Total Cognitive Burden

Because it holds some personal resonance for me, my recent round-up of genetic news called to mind food allergies. Now food allergies can be tricky beasts to diagnose, and the reason is, they’re interactive. Maybe you can eat a food one day and everything’s fine; another day, you break out in hives. This is not simply a matter of the amount you have eaten, the situation is more complex than that. It’s a function of what we might call total allergic load — all the things you might be sensitive to (some of which you may not realize, because on their own, in the quantities you normally consume, they’re no or little problem). And then there are other factors which make you more sensitive, such as time of month (for women), and time of day. Perhaps, in light of the recent findings about the effects of environmental temperature on multiple sclerosis, temperature is another of those factors. And so on.

Now, I am not a medical doctor, nor a neuroscientist. I’m a cognitive psychologist who has spent the last 20 years reading and writing about memory. But I have taken a very broad interest in memory and cognition, and the picture I see developing is that age-related cognitive decline, mild cognitive impairment, late-onset Alzheimer’s, and early-onset Alzheimer’s, represent places on a continuum. The situation does not seem as simple as saying that these all have the same cause, because it now seems evident that there are multiple causes of dementia and cognitive impairment. I think we should start talking about Total Cognitive Burden.

Total Cognitive Burden would include genetics, lifestyle and environmental factors, childhood experience, and prenatal factors.

First, genetics.

It is estimated that around a quarter of Alzheimer’s cases are familial, that is, they are directly linked to the possession of specific gene mutations. For the other 75%, genes are likely to be a factor but so are lifestyle and environmental factors. Having said that, the most recent findings suggest that the distinction between familial and sporadic is somewhat fuzzy, so perhaps it would be fairer to say we term it familial when genetics are the principal cause, and sporadic when lifestyle and environmental factors are at least as important.

While three genes have been clearly linked to early-onset Alzheimer’s, only one gene is an established factor in late-onset Alzheimer’s — the so-called Alzheimer’s gene, the e4 allele on the APOE gene (at 19q13.2). It’s estimated that 40-65% of Alzheimer’s patients have at least one copy of this allele, and those with two copies have up to 20 times the risk of developing Alzheimer’s. Nevertheless, it is perfectly possible to have this allele, even two copies of it, and not develop the disease. It is also quite possible — and indeed a third of Alzheimer’s patients have managed it — to develop Alzheimer’s in the absence of this risky gene variant.

A recent review selected 15 genes for which there is sufficient evidence to associate them with Alzheimer’s: APOE, CLU, PICALM, EXOC3L2, BIN1, CR1, SORL1, TNK1, IL8, LDLR, CST3, CHRNB2, SORCS1, TNF, and CCR2. Most of these are directly implicated in cholesterol metabolism, intracellular transport of beta-amyloid precursor, and autophagy of damaged organelles, and indirectly in inflammatory response.

For example, five of these genes (APOE; LDLR; SORL1; CLU; TNF) are implicated in lipid metabolism (four in cholesterol metabolism). This is consistent with evidence that high cholesterol levels in midlife is a risk factor for developing Alzheimer’s. Cholesterol plays a key role in regulating amyloid-beta and its development into toxic oligomers.

Five genes (PICALM; SORL1; APOE; BIN1; LDLR) appear to be involved in the intracellular transport of APP, directly influencing whether the precursor proteins develop properly.

Seven genes (TNF; IL8; CR1; CLU; CCR2; PICALM; CHRNB2) were found to interfere with the immune system, increasing inflammation in the brain.

If you’re interested you can read more each of these genes in that review, but the point I want to make is that genes can’t be considered alone. They interact with each other, and they interact with other factors (for example, there is some evidence that SORL1 is a risk factor for women only; if you have always kept your cholesterol levels low, through diet and/or drugs, having genes that poorly manage cholesterol will not be so much of an issue). It seems reasonable to assume that the particular nature of an individual’s pathway to Alzheimer’s will be determined by the precise collection of variants on several genes; this will also help determine how soon and how fast the Alzheimer’s develops.

[I say ‘Alzheimer’s’, but Alzheimer’s is not, of course, the only path to dementia, and vascular dementia in particular is closely associated. Moreover, my focus on Alzheimer’s isn’t meant to limit the discussion. When I talk about the pathway to dementia, I am thinking about all these points on the continuum: age-related cognitive decline, mild cognitive impairment, senile dementia, and early dementia.]

