Lesson 14c. Memorize While You Sleep

Get enough sleep to consolidate your memories.

Did you know that your brain works while you sleep? Yes, both during dreaming and non-dreaming, your brain is consolidating memories of events in the immediately preceding day.

Most people think that the purpose of sleep is to rest the brain. But there is clear evidence that the brain is still busily at work during sleep, even when the brain is not dreaming. Decades ago, researchers demonstrated that many neurons fired just as much during sleep as during wakefulness. Some neurons were even more active during sleep.

One advantage that sleep provides for memory consolidation is that the brain doesn’t have all the distractions that occur during daytime wakefulness. Multiple-conflicting stimuli and tasks are very disruptive to memory consolidation.

The advantages offered by having fewer disruptive influences during sleep have also been confirmed in a study conducted in the brain imaging lab of Thomas Pollmacher in Munich, Germany. An auditory text stimulus was presented to sleep-deprived subjects prior to and after the onset of sleep, and imaging was performed to compare wakeful responses to sound stimuli with those during various stages of non-dreaming sleep. Brain activity during sleep was suppressed in auditory pathways and visual cortex, including other brain regions that are interconnected with the visual cortex. Suppression suggests that sleep shields the brain from the arousing effects of external stimulation that might disturb sleep. Blocking out such interference effects should facilitate memory consolidation. This study also prompted researchers to conclude that consolidation of memory occurs over many hours, at least in sleep-deprived subjects. That is to be expected, inasmuch as consolidation of memory depends on protein synthesis and physical changes in synapses.

Students often cut back on sleep to finish ever-mounting piles of homework and study. Combat soldiers are trained to function under sleep-deprived conditions. But these strategies are likely counter-productive. At my university, our Corps of Cadets used to have a tradition of rousing freshmen in the middle of the night and preventing them from sleeping. The idea was to make them tough. More likely, it just made them unable to do well in school, as I have seen many of them flunk out.  Another area where this problem has surfaced is with sleep-deprived medical residents.

Sleep loss degrades many brain functions. In one study, sleep loss degraded visual vigilance and memory for words, and time-of-day fluctuations were found in choice reaction time, logical reasoning, and word memory. Exercise also seemed to have an effect in that brain function of non-exercising subjects degraded sooner than they did for exercising subjects. So, sleep-deprived couch potatoes beware!

Researchers have found that people who stay up all night after learning and practicing a new task show little improvement in their performance. No amount of sleep on following nights can make up for the toll taken by the initial all-nighter.

Robert Stickgold and colleagues at Harvard Medical School report that people who learned a particular task did not improve their performance when tested later the same day but did improve after a night of sleep. To see whether the night of sleep actually caused the improvement, Stickgold trained 24 subjects in the same visual discrimination task, which consisted of identifying the orientation of three diagonal bars flashed for a sixtieth of a second on the lower left quadrant of a computer screen full of horizontal stripes. Half of the subjects went to sleep that night, while the other half were kept awake until the second night of the study. Both groups were allowed to sleep on the second and third nights. On the fourth day, both groups were tested on the visual discrimination task. Those who slept the first night identified the correct orientation of the diagonal bars much more rapidly than they had the first day. The other group showed no improvement, despite the two nights of catch-up sleep.

Another compelling study for the role of sleep on memory consolidation was published by Sean Drummond and his colleagues at San Diego State University and the University of California, San Diego.  They combined memory performance with magnetic resonance imaging (MRI) to study sleep deprivation effects on verbal learning of young, healthy adults. After a sleepless night, free recall fell by about half, and the brain imaging analysis showed reduced blood oxygen activity in the temporal area. However, the areas of the prefrontal cortex that had been activated during remembering after normal sleep worked even more after sleep deprivation. What's more, the bilateral parietal lobes and two additional areas in the prefrontal cortex, usually not activated after normal sleep, became active.

What about a small degree of sleep loss? A University of Pennsylvania study showed even a little sleep loss can devastate memory. People were assigned to sleep regimens of four, six, or eight hours of sleep each night for two weeks and tested periodically during the daytime for mental performance. Subjects who got four or even six hours of sleep performed as poorly on brain function tests as they did when kept from sleeping at all for three consecutive days. So, short-changing your sleep each night by an hour or so builds up a sleep debt that affects attention and working memory. In the study, performance decline was cumulative. An interesting aside from the study was that none of the 48 people in the study realized that their mental performance had deteriorated from the mild sleep loss. As a college professor, I wonder about the performance loss going on in students who short-change their sleep for months at a time.

There are also studies revealing lack of sleep BEFORE learning interferes with memory. Formally, this is called "proactive interference," because it occurs in advance. The cause may relate to what was just explained: a sleepy brain doesn’t think effectively.

In another study, 28 healthy young adults were divided into two groups. On the first day, one group was kept awake for 35 straight hours. Participants in the other group spent a normal sleep night at home. At 6 PM of the next day, all subjects watched a slide show of 150 slides of landscapes, objects, and people who weren't celebrities. All subjects then were sent home to have a normal night's sleep. The next evening all subjects took a pop quiz on the slides, which were randomly mixed with 75 new slides. The test was for subjects to recognize whether they had seen each slide before.

Those subjects who had been sleep deprived on the first night scored the lowest, even though they later had a night to catch up on lost sleep. The upshot of it all is that lack of sleep is bad for remembering, whether the sleep loss occurs before or after learning events. For those who wonder why humans need to sleep, one obvious benefit is to enhance learning.

Need to learn something quickly? Take a nap. Daytime naps are said to rejuvenate energy and lower stress. Now there is evidence naps speed up consolidation of memories.

Matthew Walker reports experiments showing nap enhancement of memory. In his study, 39 young adults were divided into two groups. At noon, all the participants took part in a memory exercise that required them to remember faces and link them with names. Then the subjects took part in another memory exercise at 6 p.m., after 20 subjects had napped for 100 minutes during the break. Those who remained awake performed about 10 percent worse on the tests than those who napped. Students take note: 10% is often the difference between an A and a B.

 

Sleep Sources

Drumond, Sean, Brown, Gregory, G., Gillin, J. Chrisstian, Stricker, John. L. (2000). Altered brain response to verbal learning following sleep deprivation. Nature 403(6770):655-7. DOI: 10.1038/35001068

Stickgold, R., James, L, and Hobson, J. (2000) Nature Neuroscience.  3 (12), 1237-1238. DOI:10.1038/81756

Van Dongen, H.P.A., Rogers, N.L. & Dinges, D.F. Sleep debt: Theoretical and empirical issues. Sleep Biol. Rhythms 1, 5–13 (2003). https://doi.org/10.1046/j.1446-9235.2003.00006.x

Walker, Matthew (2010). American Association for the Advancement of Science annual meeting presentation, San Diego, Feb. 21, 2010.

