Lifestyle

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.

I don't think anyone's going to try arguing that fruit and vegetables are not good for your health! We know they're good. But that's just general "oh, I know it's good for me" — do you know that the benefits are not only for your general health, your protection against obesity and diabetes, cancer and heart disease, but also for your brain. Actually, there's two aspects to this. An unhealthy diet (one rich in junk food, in saturated fat and sugar) is actively bad for your brain, and (the right) healthy diet is actively good for your brain.

Fruit and vegetables are only one part of a brain-healthy diet, of course, but they're a very important part. A major reason for this benefit is thought to lie in the antioxidants present in these foods. Antioxidants help fight the oxidative stress that increasingly damages our brain cells as we age. Antioxidants is a group term, and some that fall into this category are more important than others.

The anthocyanins appear to be the most useful — these are responsible for the reds, purples, and blues in some plants. Several studies have affirmed the cognitive benefits of blueberries and Concord grape juice in particular (Concord grapes are especially purple grapes). Basically, the darker the fruit, the more anthocyanins, and the more powerful it will be.

Other valuable compounds include pterostilbene (found in blueberries), and resveratrol (found in grapes and red wine), which lower cholesterol. Quercetin (found in apples, blueberries, and cranberries) protects against cell damage and apparently helps with blood flow.

All of this perhaps explains why it is so much better to eat well rather than hope to receive what you need from dietary supplements!

Of the vegetables, green leafy vegetables, especially spinach, have been found to be especially beneficial. Onions are also a good source of quercetin (and presumably red onions, like red apples, are better than their paler cousins).

As a rule of thumb, the best fruits and vegetables are those with the most color. And, obviously, it's the color you want to eat (so no peeling your nice red apple!).

There have been quite a few studies looking into the possible benefits of omega-3 fatty acids and fish (a good source of the oils), particularly for older adults. Several large studies have found that regular intake of oily fish is associated with lower rates of dementia, and some evidence that eating fish regularly slows the rate of 'normal' age-related cognitive decline.

However, findings into the effects of omega-3 oils have not been consistent, and one reason for that may lie in its interactions with other factors. For example, B vitamins have been found to improved cognition in older adults, but only when omega-3 levels are high. A number of studies have found regular consumption of fish is associated with reduced Alzheimer's risk, but one study found that, although it  was associated with less Alzheimer's pathology, this was only in those with the 'Alzheimer's gene' (APOE4).

The same study found that fish oil supplementation was not associated with any differences in neuropathology — but higher levels of alpha-linolenic acid (an omega-3 fatty acid found in flaxseed, chia seeds, walnuts, etc) were associated with a reduced chance of brain infarctions. Another large study found that omega-3 supplements (fish-based, not plant), together with vitamins C, E, beta carotene, and zinc, had no effect on cognitive decline among older adults with age-related macular degeneration. But it was suggested that this may be because the participants were too old to benefit from them.

Among other groups, the question of whether supplements of omega-3 fatty acids can help memory and cognition has been even more contentious, with some studies showing a positive effect and others failing to find an effect.

My own take on this issue is that, like so many other things, it all depends on what you’re working with. The most important of these factors is surely diet — it would be unsurprising if supplements are only of benefit when the individual's diet is seriously deficient. It may also well be the case that genes are a factor. (I'm ignoring, but we shouldn't forget, that many of the studies are probably poorly done, for this is a problematic area and it is tricky to do well.) There does seem to be more evidence that a diet high in omega-3 oils is good, than that supplements are going to help. And the weight of the evidence certainly favors the importance of high omega-3 levels for older adults.

Although it's not yet clear which fatty acids are most important, one is definitely docosahexaenoic acid, or DHA. Salmon, mackerel, herring, sardines, and anchovies are all good sources (not, I am sorry to say, your standard fried fish from the chippie). Other sources include almonds, walnuts, soy, flaxseed oil, and eggs laid by chickens that eat DHA-supplemented feed.

 

 

There hasn't been a lot of research into the effects of herbs and spices on cognition and the brain, unfortunately. But on the positive side, the risk of side-effects is very low, so we don't need a lot of evidence for it to be worth trying.

Spices

Probably the most researched of these substances is the curry spice turmeric, more specifically one of its components, called curcumin. This has been found to be a powerful antioxidant and anti-inflammatory, which affects the brain protein BDNF (involved in the creation of new neurons). Research also suggests it may be protective against amyloid plaques, and so help fight Alzheimer's.