It also seems plausible to suggest that the precise collection of relevant genes will determine not only which drug and neurological treatments might be most effective, but also which lifestyle and environmental factors are most important in preventing the development of the disease.

I have reported often on lifestyle factors that affect cognitive decline and dementia — factors such as diet, exercise, intellectual and social engagement — factors that may mediate risk through their effects on cardiovascular health, diabetes, inflammation, and cognitive reserve. We are only beginning to understand how childhood and prenatal environment might also have effects on cognitive health many decades later — for example, through their effects on head size and brain development.

You cannot do anything about your genes, but genes are not destiny. You cannot, now, do anything about your prenatal environment or your early years (but you may be able to do something about your children’s or your grandchildren’s). But you can, perhaps, be aware of whether you have vulnerabilities in these areas — vulnerabilities which will add to your Total Cognitive Burden. More easily, you can assess your lifestyle — over the course of your life — in these terms. Here are the sorts of questions you might ask yourself:

Do you have any health issues such as diabetes, cardiovascular disease, multiple sclerosis, positive HIV status?

Do you have a sleep disorder?

Have you, at any point in your life, been exposed to toxic elements (such as lead or severe air pollution) for a significant length of time?

Did you experience a lot of stress in childhood? Stress might come from a dangerous living environment (such as a violent neighborhood), warring parents, a dysfunctional parent, or a personally traumatic event (to take some examples).

Did you do a lot of drugs, or indulge in binge drinking, in college?

Have you spent many years eating an unhealthy diet — one heavy in fats and sugars?

Do you drink heavily?

Do you have ongoing stress in your life, or have experienced significant amounts of stress at some period during middle-age?

Do you rarely engage in exercise?

Do you spend most evenings blobbed out in front of the TV?

Do you experience little in the way of mental stimulation from your occupation or hobbies?

These questions are just off the top of my head, the ones that came most readily to mind. But they give you, I hope, some idea of the range of factors that might go to make up your TCB. The next step from there is to see what factors you can do something about. While you can’t do anything about your past, the good news is that, at any age, some benefit accrues from engaging in preventative strategies (such as improving your sleeping, reducing your stress, eating healthily, exercising regularly, engaging in mentally and socially stimulating activities). How much benefit will depend on how much effort you put into these preventative strategies, and on which and how many TCB factors are pushing you and how far you are along on the path. But it’s never too late to do something.

On the up-side, you might be relieved by such an exercise, realizing that your risk of dementia is smaller than you feared! If so, you might use this knowledge to motivate you to aspire to an excellent old age — with no cognitive decline. We tend to assume that declining faculties are an inevitable consequence of getting older, but this doesn’t have to be true. Some ‘super-agers’ have shown us that it is possible to grow very old and still perform as well as those decades younger. If your TCB is low, why don’t you make it even lower, and aspire to be one of those!

Tips for better sleep

Having trouble sleeping is perfectly normal, especially as we age. It’s estimated that half of those older than 55 have trouble getting to sleep or staying asleep.

What to do if your sleep is poor

Let’s start with the easiest situation: you’re not getting enough sleep because you wilfully go to bed too late to achieve your needs.

This is unfortunately all too common. All I can do is point out how desperately important it is to get the sleep you need. By chronically depriving yourself of sleep, you not only are ensuring that your mental powers are under-par, but you have added significantly to the likelihood that you will develop cognitive problems in old age.

Life is a matter of priorities. To change this situation, you need to give sleep a higher priority than you’ve been doing.

Chances are, though, that your sleep deprivation is not wilful, but is caused by problems in getting to sleep, or staying asleep. If this is the case, you are probably aware of the standard advice, but let me bullet-point it first, before getting to less common solutions.

  • Have a routine
  • Have a regular schedule
  • Get some exercise during the day
  • Don’t do anything too stimulating before going too bed - this includes eating, drinking (caffeine or alcohol), smoking, working, playing games
  • Make sure your room is quiet and dark (wear earplugs and/or a sleep mask, if you can’t do anything about the environment).

Alcohol and sleep

This needs a special mention, because many people see a ‘nightcap’ as an aid to sleep. It’s true that alcohol can shorten the time it takes to fall asleep. It also increases deep sleep in the first half of the night. However, sleep is more disrupted in the second half. While increased deep sleep is generally good, there are two down-sides here: first, it’s paired with sleep disruption in the second half of the night; second, those predisposed to problems such as sleep apnea may be more vulnerable to them. Additionally, at high doses of alcohol, REM sleep is significantly reduced, and in any dose, the first REM period is significantly delayed, producing less restful sleep.