 

This concludes our lessons in this series on Learning How to Learn.

I believe and hope that you all will become more effective life-long learners.

 

Flushing the Brain While You Sleep

I had written before about the breakthrough in studies of mice that showed lymphatic  flushing of brain tissue in mice while they slept. Now this phenomenon has been confirmed in humans. During human sleep, pulses of cerebrospinal fluid (CSF) flush throughout the brain. You can see a spectacular real-time video at this site: https://www.sciencealert.com/mesmerising-video-shows-waves-of-spinal-fluid-washing-over-the-brain-during-sleep.

Midline brain scan showing flushed area in red at one instant, pulsing at about 1-2 times/sec. From Fultz, 2019.

Interestingly, the flushing seems to include most of the brain, except the brainstem and the cerebellum. These CSF waves presumably flush out unnecessary proteins and other redundant debris. It is likely that the microtubule lymphatic-like system inside of brain tissue that opens during deep sleep is part of the CSF circulatory system. CSF is generated in specialized regions of the cerebral ventricles and ultimately drains back into the bloodstream.

Another research group simultaneously reported in the same issue of Science that cerebral blood flow diminishes by about 25% during slow-wave sleep, and apparently this facilitates an increase in the volume of CSF that can flow through the brain.

Another research group simultaneously reported in the same issue of Science that cerebral blood flow diminishes by about 25% during slow-wave sleep, and apparently this facilitates an increase in the volume of CSF that can flow through the brain.

The CSF pulsing is associated with slow-wave pulsing in the field potentials (as seen in EEGs, for example) generated by brain during the initial stages of sleep. The electrical waves and CSF pulses are coincident in a shared rhythm. The amount of slow-wave electrical activity diminishes in most elderly, and this may be a cause of dementia, which results from accumulated metabolic waste products. Sleep clinics could easily determine the amount of slow-wave sleep and thus perhaps detect early warning signs of impending dementia. Research on drugs and sleep habits that promote slow-wave EEGs might forestall and even treat dementia.

Sources:

Fultz, Nina E. et al. 2019. Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science. 366(6465), 628-631. doi: 10.1126/science.aax5440

Grub, Søren and Lauritzen, M. 2010. Deep sleep drives brain fluid oscillations. Science. 366(6465), 572-573. DOI: 10.1126/science.aaz5191

Sleep Is Good for Your Heart

What are you doing to prevent a heart attack? Perhaps you do the things cardiologists typically recommend: exercise, eat less saturated fat, take statins and omega-3 supplements. Now, there is another recommendation: get 6-9 hours high-quality sleep each night.

One recent report of over 400,000 people who were evaluated over seven years  revealed that people who slept 6-9 hours a night had a 20% lower risk of a heart attack than people who slept less. However, sleeping more than 9 hours had a 34% higher risk.

Napping also seems to be a good idea. A group in Switzerland just reported from 3,462  people that

Source: Unsplash.com

those who had two or more naps a week had significantly less cardiovascular disease than those who did not nap. The benefit was unrelated to the length of napping.

The reason sleep is beneficial has not been established, but two lines of reasoning could explain it. The heart gets a rest during sleep. Heart rate and blood pressure typically go down during sleep. Also, sleep gives us a break from the stressful events of the day, events which release hormones and activate the "fight or flight" system that put a strain on the heart.

As to the paradox of the harmful effects of too much sleep (> 9 hours), one possible cause is too much dreaming, which is tied to the amount of sleep. During dreaming, blood and heart rate can spike, depending on the nature of what one is dreaming about.  The incidence of unpleasant, and therefore stressful, dreams should increase with increasing amounts of sleep time. By the way, I published a theory that asserts that the purpose of dreaming is the brain’s way to tell itself it has had enough sleep and it is time to wake up.

Another cause of excessive sleep can be poor quality sleep. For example, insomniacs may need more sleep because they are not getting enough of good, restful sleep.

Sleep apnea is a proven cause of bad sleep. Apnea is extremely stressful and can raise blood pressure on a continual basis, even during wakeful hours.

So, sleep well, with pleasant dreams. If your dreams are disturbing, program your brain to stop that. Tell your brain its job is to nurture you, not beat up on you. See my Psychology Today post on "How Nightmares May Affect Us, and What We Can Do about It."

Sources:

Daghlas, I. et al. (2019). Sleep duration and myocardial infarction. J. Amer. College of Cardiology. 74, 1304-1314.

Häusler, N. et al. (2019). Association of napping in incident cardiovascular events in a prospective cohort study. Heart. doi: 10.1136iuheartjnl2019-314999 (Sept. 9)

Klemm, W. R. 2011. Why does REM sleep occur? A wake-up Hypothesis. Frontiers in Neuroscience. 5 (73): 1- 12. Doi: 10.3389/fnsys.2011.00073

Two New Discoveries to Explain Why Exercise Is Good for You

Have you noticed that so many elderly people seem frail, walk slowly, and seem to lack energy? If this applies to you, noticing it is unavoidable. These problems are preventable. For 25 years, I jogged at least a mile and a half three times a week. This was crucial for helping me stop smoking. I don’t know why, except that I could not smoke and jog at the same time. Also, the 15-30 minute recovery time reminded me just how bad the smoking had been for my health.

Why did I quit jogging? The jogging messed up my joints. So, I took up swimming, but since I sink like a lead mannequin, that is just too much work. So now, I joined a gym, where I use the elliptical, treadmill, and muscle-building machines. This environment helps because I have companions in my discomfort, and occasionally I get the satisfaction of comparing myself to the few “90-pound weaklings” that show up.

We have known for many years that exercise is good for you, especially as you get older. Known benefits of exercise include:

• Relieve stress and promote a sense of well being. (Well, at least after the soreness wears off).
• Improve heart and cardiovascular function. (If the damage is already done, don’t expect huge improvements).
• Lose weight. (Pushing away from the table is the best exercise for this effect).
• Strengthens bones. (Reduces loss of bone density in old age. But high-impact exercise may damage joints).
• Lower blood sugar and help insulin work better.
• Help quit smoking. (Ever try to smoke while jogging? Ha!).
• Improve mood and resist depression. (Ever heard of “runner’s high? It comes from release of endogenous opiates).
• Releases proteins and other chemicals that improve the structure and function of your brain. (Memory ability improves too).
• Improve your sleep. (I mean, besides making you really tired. To reduce interference from soreness, take acetaminophen before bed time).\
• Reduce your risk of some cancers, including colon, breast, uterine, and lung cancer.