These findings have had an effect on my own cooking — I habitually cook up a lot of vegetables in the wok for our evening meal, and I add turmeric to the mix (heating it, along with some other curry spices, in the oil before adding the veges), so I have turmeric most days. Cumin, by the way, is (notwithstanding the similarity in names) something completely different.

Another spice that may be helpful, and one that is even easier to add to your daily diet, is cinnamon. I’ve been happily generous with cinnamon on my breakfast ever since the first hints came out that cinnamon might help protect against Alzheimer’s (it’s not like it’s an ordeal to add cinnamon!). Now we have more evidence, with a finding that two compounds found in cinnamon —cinnamaldehyde and epicatechin — appear to help prevent tau tangles (one of the characteristics of Alzheimer’s).

Herbs

As for herbs, there's a researcher in Britain who takes an interest in herbs, and it's really solely down to him and his students that we have any idea about the effects of herbs on cognition. Because they're all from one lab, and because the studies are invariably quite small, and the issue difficult to study, we can't put too much weight on these findings. But, as I say, where's the harm?

Four herbs have been put forward as helpful for the brain. Sage and lemon balm seem to increase the activity of acetylcholine, and so may be helpful to protect against Alzheimer's. They have also been linked to better cognitive performance. The scent of rosemary (i.e. from essential oil) has also been linked to better cognition, as has drinking peppermint tea.

From a more indirect perspective, chamomile tea and the scent of lavender have both been linked to feelings of calmness, which might help those who suffer from sleep problems. Lemon balm has also been linked to greater feelings of calmness.

Let me start by saying that if you're healthy and are eating a good balanced diet, there should be no need for you to take supplements. I also want to emphasize that the best way of meeting your body's needs for certain vitamins and minerals is to get them from food. In some cases, for one reason or another, this may not be possible. For example, as a (mostly) vegan, I take iron and B12 supplements, to make up for these deficiencies in my diet. Elderly adults with small appetites may also find it hard to get all the nutrients they need from their diet.

What nutrients are important for brain health and cognition?

Minerals

Number one mineral for cognition, that goes right across the age groups, is iron. A number of studies have found that iron deficiency in children and adolescents is associated with lower scores of cognitive tests, and indeed, it may be that iron deficiency during infancy has long lasting effects on cognition. The effects on adults have been less studied, but there is some evidence that iron deficiency may be linked to poorer attention. What's worth noting is that the levels at which iron is "deficient" may be overstated. It now seems that negative effects occur long before a person is officially diagnosed with anemia.

Other minerals that may impact learning and memory are magnesium and zinc, although evidence is limited thus far. Magnesium deficits are common in industrialized countries, and increase with age. Vegetarians, adolescents, and older adults, are particularly at risk of zinc deficiency. An analysis of Alzheimer's has revealed that one type of the disease, which is found most commonly at a younger age (50- to early 70s) and typically shows itself first in language and number difficulties, is associated with a significant zinc deficiency.

Good sources of magnesium are dark green leafy vegetables, some nuts (especially almonds and cashews), beans, seeds and whole unrefined grains (especially buckwheat). Red meats, fish and grains are good sources of zinc.

Do bear in mind that it is not a case of "if some is good, more is better"! Having too much is not a good idea either; this is another reason why getting your vitamins and minerals from food rather than supplements is a good idea. Too much iron, in particular, has been linked to an increased risk of Alzheimer's. It has been argued that many neurodegenerative diseases are partly caused by poorly bound iron, and it is vital to consume nutrients which bind iron, such as brightly-colored fruits (especially purple) and vegetables — but not, perhaps, green tea, which does bind iron, but taking them at the same time seems to cancel out each other's benefits!

Just to complicate the matter further, there is evidence that zinc inhibits iron absorption. These complications suggest there is something in the idea that you need to consider food combinations.

Vitamins

Vitamins B, C, D, and E all seem to be important for cognition, mainly in relation to prenatal development and prevention of Alzheimer's and age-related cognitive impairment. A long-running study of older adults found that those with diets high in omega 3 fatty acids and in vitamins C, D, E and the B vitamins had higher scores on cognitive tests than people with diets low in those nutrients, and moreover that these were dose-dependent, with each standard deviation increase in the vitamin BCDE score ssociated with an increase in cognitive score. Additionally, they showed less brain shrinkage than those with lower intakes of these nutrients.

The B vitamins are often called the B-complex vitamins, and they are a messy sort of group. The main ones of interest for cognition are B12, folate, and choline. Again, most of the research has focused on prenatal development, and age-related cognitive impairment and dementia.

