multiple Metabolic Pathways in Healthy Subjects." Journal of Clinical Endocrinology & Metabolism Vol. 95:6, 2963-2968. 2010. http://jcem.endojournals.org/content/95/6/2963.short
Durmer, Jeffrey S. and David F. Dinghes. "Neurocognitive Consequences of Sleep Deprivation." Seminars in Neurology, Vol. 25:1. 2005. http://web2.med.upenn.edu/uep/user_documents/dfd3.pdf
Hammond N. Fragmetary Voices: Memory and Education at Port Royal. Tübingen, Germany: Narr Dr. Gunter; 2004.
Knutson, Kristen L., Karine Spiegel, Plamen Penev, Eve Van Cauter. "The Metabolic Consequences of Sleep Deprivation." Sleep Med. Rev. Vol 11:3, 163-178. June 2007. http://www.ncbi.nlm.nih.gov/pmc/articles/pmc1991337/
Spiegel, Karine, Kristen Knutson, Rachel Leproult, Esra Tasali, and Eve Van Cauter. "Sleep loss: a novel risk factor for insulin resistance and Type 2 diabetes." Journal of Applied Physiology Vol. 99:5, 2008-2019. 2005. http://jap.physiology.org/content/99/5/2008.short
Tomasi, D., R.L. Wang, F. Telang, V. Boronikolas, M.C. Jayne, G.J. Wang, J.S. Fowler, and N.D. Volkow. "Impairment of Attentional Networks after 1 Night of Sleep Deprivation." Cerebral Cortex Vol. 19, 233-240. January 2009.
Venkatraman, Vinod, Scott A. Heutel, Lisa Y.M. Chuah, John W. Payne, and Michael W. L. Chee. "Sleep Deprivation Biases the Neural Mechanisms Underlying Economic Preferences." Journal of Neuroscience Vol. 31:10, 3712-3718. 9 Mar 2011.
Walker, Matthew P. "The Role of Slow Wave Sleep in Memory Processing." J Clin Sleep Med Vol. 5:2Suppl, S20-S26. 15 April 2009. http://www.ncbi.nlm.nih.gov/pmc/articles/pmc2824214/
Arzi, Anat, Limor Shedlesky, Mor Ben-Shaul, Khitam Nasser, Arie Oksenberg, Ilana S. Hairston, and Noam Sobel. "Humans can learn new information during sleep." Nature Neuroscience Vol. 15, 1460-1465. 2012. http://www.nature.com/neuro/journal/v15/n10/full/nn.3193.html
Donga, Esther, Marieke van Dijk, J. Gert van Dijk, Nienke R. Biermasz, Gert-Jan Lammers, Klaas W. van Kralingen, Eleonara P. M. Corssmit, and Johannes A. Romijn. "A Single Night of Partial Sleep Deprivation Induces Insulin Resistance in Multiple Metabolic Pathways in Healthy Subjects." Journal of Clinical Endocrinology & Metabolism Vol. 95:6, 2963-2968. 2010. http://jcem.endojournals.org/content/95/6/2963.short
Durmer, Jeffrey S. and David F. Dinghes. "Neurocognitive Consequences of Sleep Deprivation." Seminars in Neurology, Vol. 25:1. 2005. http://web2.med.upenn.edu/uep/user_documents/dfd3.pdf
Hammond N. Fragmetary Voices: Memory and Education at Port Royal. Tübingen, Germany: Narr Dr. Gunter; 2004.
Knutson, Kristen L., Karine Spiegel, Plamen Penev, Eve Van Cauter. "The Metabolic Consequences of Sleep Deprivation." Sleep Med. Rev. Vol 11:3, 163-178. June 2007. http://www.ncbi.nlm.nih.gov/pmc/articles/pmc1991337/
Spiegel, Karine, Kristen Knutson, Rachel Leproult, Esra Tasali, and Eve Van Cauter. "Sleep loss: a novel risk factor for insulin resistance and Type 2 diabetes." Journal of Applied Physiology Vol. 99:5, 2008-2019. 2005. http://jap.physiology.org/content/99/5/2008.short
Tomasi, D., R.L. Wang, F. Telang, V. Boronikolas, M.C. Jayne, G.J. Wang, J.S. Fowler, and N.D. Volkow. "Impairment of Attentional Networks after 1 Night of Sleep Deprivation." Cerebral Cortex Vol. 19, 233-240. January 2009.
Venkatraman, Vinod, Scott A. Heutel, Lisa Y.M. Chuah, John W. Payne, and Michael W. L. Chee. "Sleep Deprivation Biases the Neural Mechanisms Underlying Economic Preferences." Journal of Neuroscience Vol. 31:10, 3712-3718. 9 Mar 2011.
Walker, Matthew P. "The Role of Slow Wave Sleep in Memory Processing." J Clin Sleep Med Vol. 5:2Suppl, S20-S26. 15 April 2009. http://www.ncbi.nlm.nih.gov/pmc/articles/pmc2824214/