What was not as well known until recently was the effect of exercise on the immune system. Recent research indicates that exercise in older age can prevent the immune system from declining and protect people against infections. A recent study followed 125 long-distance cyclists, and found that some of those in their 80s had the immune systems of 20-year olds. Maybe this is a reason exercise can help prevent cancer.

The key indicator was the level of T-cells in the blood. T cells, named after the thymus where they first appear, are a type of white blood cell that makes antibodies. As people age, the thymus gland, located in the neck, shrinks and T-cell activity resides mostly in bone marrow. The study of cyclists revealed that they were producing the same level of T-cells as 20-year olds, whereas a comparison group of inactive older adults were producing very few. Thus, it would seem that, though not tested in this study,   physically active seniors would also respond better to vaccines than sedentary people.

The other new discovery is the importance of exercise on brain white matter integrity. White matter electrically insulates nerve fibers, which has two effects: 1) speeds communication in neural networks and 2) reduces “cross talk” among adjacent fibers. The study compared people averaging 65 who were mentally normal and those who had mild cognitive impairment, which is a risk factor for later development of Alzheimer’s Disease. In both groups, investigators measured cardiovascular function with a standard measure of heart and respiratory fitness, the VO2 Max test. They also used brain scans to measure white matter integrity. Levels of physical activity were positively associated with white matter (WM) integrity and cognitive performance in normal adults and even in patients with mild cognitive impairment.

Given all this, how much more reason do you need to get off the couch and start moving? Besides, at the end of a good workout, it feels so good to quit.

*****

"Memory Medic's latest book is for seniors: "Improve Your Memory for a Healthy Brain. Memory Is the Canary in Your Brain's Coal Mine," available in inexpensive e-book format at https://www.smashwords.com/books/view/496252.  See also his recent books, "Memory Power 101" (Skyhorse), and "Mental Biology. The New Science of How the Brain and Mind Relate" (Prometheus).

*****

Sources:

Ding, Kan, et al. (2018).Cardiorespiratory fitness and white matter neuronal fiber integrity in mild cognitive impairment. Journal of Alzheimer's Disease, 61(2), 729-739.

Duggai, Niharika A. et al. (2018). Major features of immune senescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood. Aging Cell. 8 March. 

https://doi.org/10.1111/acel.12750.

https://medlineplus.gov/benefitsofexercise.html

Sleep Needed for Memory

Got kids or grandkids in school? Odds are they are not getting enough sleep, and it is hurting their learning and grades. This is a special problem for older adolescents. At this age, the biological clock shifts and makes them stay up too late if they need to get up at 6-7 A.M. to get ready for school. Kids this age need about 9 hours of sleep a night. So what is the relationship to learning? Two things:

1. When students are drowsy during class, they can't focus attention and will not encode new information effectively. Sometimes they even fall asleep in class, which means they are not encoding anything.

2. Sleep provides an uninterrupted mental environment in which the brain rehearses the events of that day. As documented in dozens of peer-reviewed research reports, this rehearsal promotes consolidation of fragile temporary memory into more permanent form.

Now, two new studies reveal what happens during sleep to accomplish this consolidation task. Just as a computer writes to a hard drive or CD for permanent storage, the brain has to have a storage mechanism. Information in the brain resides, in real time, in the form of nerve impulses flowing around in certain networks. As long as the impulses are present, the memory is present. But if the impulse patterns change, then the information they represented is lost—unless the impulse pattern was played long enough to cause structural change in the corresponding circuitry. Scientists have known for several decades that information is stored in the junctions (synapses) between neurons. We used to think that the synapses involved in learning can grow from repeated use. Impulse patterns representing the day's experiences are replayed during sleep, providing the repetition needed to stimulate growth in the corresponding synapses. But new evidence suggests that learning does not cause the involved synapses to grow, but rather prunes them during sleep to remove irrelevant information.

One of the new studies showed that synapses in mice change structure and chemistry during sleep. In sleep, the synaptic gaps become narrower and the number of neurotransmitter receptors decreases. This may constitute a pruning process. Synapses receive multiple inputs, and a pruning process could help remove irrelevant and interfering information, thus causing a relative magnification of the memory of information being rehearsed during sleep. Another way to think about it is that sleep may provide a mechanism for "smart forgetting."

The second study by another group, also in mice, confirmed this evidence of pruning and further implicated a particular receptor, the one for the excitatory neurotransmitter, glutamate. The investigators even identified the gene that is activated to remove excess glutamate receptors.

The practical application of these findings for school children is that the more they are allowed to sleep, the more time there is for sleep to cause the synaptic changes needed to store the day's learning in the "brain's hard drive." The other, more general, implication of these studies is that the brain's anatomy and physiology are readily changed by experience, a well-established fact that scientists call "neural plasticity."

Readers may be interested in "Memory Medic's" book, Memory Power 101 (Skyhorse) and his more recent book, Mental Biology (Prometheus).

Sources:

de Vivo, Luisa, et al. (2017). Ultrastructural evidence for synaptic scaling across the wake/sleep cycle. Science.  355, 507-510.

Diering, Graham H. et al. (2017). Homerla drives homeostatic scaling-down of excitatory synapses during sleep. Science. 355, 511-515.

Sleep Away Your Bad Attitudes

Generally speaking, you cannot learn from sounds of new information while you sleep, though this was a fad several decades ago. But in an earlier post, I discussed a new line of research where sleep learning can occur. The key is to play sound cues that were associated with learning that occurred during the previous wakefulness period. The explanation I posted was that cue-dependent sleep learning can work because a normal function of sleep is to strengthen memories of new information and that presenting relevant cues during sleep increases the retrieval of these memories and makes them accessible for rehearsal and strengthening.

The latest experiment by a different group shows that this cuing during sleep can modify bad attitudes and habits. The test involved counter stereotype-training of certain biased attitudes during wakefulness, and investigators reactivated that counter-training during sleep by playing a sound cue that had been associated with the wakefulness training.