All in all, then, while alcohol may give the illusion of improving sleep, it is not in fact doing so.

Stress & anxiety

Stress and anxiety are of course major factors in chronic sleep problems, and the reason would seem to be the thoughts that plague you.

A good strategy for dealing with this is to write all your worries down, preferably with a planned action. Your planned action doesn’t have to be a solution! It simply needs to be a first step. Write it down, give it a priority rating or action date.

If your worry  is completely fruitless, with no viable action that you can (or want to) take, it’s still worth writing it down, along with its possible consequences. You probably don’t want to think about those consequences, but this is part of why the worry is plaguing you so much. Write down the possible consequences, and their likelihood, and you will get rid of much of their power over you.

Unfortunately, it seems that worriers are not simply more likely to have sleep problems, but they are more affected by them.

A study in which 18 young adults viewed images that were either disturbing or neutral, which were cued by a red minus sign (something horrible coming up!), a yellow circle (don’t worry, nothing disturbing), or a white question mark (you’ll have to wait and see), found that activity in the brain’s emotional centers, the amygdala and insula, rose dramatically when the participant was sleep deprived, with this effect being most extreme when the participant was an anxious type of person.

Sleep deprivation, it appears, has an effect on emotion that is similar to what is seen in anxiety disorders, and those who are naturally anxious are more vulnerable to these effects.

This means that sleep therapy is even more important for the naturally anxious.

How to relax

If you’re prone to stress or anxiety, you’re probably familiar with relaxation techniques. They’re a great idea, but if you haven’t found them as effective as you’d like, the problem may like in the ‘mental churn’ you can’t get rid of. Try the writing strategy first, then follow it up with a relaxation strategy.

If you’ve been unsuccessfully trying a standard relaxation exercise, you may also find a more mentally challenging relaxation strategy works better for you. T’ai chi, for example, is a form of physical meditation that demands your attention, and thus leaves less room for you to fret about your worries. It’s well worth learning for that alone (although it also has physical and mental benefits).

Another less common strategy for dealing with sleep problems is rocking. It does require some expense and effort, given that you need a bed that rocks gently, but it may be worth considering if you’re desperate.

The evidence for this is a little sketchy, unfortunately, but it seems a nice idea, and it certainly seems plausible. A small study involving 12 youngish healthy men found that when they took a 45-minute afternoon nap on a bed that rocked slowly, they went to sleep faster, moved into deep sleep faster, and showed more slow brainwaves and sleep spindles, compared to a similar nap on the same bed, held still. It is a very small sample, and a restricted one, which doesn’t include anyone with sleep problems. But it’s worth noting because apparently every one of the participants showed these effects.

Quiet time

One of the big problems for insomniacs is that typically the more you worry about not being able to get to sleep, the harder it is to fall asleep. Here’s a suggestion: redefine your goal. Why do we need sleep? Because without it we feel lousy the next day; we’re weaker, and we’re less able to think or remember. This is your real goal: giving your mind and body the opportunity to refresh itself.

You need to process the day’s material, to discard what you don’t need, to file what you do need, to wipe the sheet clean so you can start again. Try focusing on that instead.

Lie quietly in your bed. Make sure that it’s quiet and dark. If you find it helpful, you can have gentle music, but not anything that is loud or in any way exciting. Traffic noise, bright light, and temperature extremes, are all common causes of what is termed “environmental sleep disorder”. Moreover, one study found that morning performance on a psychomotor vigilance task was significantly worse if the person had been exposed to traffic noise during the night. Light interferes with circadian rhythms, which are also important for learning and memory.

So, lie there quietly in the dark, and guide your mind through the events of the day. When you come to events of particular interest, focus on them, picking out the details that are important to you. Give the event/information a descriptive label. Pay little attention to events that aren’t worth remembering (you could try mentally dumping them in a trashcan or dumpster). When you’ve run through everything, go back to your labeled sets. (My Memory Journal provides a place and structure for you to do all this.)

IMPORTANT! This is NOT about dwelling on things you need to do! Those should all be in your written list. They’re done.

This is about processing the day’s events and wiping the slate clean for tomorrow.

Let me say again: Bedtime is not, ever, for thoughts of the future.

Nor is it for dwelling on the past, in the sense of emotional wallowing or fretting. What you are doing is housekeeping. You are discarding, filing, and wiping the desk clean.