The importance of folate and B12 has a lot to do with homocysteine, which is produced in the body by the breakdown of a dietary protein called methionine. High levels of homocysteine have been linked to increased risk of Alzheimer's, stroke, and vascular dementia, and greater brain shrinkage. B-vitamins are required to convert homocysteine back to methionine, and high levels of homocysteine go hand in hand with low levels of B12 and folate. Diet isn't the only reason for increased levels of homocysteine; smoking has also been implicated. But the association between homocysteine and age-related cognitive decline is not straightforward — it appears that seniors with normal levels of vitamin B12 perform better if their folate levels are high, but when vitamin B12 is low, high levels of folate were associated with poor cognitive performance, as well as a greater probability of anemia. Vitamin B12 is often deficient in older people.

There is also some evidence that B12 is more effective in slowing cognitive decline if levels of omega-3 oils are high.

Folate is a water-soluble B vitamin found particularly in citrus fruit, green leafy vegetables, whole-wheat bread, water-soluble dried beans and peas; however, they are often destroyed by cooking or processing. In the United States, Canada and Australia, flour is fortified with folic acid. Vitamin B12 is naturally found in animal foods including fish, milk and milk products, eggs, meat, and poultry.

Among older adults, choline, particularly in conjunction with omega-3 fatty acids and uridine (not available from food), has been found to improve memory in those cognitively impaired. Top sources of choline are eggs, peanuts, and meat. Fish and soy are also good sources.

I’ve always been interested in the body’s clocks — and one of the most interesting things is that it is clocks, in the plural. It appears the main clock is located in a part of the brain structure called the hypothalamus (a very important structure in the brain, although not one of much importance to learning and memory). The part of the hypothalamus that regulates time is called the suprachiasmatic nuclei. These cells contain genes that switch on, off, and on again over a 24-hour period, and send electrical pulses and hormones through the body. This is the body’s master clock.

But it is not the only clock in the body. Each organ in the body uses the time signal from the master clock to set its own clock. As a consequence, different systems in the body operate on different schedules. Thus blood pressure peaks at one particular time of the day, and levels of the stress hormone cortisol rise and fall in accordance with the clock that governs this.

The effect of this is that certain physical disorders are more likely to occur at particular times, and, more significantly, that certain medications may be far more effective at certain times.

What does all this have to do with learning and memory?

Well, not a whole lot of research has been done on the effects of time of day on cognitive performance, but what has been done is reasonably consistent. It seems clear that, for many people (but not all), there are significant time of day effects. The most reliable is that, in general, teenagers and young adults perform best (mentally) in the afternoon, while older adults (seniors) perform best in the morning.

Having said that, let’s qualify it a little.

Let’s start with a table. Now, this represents the findings of one study [4], so let’s not get carried away with the illusion of precision cast by actual numbers. Nevertheless, it is interesting. These percentages represent the preferences reported by the young and old participants in the study. These preferences correlated with improved performance on a memory test.

	Young	Old
Definite morning	0%	34%
Moderate morning	8%	49%
No preference	57%	10%
Moderate evening	29%	6%
Definite evening	6%	1%

Now the first thing to note is how marked the differences are between young and old. Of particular interest is how many of the younger adults had no preference. Compare this with that of older adults. The second finding of particular note is how pronounced the preference for the morning is in older adults — 83% preferred morning. And, most interesting of all, is a finding from another study by the same researchers [5]: when tested at their preferred time, older adults performed comparably to younger adults on a memory task. Younger adults, by contrast, seem able to perform well at all times.

There is also some evidence [3] that the deleterious effect of interference (the intrusion of irrelevant words, objects, events) is worse for older adults at those times of day when their performance is poorer. Older adults are more vulnerable to interference than younger adults.

The findings for teenagers and young adults may also apply to children. One study [2] found that below-grade-level students who received reading instruction in the afternoon improved their performance more than those students who received instruction in the morning.

But it must always be remembered that this general principle that morning is better for the aged, and afternoon better for the young, does not apply to each and every individual. As the table tells us, time of day affects some people more than others, and time preference is an individual matter, not entirely predicted by age. This is underscored by a study [1] that found improved performance when students were taught at times that matched their preferences. There was also some evidence that, for some students at least, achievement was greater when they were taught during their teacher's ideal time of day.

None of this is an argument that you should resign yourself to learning only at your preferred time of day! But you could use the information to modify your strategies. For example, by scheduling difficult work for your optimal time (assuming you have an optimal time, and are not one of those fortunate people who have no strong preference). You can also try and counteract the effect by, for example, drinking coffee during your nonoptimal time of day (this was found to be effective in one study with older adults [6]).

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