In the experiment, before a 90-minute nap 40 white males and females were trained to counter their existing gender and racial biases by counter-training. A formal surveyed allowed quantification of each person's level of gender or racial bias before and after counter-training. For example, one bias was that females are not good at math. Subjects were conditioned to have a more favorable attitude about women and math with counter-training that repeatedly associated female faces with science-related words. Similarly, racial bias toward blacks was countered by associating black faces with highly positive words. In each training situation, whenever the subject saw a pairing that was incompatible with their existing bias they pressed a "correct" button, which yielded a confirmatory sound tone that was unique for each bias condition. Subjects were immediately tested for their learning by showing a face (female or black) and the counter-training cue, whereupon they were to drag the appropriate bias-free face on to a screen with the positive word. For example, if the first test screen was that of a woman, accompanied by the sound cue, the subject dragged a woman's face onto a second screen that said "good at math." Results revealed that this conditioning worked: both kinds of bias were reduced immediately after counter-conditioning.

Then during the nap, as soon as EEG signs indicated the presence of deep sleep, the appropriate sound cue was played repeatedly to reactivate the prior learning. When subjects re-took the bias survey a week later, the social bias was reduced in the sound-cued group, but not in the control group that was trained without sound cues.

Experimenters noted that the long-term improvement of bias was associated with rapid-eye-movement (REM) (dream) sleep which often followed the deep sleep during early stages of the nap. That is, the beneficial effect was proportional to the amount of nap time spent in both slow-wave sleep and REM sleep, not either alone. It may be that memories are reactivated by cuing during deep (slow-wave) sleep, but that the actual cell-level storage of memory is provided by REM sleep.

Implications of this approach to enhancing learning and memory show a great deal of promise. Can it be used for enhancing learning in school? Can it be used in rehabilitation of addicts or criminals? But there is a dark side. Now might be a good time to re-read Huxley's Brave New World wherein he actually described conditioning values in young children while they slept. Sleep is a state where people are mentally vulnerable and without conscious control over their thoughts. Malevolent people could impose this kind of conditioning and memory enhancement on others for nefarious purposes.  These techniques may have valid social engineering applications, but they must be guided by ethical considerations.

Dr. Klemm is author of Memory Power 101 (Skyhorse), Better Grades, Less Effort (Benecton), and Mental Biology (Prometheus).

Sources:

Klemm, W. R. (2013). New discoveries on optimizing femory formation.  http://thankyoubrain.blogspot.com/2013/05/new-discoveries-on-optimizing-memory.html

Hu, Xiaoqing et al. (2015. Unlearning implicit social biases during sleep. Science. 348(6238), 1013-1015.

Landmark Research: Why We Need to Get Enough Sleep

In other blog posts I have explained why sleep is good for the brain in general and memory formation in particular. Now a new discovery provides another reason for people to get enough sleep. The study examined a type of support cell in the brain, oligodendrocytes–let’s call them oligos for short. These cells wrap their membranes around nerve cells to form what is called myelin, which forms an electrical insulation in a way that speeds up the propagation of nerve impulses through neural networks. You may have heard about oligos in reading about multiple sclerosis, a disease that impairs nerve communication because oligos die and the myelin insulation degrades.

Speed of transmission is important–it influences IQ for example. As you know from buying a new computer, the faster processor speed gives it new capabilities your old clunker could not do. A similar idea applies to the brain.

Anyway, this new study, from the University of Wisconsin, focused on oligos because other research had shown that sleep promoted the expression of several genes that are involved in synthesis of cell membranes in general and those in oligos in particular. Unlike neurons, oligos die, and are replaced in the brain. Thus, anything that affects their turnover is important for brain function. Sleep has been implicated in this turnover because a common neurotransmitter in the brain, glutamate, is known to increase in wakefulness and decline during sleep. Glutamate  suppresses maturation of oligo precursor cells into formation of myelin insulation.

In this particular study, investigators examined a genome-wide profile of oligo gene expression in mice after a 6-7 hour periods of sleep or spontaneous wakefulness, or four hours of forced wakefulness (sleep deprivation). They found that 357 genes were expressed differently, depending on the time of day, in response to normal daily rhythms. More dramatic was the observation that 714 genes changed expression in conjunction with the sleep/wakefulness cycle, independent of the time of day. Of these genes, 310 were “sleep” genes that were selectively activated during sleep.

Many of the sleep genes contribute to maturation of oligos into myelin. In follow up experiments, mice were injected with a radiolabeled tag that marks the birth of new cells. Injection occurred eight hours before mice spent a long period of either of wakefulness or sleep. The number of newly born oligos was almost double in the sleep group compared to the wake group. More detailed analysis showed that this increase was specifically correlated with the amount of REM sleep (dream sleep in humans).

This REM effect may have particular importance in humans. Most REM sleep occurs in the early morning hours and only after substantial time has been spent in non-REM stages of sleep. Thus, cutting a night’s sleep short by getting up early may decrease the amount of REM time and thus the beneficial effects on oligo proliferation. So don’t feel guilty about “sleeping in” from time to time.

We might also think about how these findings could have special relevance to children, whose brains are incompletely myelinated. Getting children up early in the morning to start school at 8 AM may not be such a good idea. Until school districts get around to changing school hours, you might tell you kids about my learning and memory improvement e-book, Better Grades, Less Effort, available at Smashwords.com.

Source:

Bellesi, M., et al. (2013) Effects of sleep and wake on oligodendrocytes and their precursors. J. Neuroscience. 33 (36), 14288-14300.

New Discoveries on Optimizing Memory Formation

As each of us goes through life, we remember a little and forget a lot. The stockpile of what we remember contributes greatly to define us and our place in the world. Thus, it is important to remember and optimize the processes that make that possible.

People who compete in memory contests (“memory athletes”) have long known the value of associational cues (see my Memory Power 101 book). Neuroscientists have known for a long time about memory consolidation (converting short-term memory to long-term form) and the value of associational cues. But now, important new understanding is arising from a research lab at Northwestern that links cueing to “re-consolidation” and reveals new possibilities for optimizing long-term memory formation.

The underlying research approach is based on such well-established memory principles as:

1. When information is first acquired, it is tagged for its potential importance or value.
2. Such tagging is influenced by multiple factors such as repetition, attention, emotion, or purpose.
3. Valuable memories get preferentially rehearsed, either through conscious will or by covert (implicit) brain processes.
4. Rehearsal episodes reactive the memory and enhance long-term remembering because each re-consolidation episode builds on prior ones and strengthens the neural circuits that store the memory.
5. Effectiveness of recall during rehearsal is promoted by use of relevant cues, that is, information that was associated with the original learning material.
6. Such cues are effective, even when delivered during sleep.

The pioneering study involving sleep learning appears to have been done by John Rudoy and colleagues in 2009 [1}. They showed that people recalled locations of memorized objects better if they heard sounds associated with the locations during their sleep that had been earlier associated with the learning of object locations. The basic finding was replicated in a follow-up study [2].