When you’ve done that, now is your time for your relaxation exercise. Fill your mind with your meditational image; progressively relax your muscles. Whether or not you fall asleep, your aim is to provide the quiet place your mind needs in order to get on with the processing at an unconscious level. You’ve done your bit, giving it the best possible start. Now let it do its job.

Providing a quiet place for your mind to process new information is also an excellent strategy during the day, and this is particularly true for those whose sleep is less than optimal. If you’re learning a new skill or wanting to remember new information, giving yourself 10-15 minutes of quiet reflection (optimally in a darkened environment) helps consolidate it.

If you’re prone to stress-related sleep disturbance, you may also find this strategy useful after any emotionally stressful event.

Sleep and health

It’s a truism that sleep gets worse with age, but a recent study suggests that age may not be the main culprit. The main problem is health - which of course also tends to get worse with age. Medications can cause daytime sleepiness; pain and discomfort can interfere with nighttime sleep.

Weight, too, can be a factor in sleep problems. A study of overweight and obese people found that weight loss improved their overall sleep score by about 20%. Interestingly, the loss of belly fat was particularly useful.

Sleep and diet

Sleep length has also been linked to diet. Data from the very large 2007-2008 National Health and Nutrition Examination Survey (NHANES) found that those who slept 5 to 6 hours a night had the largest calorie intake, followed by those who slept the ‘standard’ 7-8 hours, then those getting less than 5 hours, with those sleeping most (9 hours or more), eating least.

While there were many differences in the make-up of those diets, analysis revealed just a few nutrients that were critically linked to sleep differences. Very short sleep was associated with less intake of tap water, lycopene (found in red- and orange-colored foods, especially tomatoes), and total carbohydrates. Short sleep was associated with less vitamin C, tap water, selenium (found in nuts, meat and shellfish), and more lutein/zeaxanthin (found in green, leafy vegetables). Long sleep was linked to less intake of theobromine (found in chocolate and tea), dodecanoic acid (a saturated fat) choline (found in eggs and fatty meats), total carbohydrates, and more alcohol.

Whether you can change your sleep patterns by changing your diet is as yet unknown, but it is an intriguing speculation.

The role of sleep in memory

Why do we need sleep?

A lot of theories have been thrown up over the years as to what we need sleep for (to keep us wandering out of our caves and being eaten by sabertooth tigers, is one of the more entertaining possibilities), but noone has yet been able to point to a specific function of the sleep state that would explain why we have it and why we need so much of it.

One of the things we do know is that young birds and mammals need as much as three times the amount of sleep as adult birds and mammals. It has been suspected that neuronal connections are remodeled during sleep, and this has recently been supported in a study using cats (Cats who were allowed to sleep for six hours after their vision was blocked in one eye for six hours, developed twice as many new or modified brain connections as those cats who were kept awake in a dark room for the six hours after the period of visual deprivation).

Certainly a number of studies have shown that animals and humans deprived of sleep do not perform well on memory tasks, and research has suggested that there may be a relationship between excessive daytime sleepiness (EDS) and cognitive deficits. A recent study has found that for seniors at least, EDS is an important risk factor for cognitive impairment.

The effect of sleep on memory and learning

Some memory tasks are more affected be sleep deprivation than others. A recent study, for example, found that recognition memory for faces was unaffected by people being deprived of sleep for 35 hours. However, while the sleep-deprived people remembered that the faces were familiar, they did have much more difficulty remembering in which of two sets of photos the faces had appeared. In other words, their memory for the context of the faces was significantly worse. (The selective effect of sleep on contextual memory is also supported in a recent mouse study – see below)

While large doses of caffeine reduced the feelings of sleepiness and improved the ability of the sleep-deprived subjects to remember which set the face had appeared in, the level of recall was still significantly below the level of the non-sleep-deprived subjects. (For you coffee addicts, no, the caffeine didn’t help the people who were not sleep-deprived).

Interestingly, sleep deprivation increased the subjects’ belief that they were right, especially when they were wrong. In this case, whether or not they had had caffeine made no difference.