Most recently, a study by another group also confirmed and extended this concept of using cues during sleep to promote memory formation.The study involved 60 people in their early 20s, screened for good memory ability.[3] All subjects participated in a four-hour learning period beginning in late morning. The learning consisted of 72 images placed in specific locations on a tile-like screen and presented one at a time. As each image appeared a corresponding sound was associated, intended to serve as a learning cue. For example, a dog picture would be associated with barking, cat with meow sound, etc. To create a value bias, each image had a superimposed number representing how important it was to remember this item and its location upon later testing. Subjects were given financial reward for how well they remembered, and thus remembering high-value images was a priority. Half of the images had high value assignments, while the rest had low values.

 Subjects were assigned to four groups:  

1. Groups 1 and 2 were tested to see how well they could remember where each object had appeared during the learning phase. They then took a 90 min nap while their EEGs were recorded. Half of these subjects heard white noise while the other have was presented the original sound cues of low-value images during non-REM sleep at a level that did not cause awakening. At the end of the nap, recall was again tested.
2. The procedure in two other groups was similar except that these subjects did not nap. One of these groups watched a movie during the 90 minutes after the learning session, while the other group listed to the low-value sound cues while performing a working memory task.

Not surprisingly, the studies revealed that high-value images were remembered better, irrespective of whether or not a nap was taken. The practical point is that we remember better the things we value and find to have positive reward value. This reminds me of the sage saying that T. Boone Pickens repeated from his basketball coach, who told players after each game: “Don’t dwell on your mistakes. Think about what you did right and do more of that!”

In the study, half of the low-value associations were rescued by cueing during wakefulness and all of them were rescued by cueing during sleep, even though only half of the images were cued. Notably, the best effects occurred during the deepest stage of sleep. No explanation was given to explain the sleep benefit, but I suspect it is because the sleeping brain is not distracting itself with irrelevant thoughts. This is consistent with the finding that low-value memories were not rescued well during REM sleep, when the brain is busily engaged in dreaming. The REM-sleep finding is at variance with other studies that reported a memory consolidating benefit of REM sleep. Apparently, the test conditions make a difference and more research is needed here.

Low-value associations were preferentially forgotten in the group that was not allowed to nap. This likely signifies that a brain busily engaged with other thoughts is less able to selectively consolidate memories, and only high-value items are likely to survive. This accords with the long-held theory that distractions and multi-tasking interfere with memory consolidation.

In summary, memory optimization would seem to require one to:

1.    Create associations that can serve as memory cues.

2.    Place a high value on the cues and their targets.

3.    Repeatedly present the cues and replay the initial information. When awake, present the cues in self-test mode. When asleep, even better results would obtain if cues were presented at a level that does not cause awakening during the early night sleep when sleep is deepest and there is little dreaming.

---

1. Rudoy, J. D., Voss, J. L., Westerberg, C. E., Paller, K. A. (2009). Strengthening individual memories by reactivating them during sleep. Science. 326: 1079.

2.. Antony, J. W, Gobel, E. W., O’Hare, J., K., Reber, P. J., and Paller, K. A. (2012). Cued memory reactivation during sleep influences skill learning. Nat. Neurosci. 15: 1114:1116.

2. Oudiette, D., Antony, J. W., Creery, J. D., and Paller, K. A. (2013) The role of memory reactivation during wakefulness and sleep in determining which memories endure. J. Neurosci. 33(15): 6672-6678.

Don't forget to check my memory e-book, Better Grades, Less Effort, 

for only $2.99 at Smashwords.com.

10 Ways to Slow Mental Decline with Age

Deterioration of the brain usually sneaks up on us. By the time we realize it, it may be too late. As we get older, we more frequently start asking questions like “Where did I put the car keys?” “What was it I was supposed to get at the store?” “What’s your name again?” Most of us have had to ask questions like this, and it seems to happen more often as we get older. We can’t turn back our biological clock, but there are things seniors can do to reduce the rate of their mental decline. The time to act is while you are still relatively young.

 I have made a career out of studying brain and behavioral research literature, and I know some of this research is relevant to everyday memory problems. I have summarized these findings in my new book, Memory Power 101 (298 pages, $14.95, Skyhorse.com), and keep readers up to date with my blog (thankyoubrain.blogspot.com).

As people age, beginning in early middle age, many of them experience a brain deterioration that progresses silently over the next decade or two, sometimes ending in devastating senility. Behaviorally, aging can cause your reflexes to slow. You walk and act slower. You even talk slower. Our memory starts to fail, especially the short-term form of memory ability that is so crucial for learning new things.

Now that bran-scan technology is widely available, physicians have discovered that the brain usually shrinks as people get older. The shrinkage increases the space between the brain surface and the skull. The cavities that hold cerebrospinal fluid get bigger. Nerve tracts in the brain shrivel, even leaving gaping holes in the brain. The “dendritic trees” shrivel, and these have major consequences because dendrites are the parts of neurons that form the contact points, and their loss reduces brain circuitry. You may also lose 40% or more of your dopamine neurons, and that may lead to Parkinson’s disease

For aging individuals, the challenge is to reduce the rate of their decline. This has created a growth anti-aging industry focused on vitamins and supplements, fad diets, gym facilities, mind training programs.  The good news is that some of these things work, if they are begun while people are in early middle age. Given that our country now has so many baby boomers in the over-50 category, it seems useful to summarize some things people can do to prevent or slow memory decline as they age. I particularly like the summary at this site.

Here is an expanded list of things I think are especially important for people entering middle age.

1. Get better organized. Many things we try to remember do not have to be remembered if we get better organized. Car keys, for example, should ONLY be in the car, your pocket/purse, or the same place in your house. Ditto for many other objects, such as purse, hat, glasses, etc. Life is a lot simpler when you have a place for everything, with everything in its place. Habit relieves the memory.

2. Make a special effort to pay attention, concentrate. Research shows that aging reduces a person’s ability to focus and pay attention. This also means that seniors have to work harder at filtering distractions, such as when we open the refrigerator door and forget what we are looking for because we thought of something else before we opened the door. New learning has to be consolidated to form lasting memory, and this takes a little uninterrupted time and conscious rehearsal right after you learn it. Seniors are especially susceptible to having temporary memories wiped out by distractions.

3. Challenge yourself mentally. Seek out new experiences, an active social life, and mental demands such as learning a new language, playing chess, or getting an advanced college degree. Learning new things always has the benefit of making you feel good about yourself, and this is especially true for seniors who accomplish things most people think they can’t do. By the way, there is abundant research literature showing that a lifetime of vigorous learning helps stave off Alzheimer’s disease.