In another series of experiments, the brains of sleep-deprived and rested participants were scanned while the participants performed complex cognitive tasks. In the first experiment, the task was an arithmetic task involving working memory. Sleep-deprived participants performed worse on this task, and the fMRI scan confirmed less activity in the prefrontal cortex for these participants. In the second experiment, the task involved verbal learning. Again, those sleep-deprived performed worse, but in this case, only a little, and the prefrontal areas of the brain remained active, while parietal lobe activity actually increased. However, activity in the left temporal lobe (a language-processing area) decreased. In the third study, participants were given a "divided-attention" task, in which they completed both an arithmetic and a verbal-learning task. Again, sleep-deprived participants showed poorer performance, depressed brain activation in the left temporal region and heightened activation in prefrontal and parietal regions. There was also increased activation in areas of the brain that are involved in sustained attention and error monitoring.

These results indicate that sleep deprivation affects different cognitive tasks in different ways, and also that parts of the brain are able to at least partially compensate for the effects of sleep deprivation.

Sleep deprivation mimics aging?

A report in the medical journal The Lancet, said that cutting back from the standard eight down to four hours of sleep each night produced striking changes in glucose tolerance and endocrine function that mimicked many of the hallmarks of aging. Dr Eve Van Cauter, professor of medicine at the University of Chicago and director of the study, said, "We suspect that chronic sleep loss may not only hasten the onset but could also increase the severity of age-related ailments such as diabetes, hypertension, obesity and memory loss."

Should we draw any conclusion from the finding that sleep deprivation increased the subjects’ belief that they were right, especially when they were wrong, and the finding that chronic sleep deprivation may mimic the hallmarks of aging? No, let us merely note that many people become more certain of their own opinions as they mature into wisdom.

Is sleep necessary to consolidate memories?

This is the big question, still being argued by the researchers. The weight of the evidence, however, seems to be coming down on the answer, yes, sleep is necessary to consolidate memories — although maybe for only some types of memory. Most of the research favoring sleep’s importance in consolidation has used procedural / skill memory — sequences of actions.

From this research, it does seem that it is the act of sleep itself, not simply the passage of time, that is critical to convert new memories into long-term memory codes.

Some of the debate in this area concerns the stage of sleep that may be necessary. The contenders are the deep "slow wave" sleep that occurs in the first half of the night, and "REM" (rapid eye movement) sleep (that occurs while you are dreaming). Experiments that have found sleep necessary for consolidation tend to support slow-wave sleep as the important part of the cycle, however REM sleep may be important for other types of memory processing.

Sleep studies cast light on the memory cycle

Two new studies provide support both for the theory that sleep is important for the consolidation of procedural memories, and the new theory of what I have termed the "memory life-cycle".

In the first study, 100 young adults (18 to 27) learned several different finger-tapping sequences. It was found that participants remembered the sequence even if they learned a second sequence 6 hours later, and performance on both sequences improved slightly after a night's sleep. However, if, on day 2, people who had learned one sequence were briefly retested on it and then trained on a new sequence, their performance on the first sequence plummeted on day 3. If the first sequence wasn't retested before learning the new sequence, they performed both sequences accurately on day 3.

In another study, 84 college students were trained to identify a series of similar-sounding words produced by a synthetic-speech machine. Participants who underwent training in the morning performed well in subsequent tests that morning, but tests later in the day showed that their word-recognition skill had declined. However, after a full night's sleep, they performed at their original levels. Participants trained in the evening performed just as well 24 hours later as people trained in the morning did. Since they went to bed shortly after training, those in the evening group didn't exhibit the temporary performance declines observed in the morning group.

On the basis of these studies, researchers identified three stages of memory processing: the first stage of memory — its stabilization — seems to take around six hours. During this period, the memory appears particularly vulnerable to being “lost”. The second stage of memory processing — consolidation — occurs during sleep. The third and final stage is the recall phase, when the memory is once again ready to be accessed and re-edited. (see my article on consolidation for more explanation of the processes of consolidation and re-consolidation)

The researchers made a useful analogy with creating a word-processing document on the computer. The first stage is when you hit “Save” and the computer files the document in your hard drive. On the computer, this takes seconds. The second stage is comparable to someone coming and tidying up your word document — reorganizing it and tightening it up.

The most surprising aspect of this research is the time it appears to take for memories to initially stabilize — seconds for the computer saving the document, but up to six hours for us!