4. Reduce Stress. Acute stress helps you be alert, pay attention better, and increase your chances of remembering what is happening at the time of stress. But chronic stress, whether caused by the same or different stressors, clearly disrupts memory formation and recall. Chronic stress and the hormones it releases can actually kill neurons and shrink the brain (which shrinks with age anyway, and only gets worse with chronic stress).

5. Eat foods with vitamins and anti-oxidants. Make certain you have a balanced diet. Supplements usually won’t help memory unless you have a nutritional deficiency. But even with a good died, adding vitamins C, D, and E can be helpful. Several research studies indicate a memory benefit from eating foods loaded with anti-oxidants. Blueberries (especially on an empty stomach). Another potent anti-oxidant is an ingredient in red wine, resveratrol, but there is no way you could drink enough; however, resveratrol supplements are now on the market. There is also suggestive evidence for memory improvement from omega-3 fatty acids and folic acid. Pharmaceuticals to improve memory are in the works, but you may have to wait quite a while before research shows which ones really work.

6. Don’t get obese, especially in middle age.

Confocal microscopy reveals that every added pound of fat adds approximately one mile of capillary tubing. Obviously, all these added vascular tubing puts a strain on the heart. A diet that produces new fat may well contribute to hardening of the arteries, which in turn compounds the added workload on the heart. People who are obese commonly have high blood pressure and other risk factors involving metabolism.

Obesity is a common cause of diabetes, which adds its own toll on blood vessels and the heart, as well as on nerve cells. No wonder then that obese people may develop mental deterioration. The problem may be worse in women. The more a woman weighs, the worse her memory. No, I am not a chauvinist pig. This claim comes from actual research —by a woman, no less. Diana Kerwin and her colleagues at Northwestern University studied 8,745 ages 65 to 79 and found that for every one-point increase in body mass index, the score on a 100 point memory test dropped by one point.

A likely cause of mental decline in most people is diminished blow flow in small vessels that are easily plugged by cholesterol and lipids or ruptured by high blood pressure. These “mini-strokes” are probably quite common as we age, and though they go undetected, they cause a cumulative damage which progressively affects our behavioral and mental capabilities. Brain cells are among the most metabolically active of all cells: they constantly fire electrical pulses and secrete relatively huge amounts of secretions (neurotransmitters). The brain consumes about 20% of all the body’s oxygen, even though it only ways about 3.5 pounds.

When brain cells do die or are damaged for any reason, healthy neurons are assaulted by inflammatory chemicals, like cytokines, that are released by the brain’s immune cell system. Fat deposits not only stress the heart, they also increase the amount of cytokines, which are hormones that can cause inflammation. Brain inflammation is also commonly caused by infections such as colds and flu and by diets deficient in anti-oxidants.

7. Exercise the body. Though exercise doesn’t do much to cause weight loss unless you are a marathon runner of tennis singles champion, it has many other benefits (improved circulation of blood to the brain, improved levels of HDL cholesterol) that can directly benefit memory and cognitive function. Vigorous aerobic exercise can improve your circulation and perhaps blood flow in the brain. But there also seem to be memory benefits from exercise that is independent of blood circulation. We don’t know why. Maybe relief of stress and improved mood are factors. We know that positive emotions help memory, but for unknown reasons.

8. Exercise the memory. The more you make an effort to memorize, the easier it seems to get. Practice the memorization tricks used by “memory athletes” that I describe in my book. I describe in my book specific image-based systems (“peg systems”) for performing astonishing memory feats, such as card counting, remembering long strings of numbers, and remembering the gist of what is on every page of a magazine or book.

9. Get plenty of sleep. Many studies show the brain is processing the day’s events while you sleep and consolidating them in memory. This kind of “off-line” rehearsal occurs just for the learning experiences on the day of sleep. Naps help too! How’s that for good news?

10. Believe in your brain’s ability to get better. Of course genes and luck have a lot to do with how well one ages mentally. But genes and luck seem to be more common in people who do the nine things mention above. Too many seniors buy into the popular myth that old dogs can’t learn new tricks. They resign themselves to defeatism. But the bottom line is that, unless you have Alzheimer’s disease, you can improve your mental sharpness. Getting older has enough frustrations. Don’t compound them by tolerating mental decline. Enjoy an improved brain. 

How Sleep Helps Memory

 There is no longer any doubt. Sleep does improve the gelling or consolidation of memory for recently encoded information. Research is now focusing on how this happens and what other factors interact with the sleep effect. At least two processes seem to be at work: 1) sleep protects new memories  from disruption by the interfering experiences that are inevitable during wakefulness, and 2) sleep consolidates memories according to their relative importance and the learner’s expectations for remembering.

A good illustration of reducing interference comes from a study of napping at the University of Lübeck in Germany. The researchers knew about the extensive evidence that in wakefulness, new situations and stimuli can readily prevent new memories from consolidating. This is even true when learned material is recalled, because at that point the memory has to be reconsolidated and is therefore again vulnerable. The authors assumed that similar interference with memory formation could occur even after a sleep interlude.

To test the idea, they asked 24 volunteers to memorize  the two-dimensional location of 15 pairs of cards with pictures of animals and everyday objects. During the study time, they were also exposed continuously to a slightly unpleasant odor, which was intended to be an associational cue.

Forty minutes later, the volunteers were asked to learn a second, slightly different set of card pairs. This second task was to act as an interfering disruptor of the initial learning. The difference is that after the first memorization session, half of the group stayed awake and the other half took a nap. For 20 minutes during the break after the first study session, the odor cue was presented with the intent of helping to reactivate the memory of the first session. The awake group got the odor cue for 20 minutes just before starting the second learning session, while the sleep group got the odor cue during the last 20 minutes of the nap (dreaming did not occur, because it normally requires more than 40 minutes of sleep to start appearing).

When both groups were tested for recall of the first set of cards, the sleep group remembered much better (85% correct versus 60% for the awake group). The explanation begins with the knowledge that when temporary memories (as for the first card set) are recalled, they are vulnerable to being destroyed by new mental activity (as with the second card set). In this study, memory was reactivated in both wakefulness and sleep by the odor cue. Yet, the memorization processes that apparently persisted during sleep made the original memories more resistant to disruption. By the time of the second interfering task some 40 minutes later, much of the initial learning had gelled during sleep, but less so during wakefulness.