See news reports on sleep's role in memory

See news reports on the effects of sleep deprivation

  1. Drummond, S.P.A., Brown, G.G., Stricker, J.L., Buxton, R.B., Wong, E.C. & Gillin, J.C. 1999. Sleep deprivation-induced reduction in cortical functional response to serial subtraction. NeuroReport, 10 (18), 3745-3748.
  2. Drummond, S.P.A., Brown, G.G., Gillin, J.C., Stricker, J.L., Wong, E.C. & Buxton, R.B. 2000. Altered brain response to verbal learning following sleep deprivation. Nature, 403 (6770),655-7.
  3. Drummond, S.P.A., Gillin, J.C. & Brown, G.G. 2001. Increased cerebral response during a divided attention task following sleep deprivation. Journal of Sleep Research, 10 (2), 85-92.
  4. Fenn, K.M., Nusbaum, H.C. & Margoliash, D. 2003. Consolidation during sleep of perceptual learning of spoken language. Nature, 425, 614-616.
  5. Frank, M.G., Issa, N.P. & Stryker, M.P. 2001. Sleep Enhances Plasticity in the Developing Visual Cortex. Neuron, 30, 275-287.
  6. Graves, L.A., Heller, E.A., Pack, A.I. & Abel, T. 2003. Sleep Deprivation Selectively Impairs Memory Consolidation for Contextual Fear Conditioning. Learning & Memory, 10, 168-176.
  7. Harrison, Y. & Horne, J.A. 2000. Sleep loss and temporal memory. The Quarterly Journal of Experimental Psychology, 53A (1), 271-279. Research report
  8. Laureys, S., Peigneux, P., Perrin, F. & Maquet, P. 2002. Sleep and Motor Skill Learning. Neuron, 35, 5-7.
  9. Laureys, S., Peigneux, P., Phillips, C., Fuchs,S., Degueldre, C., Aerts, J., Del Fiore,G., Petiau, C., Luxen, A., Van der Linden, M., Cleeremans, A., Smith, C. & Maquet, P. (2001). Experience-dependent changes in cerebral functional connectivity during human rapid eye movement sleep [Letter to Neuroscience]. Neuroscience, 105 (3), 521-525.
  10. Mednick, S.C., Nakayama, K., Cantero, J.L., Atienza, M., Levin, A.A., Pathak, N. & Stickgold, R. 2002. The restorative effect of naps on perceptual deterioration. Nature Neuroscience, 5, 677-681.
  11. Ohayon,M.M.& Vecchierini,M.F. 2002. Daytime sleepiness and cognitive impairment in the elderly population. Archives of Internal Medicine, 162, 201-8.
  12. Siegel, J.M. 2001. The REM Sleep-Memory Consolidation Hypothesis. Science, 294 (5544), 1058-1063.
  13. Sirota, A., Csicsvari, J., Buhl, D. & Buzsáki, G. 2003. Communication between neocortex and hippocampus during sleep in rodents. Proc. Natl. Acad. Sci. USA, 100 (4), 2065-2069.
  14. Spiegel, K., Leproult, R. & Van Cauter, E. 1999. Impact of sleep debt on metabolic and endocrine function, The Lancet, 354 (9188), 1435-1439.
  15. Stickgold, R., Hobson, J.A., Fosse, R., Fosse, M. 2001. Sleep, Learning, and Dreams: Off-line Memory Reprocessing. Science, 294 (5544), 1052-1057.
  16. Stickgold, R., James, L. & Hobson, J.A. 2000. Visual discrimination learning requires sleep after training. Nature Neuroscience, 3, 1237-1238.
  17. Walker, M.P., Brakefield, T., Hobson, J.A. & Stickgold, R. 2003. Dissociable stages of human memory consolidation and reconsolidation. Nature, 425, 616-620.

Sleep and cognition in children

  • A U.S. survey provides evidence that both children and adolescents tend to be getting less sleep than needed.
  • Depression, lower self-esteem, and lower grades, have all been found to be correlated with sleep deprivation in middle-school children.
  • Sleep disturbance in infants and young children has also been found to be associated with lower cognitive performance.

We all know that lack of sleep makes us more prone to attentional failures, more likely to make mistakes, makes new information harder to learn, old information harder to retrieve ... We all know that, right? And yet, so many of us still go to bed too late to get the sleep we need to function well. Of course, some of us go to sleep early enough, we just can’t get to sleep fast enough, or are prone to waking in the night. (Personally, I can count the times I’ve slept through the night without waking in the last fifteen years on my fingers).

I talk about the effect of sleep on memory elsewhere; I want to talk here about a sleep problem that we don’t tend to think about so much — the sleep deficit children are running.