These authors also performed brain imaging that showed that the nap group had mostly completed a shift in activity from the temporary processing area (in the hippocampus) to storage areas in the cortex. This was not true for the awake group. You might say that sleep  enabled the information to be “uploaded from RAM to the hard drive” better than in the constant awake condition. Of course this computer metaphor breaks down in other respects. Biological memory is dynamic, readily degraded over time or changed by new experience. Also, recall of biological memory launches a reconstructive process whereby the memory can be reinforced or drastically altered.

        The practical application, as I see it, is to take a short nap as soon as possible after trying to memorize something really important. For example, during a study session for a school exam, take a nap right away so that it has a better chance to consolidate than if you stayed awake and got exposed to many new interfering situations and stimuli.

       Two new studies shed some light on prioritization of memory formation during sleep. We all have had the experience of improved memory if we know others expect us to  remember. I guess such improvement occurs because we work harder at it, using more intensive rehearsal and perhaps using deliberate association strategies..But we now find out from a recent study that the sleep effect on improving memory formation benefits from the relevance of the learned information. Since sleep usually occurs significantly later than the learning and original encoding, this effect must arise from the consolidation  process during sleep.

      A recent study from this same German research lab has revealed that sleep helps memory formation the most if you know you will need the information later. That is, it seems that the brain prioritizes its consolidation operations during sleep to favor consolidation of information that is most important. The study tested 193 volunteers for recall of a variety of memory tasks. Some subjects were exposed to the learning material early in the day, when there would be no sleep involved. The others were exposed to the same material late, just before the night’s sleep. When subjects were told they would be tested later, they were more likely to remember if they had slept immediately after the learning. This was true for both procedural tasks (like finger-tapping sequences) or declarative tasks such as word matching or stating card-pair locations. Moreover, subjects who were told they would be tested later spent more total time in the deepest stage of Sleep (Stage IV) than did comparable subjects who were not told they would be tested later. Presumably, the brain is using Stage IV to accomplish this differential consolidation process.

      In a recent study from a French group, the study focus was on sleep’s apparent ability to prioritize memory formation based on prior instructions to remember or forget items in a learning task. In the learning task, volunteers were shown 100 French words, one at a time. Fifty of these had accompanying instruction “to be remembered” and the other 50 “to be forgotten,” presented in a pseudorandom sequence that prevented more than three words of the same type being presented consecutively. After the training session, subjects were divided into two groups, one which was sent home to continue their normal activities and to sleep on their usual schedule for the  next three nights. The other group was denied the first night’s sleep after training, where they stayed up all that night watching movies or playing games.  Otherwise, this group was treated the same. On the fourth day, both groups were tested for recall with presentation the 100 of the original words and 100 new ones to serve as distracters. The task was to identify which words were in the original list.

      Questionnaires revealed any strategies the subjects used in trying to remember “to be remembered” words and trying to ignore “to be forgotten” words. No subject intensively rehearsed the original items during the three-day interval, but of course casual rehearsal was going on. Generally, subjects made associations of “to be remembered” words with memories of personal events or with short stories or sentences. Mental images were much less used. Of course, no such rehearsals occurred with “to be forgotten” words.

      Upon testing, both groups had about the same degree of correct recall for “to be remembered” words. But the sleep-deprived groups remembered more of the words they were not supposed “to be forgotten.” Thus, it would seem that during sleep, the brain preserved its ability to remember words that were expected to be remembered and discriminated against remembering words that were unimportant. Recall that the instructions to remember or forget were given at the  time of initial encoding. Thus, the brain must have preserved these instructions and followed them in the consolidation process during sleep. Though the authors did not mention it, the poor ability of sleep-deprived subjects to discriminate between the two categories of words could have arisen because being awake for a whole day after learning interfered with remembering and following instructions at the time of encoding.

Don’t forget, if you have students in your life, have them check out my new eBook, “Better Grades, Less Effort.”

Sources:

Diekelmann, S., Büchel, Born, J., and Rasch, Björn. 2011. Labile or stable: opposing consequences for memory when reactivated during wakefulness and sleep. Nature Neuroscience. Jan. 23. doi: 10.1038/nn.2744

Rauchs, G. et al. 2011. Sleep contributes to the strengthening of some memories over others, depending on hippocampal activity at learning. J. Neuroscience.  31 (7): 2563-2568.

Wilhelm, I. et al. 2011. Sleep selectively enhances memory expected to be of future relevance. J. Neuroscience. 31 (5): 1563-1569.

Neuroscience research working for you

I just attended the 40th annual meeting of the Society for Neuroscience in San Diego. There were over 31,000 scientists there, about 20,000 of whom presented research findings.Attendees come from all over the world. I an a Charter member of the Society and attended the first and most of the other annual meetings. It is hard for "outsiders" to appreciate just how much has changed in brain research over that time. The first meeting had less than 1,000 attendees. Now the meeting is so big that only a handful of U.S. cities can host such a large meeting.

There were many papers on memory presented. Most, however, were focused on how the brain achieves memory, and a lot of that has no immediate practical application for everyday life. I keep an eye out for such papers and report them in this blog when I find it.

One paper confirmed what I already knew about teaching "old dogs new tricks."  It showed that learning of a series of items was impaired in Seniors compared to younger people, but the deficiency was overcome if the experimenters just increased the interval between presentation of items. In other words, you CAN teach old dogs new tricks, it just takes longer.

I was really excited to see that I am on the right track on my new book, due out from Springer next Spring. The book is titled "Atoms of Mind. The 'Ghost in the Machine' Materializes." A few scientists are starting to do  the kind of research I advocate in the book for the study of consciousness. While at the meeting, I got a new idea nobody has considered yet. I'll tell people about it in the book, which I am mailing off to the publisher in a week or so..

I presented a paper on why people dream. A commonly accepted idea is that we dream to consolidate memories of the preceding day's events  It is true that memory consolidation does occur in sleep, both dream and non-dream sleep. But that is not the CAUSE of either dreaming or non-dreaming sleep. It is the consequence.

The simple answer is that we dream because the brain becomes activated in what is called REM sleep. Activated brains want to think, and thinking during sleep is expressed as dreams. So the real question I addressed is why do we have REM sleep. It's a long story, but the short answer is that REM helps to re-boot a sleeping brain so that we can become awake and conscious again. My presentation was well received. I had 50 copies of handouts, and they were scarfed up in the first 30 minutes of my poster session. Lots of people left their e-mail address so I could mail them copies of the poster. Over 100 people came by the poster. And they weren't window shopping. They stayed, read it all, and discussed it with me during the time when I was attending the poster. Nobody could punch any holes in the theory. I think I have the best explanation anybody has every presented.

It has been a stimulating four days. I will need some time to unwind.