A survey commissioned by the National Sleep Foundation found that 3-to-6-year-olds in the U.S. get about 10.4 hours sleep nightly, while experts recommend 11 to 13 hours. 1st graders to 5th graders who should be getting 10 to 11 hours are averaging just 9.5 hours.

And a study of middle-school children (11 to 14 year olds) found a direct correlation between sleep deprivation and depression, lower self-esteem, and lower grades. "The fewer hours of sleep that children got, the more depressed they were, the higher number of depressive symptoms [they had], and the lower their self-esteem and the lower their grades."

The second largest growth spurt occurs during these years (usually 10-14 for girls; 11-16 for boys), so this is a time when a lot of sleep is needed. But it’s also a time when children become more capable and more independent; when they’re likely to start taking on a lot more activities, work harder and longer, and are monitored less by their parents and caregivers. So ... it’s not surprising, when we stop and think about it, that a lot of these children are starting to pick up the bad habits of their parents — not getting enough sleep.

Which also points, in part, to the solution: if you’re a parent, remember that your children are, as always, modeling themselves on you. And sleep habits usually reflect a household pattern. If you’re a teacher, remember you need to educate the family, not just the child.

The National Institutes of Health (NIH) have identified adolescents and young adults (ages 12 to 25 years) as a population at high risk for problem sleepiness based on "evidence that the prevalence of problem sleepiness is high and increasing with particularly serious consequences."

Sleep disturbance in infants and young children has also been found to be associated with lower cognitive performance. Previous studies have looked at the severe end of the spectrum of sleep disorders — obstructive sleep apnea. More alarmingly, a new study of 205 5-year-old children found even mild sleep-disordered breathing symptoms (frequent snoring, loud or noisy breathing during sleep) were associated with poorer executive function and memory skills and lower general intelligence.

Before you panic, please note that some 30% of the participants had SBD symptoms, so it’s hardly uncommon (although there may have been a bias towards children with these symptoms; it does seem surprisingly high). You might also like to note that I personally had a blocked nose my entire childhood (always breathed through my mouth, and yes, of course I snored) and it didn’t stop me being top of the class, so ...

Nor is the research yet developed enough to know precisely what the connection is between SBD and cognitive impairment. However, it does seem that, if something can be done about the problem, it is probably worth doing (in my case, taking me off dairy would probably have fixed the problem! but of course noone had any idea of such factors back then).

Here’s a few links that may be of interest to parents and teachers:

The NSF Sleep poll…

a look at the school start times debate (I find this fairly amazing actually, because here in New Zealand, our children usually start school around 9am; the thought of kids starting school at 7.30 sends me into a spin!)

The National Sleep Foundation also has a site for children who want to learn about sleep and healthy sleep habits: For children from 7 up; with educational games and activities, as well as a downloadable copy of NSF’s new Sleep Diary designed especially for children.

This article originally appeared in the November 2004 newsletter.

Subliminal & sleep learning

Subliminal learning achieved notoriety back in 1957, when James Vicary claimed moviegoers could be induced to buy popcorn and Coca-Cola through the use of messages that flashed on the screen too quickly to be seen. The claim was later shown to be false, but though the idea that people can be brainwashed by the use of such techniques has been disproven (there was quite a bit of hysteria about the notion at the time), that doesn’t mean the idea of subliminal learning is crazy.

Ten years ago, researchers demonstrated that subliminal messages do indeed affect human cognition — and showed the limits of that influence [1]. The study demonstrated that, to have an effect on a person’s decision, the subliminal message had to be received very very soon before that decision (a tenth of a second or less), and the person had to be forced to make the decision very quickly. Moreover, there was no memory trace detectable, indicating no permanent record was stored in memory.

But even such brief, low-level learning seems to require some level of attention. A study [2] found that subliminal learning doesn’t occur if the subliminal stimuli are presented during what has been termed an "attentional blink" You may recall when I’ve discussed multi-tasking, I’ve said that we can’t do two things at the same time — that tasks have to "queue" for attention. When a bottleneck occurs in the system, this attentional "blink" occurs.

But low-level sensory processing, which is an automatic process, isn’t affected by the attentional blink, so the finding that subliminal learning is affected by the blink indicates that subliminal stimuli require some high-level cognitive processing.

This finding has been confirmed by other studies. One such study [3] also has implications for reading. Participants in the study were shown either words or pronounceable nonwords and asked to perform either a lexical task (to identify whether the word they saw was a real word or a nonsense word) or a pronunciation task on the words. Unbeknownst to the participants however, they had been first presented with a subliminal word that either matched or didn't match the target word. People performed the tasks faster when the subliminal word was identical to the target word. However (and this is the interesting bit), the researchers then applied a magnetic pulse (transcranial magnetic stimulation) to the key brain regions of the brain before presenting the subliminal information. By applying TMS to one brain area or the other, they found they could selectively disrupt the subliminal effect for either the lexical or pronunciation task. In other words, it seems that, even when the stimulus is subliminal, the brain takes into account the conscious task instructions. Our expectations shape our processing of subliminal stimuli.

Another study [4] suggests that motivation is important, and also, perhaps, that some stimuli are more suitable than others. The study found that thirsty people could be encouraged to drink more, and also pay more for their drink, after being exposed to subliminal smiling faces. Subliminal frowning faces had the opposite effect. However, how much, and whether, the faces had an effect on drinking, depended on the person’s thirst. Those who weren’t thirsty weren’t affected at all. Smiles and frowns are of course stimuli to which we are very responsive.

So clearly, although it is possible to be unconsciously affected by stimuli that can’t be consciously detected, the effect is both small and fleeting. However, that doesn’t mean more long-term effects can’t be experienced as a result of information we’re not conscious of.

Psychologists make a distinction between explicit memory and implicit memory. Explicit memory is what you’re using when you remember or recognize something — it’s what we tend to think of as "memory". Implicit memory, on the other hand, is a concept that reflects the fact that sometimes people act in ways that are clearly affected by earlier experiences they have had, even though they are not consciously recalling such experiences.

Another study [5] that used erotic images (because, like smiling and frowning faces, these are particularly potent stimuli, making it easy to see a response) found that when your eyes are presented with erotic images in a way that keeps you from becoming aware of them, your brain can still detect them — evidenced by the way people respond to the images according to their gender and sexual orientation.

The study is more evidence that the brain processes more visual information than we are conscious of — which is an important part in the process of determining what we’ll pay attention to. But the researchers believe that the information is probably destroyed at an early stage of processing — in other words, as with subliminal stimuli, there is probably no permanent record of the experience.

Which leads me to sleep learning. This was a big idea when I was young, in the science fiction I read — the idea that you could easily master new languages by being instructed while you were asleep.

Well, the question of whether learning can take place during sleep (and I’m not talking about the consolidation of learning that’s occurred earlier) is one that has been looked at in animal studies. It has been shown that simple forms of learning are indeed possible during sleep. However, the way in which associations are formed is clearly altered even for simple learning, and complex forms of learning do not appear to be possible.[6]

As far as humans are concerned, the evidence is that any learning during sleep must occur during the lightest stage of sleep, when you still have some awareness of the world around you, and that what you are learning must be already familiar (presented previously while you were awake and paying attention) and not requiring any understanding.

All the evidence suggests that, although information can be processed without conscious awareness, there are severe limitations on that information. If you want to "know" something in the proper meaning of the word — be able to recall it, think about it — you need to actively engage with the information. No free lunches, I’m afraid!

But that doesn’t mean unconscious influences don’t have important implications for learning and memory. A paper provided online in the Scientific American Mind Matters blog describes how a single, 15-minute intervention erased almost half the racial achievement gap between African American and white students. And this is entirely consistent with a number of studies showing how our cognitive performance is affected by what we think of ourselves (which is affected by what others think of us).

This article first appeared in the Memory Key Newsletter for March 2007

  1. Greenwald, A.G., Draine, S.C. & Abrams, R.L. 1996. Three Cognitive Markers of Unconscious Semantic Activation. Science, 273 (5282), 1699-1702.
  2. Seitz, A. et al. 2005. Requirement for High Level Processing in Subliminal Learning. Current Biology, 15, R753-R755, September 20, 2005.
  3. Nakamura, K. et al. 2006. Task-Guided Selection of the Dual Neural Pathways for Reading. Neuron, 52, 557-564.
  4. Winkielman, P. 2005. Paper presented at the American Psychological Society annual convention in Los Angeles, May 26-29. Press release
  5. Jiang, Y. et al. 2006. A gender- and sexual orientation-dependent spatial attentional effect of invisible images. PNAS, 103 (45), 17048-17052.
  6. Coenen, A.M. & Drinkenburg, W.H. 2002. Animal models for information processing during sleep. International Journal of Psychophysiology, 46(3), 163-175.