More Evidence that Naps Help Memory

I have mentioned before the value of naps for improving the formation of memories. Another recent student confirms this conclusion. Matthew Walker and colleagues an the University of California at Berkeley divided 39 young adults into two groups. At noon, all the participants took part in a memory exercise that required them to remember faces and link them with names. Then the researchers took part in another memory exercise at 6 p.m., after 20 had napped for 100 minutes during the break.

Those who remained awake performed about 10 percent worse on the tests than those who napped, Walker said. Students take note: 10% can be the difference between an A and a B.

Source: Walker, Mathew. 2010. Current Models of Mechanisms of Sleep-Dependent Memory Presentation at the annual meeting of the American Association for the Advancement of Science meeting, San Diego, Feb. 21.

Sleep Learning -- A New Perspective

A couple of decades ago, many people thought you could learn while you sleep. I remember as a college student playing audio tapes of information I wanted to learn while I slept. This idea turned out to be a fraud, perpetrated by people who sold sleep learning materials and equipment. Most "early adopters" found that all it did was disrupt sleep.

But as I have discussed elsewhere, modern research has compellingly shown that the brain is consolidating memories of the day's events during sleep. So, maybe the sleep learning idea is not completely dead. Maybe the right kind of stimulus input while you sleep could promote learning, at least in terms of promoting memory consolidation of the information you already learned during the day.

So, the idea would be to see if sleep can promote memory consolidation of things you recently learned, but have not yet formed into lasting memory. How might you do that? Since memory is largely associative, maybe it would work to provide during sleep the cues that were associated with the original learning. This might have a better chance of working during the dream stage of sleep, because it is well documented that external sound stimuli (like storms, rain, etc.) are documented as capable of becoming incorporated into and changing the course of a dream. Thus, the question becomes: can audio presentation of learned association cues during dreaming promote the memory formation for the original learning items or events. The idea is that the cue might reactivate a latent memory and thus constitute a memory rehearsal.

Partial testing of this idea has recently been reported. Northwestern University scientists trained human subjects to recognize the location of 50 different objects on a computer screen. Each object had an associated sound. For example, the cat image was associated with a meow sound, a kettle with a whistle, etc. Then people took a nap, during which sound cues were presented (unobstrusively at 62 decibels) for half of the images they had previously been exposed to. After the nap, subjects had no conscious recollection of the sound cueing.

The cues were presented oddly enough only during the deep stages of sleep, not during dreaming. Maybe the researchers were unaware that external stimuli can get incorporated into dreams. Even so, the original objects were re-presented after waking and subjects tested for recall of the location of the 50 images.

Measuring the location errors in terms of distance from correct position indicated that accuracy was greater for images that had associative cues presented during the nap than for those images for which cues were not re-presented. Simultaneous recording of brain waves (EEG) showed that the brain was responding to the sensory cues during sleep.

Tests in control subjects, who were tested without the intervening nap, showed that the cues provided no improvement in recall.

The principle seems sound. What remains is for clever entrepreneurs to develop memory-enhancing strategies that are specific for specific learning tasks.

The old ideas of sleep learning are dead, but here is a new opportunity for finding ways to get sleep to work for us. Learning protocols have to be developed for specific learning tasks, and these have to have relevant sound cues. Finally, I suspect that such external learning "reminders" will be more effective when presented during dream sleep, not the deep stage of sleep in which people "fall into a pit" of oblivion. The challenge is to find ways to provide appropriate reminders while we sleep (or dream).

Source: Rudoy, J. D. et al. 2009. Strengthening individual memories by reactivating them during sleep. Science. 326: 1079.

Remembering the Bad Along With the Good

In my Sept. 15, blog I surveyed an experiment that showed people learning more from their successes than from their failures. In so doing, I raised the possibility that the learning gain was promoted by the release of the "reward transmitter," dopamine. Now I find a new research report on the effect of dopamine on the long-term storage of bad memories. The process studied was the long-term memory of fear and pain. Rats were trained to remember a strong foot shock, which lasted at least 14 days. Injecting a dopamine blocker into the hippocampus erased the long-term memory if given 12 hours after the original foot-shock experience. This suggests that the normal release of dopamine can promote memory, which is not surprising since dopamine promotes the formation of proteins used in synaptic junctions of neurons.

However, foot shock is certainly not rewarding and probably does not release dopamine. But the end of the foot shock pain is a rewarding relief. Also, rewarding things do happen even to rats after a nasty foot shock (like sex with mates, eating, drinking, sleeping, etc.). The ongoing release of dopamine in the course of just living may help rats form lasting memories, regardless of the nature of memory. This raises questions that scientists have not studied yet. But it may be that dopamine helps us remember both the good and the bad. And maybe is one reason why bad memories are hard to erase.

Source: Rossato, J. et al. 2009. Dopamine controls persistence of long-term memory storage. Science. 325: 1017-1020.

Caffeine or Nap: Which Helps Memory?

Caffeine gets our brain pumped up. We are more alert and perhaps should remember things better. Naps have recently been found to help the memory consolidation process. Until now, nobody has made a direct comparison of these two factors in the same people under identical conditions. But Sara Mednick and her colleagues at the University of California, San Diego, now report some helpful findings.
They tested caffeine in a single dose of 200 mg (roughly equivalent to 2-3 cups of coffee) and compared with an episode of napping (60-90 min) or placebo on the effects on performance on three types of memory tasks. For verbal memory, they tested recall and recognition memory of word lists 7 hours after learning, with an intervening nap, caffeine dose, or placebo. In addition, they conducted memory tests for a finger tap and texture discrimination task.They also conducted short-term memory on a different set of words after the first experiment.
Compared with either caffeine or placebo, naps were more effective in the word recall test, both in the consolidation test and in the short-term memory condition. Caffeine actually impaired word recall in the short-term memory task, even though the caffeine had been given some seven hours earlier. Naps also improved recognition memory in the consolidation test and recall of the texture discrimination learning. For the finger-tap learning, naps were ineffective and caffeine markedly impaired performance. The caffeine group did feel less sleepy in the late afternoon immediately prior to the memory testing, but that did not help their memory performance.
What I take from this is that the morning coffee may help you awaken, but don’t count on it to improve your memory. Other research does show that caffeine enhances mood and alertness, reaction times and speed, but don’t count on it to help your memory for things you learn that day. Note to students: all-night study sessions are a bad idea for lots of reasons and probably made much worse by drinking lots of coffee. Note to bosses: letting workers take an afternoon snooze might be a good idea.

Source:
Mednick, S. C. et al. 2008. Comparing the benefits of caffeine, naps, and placebo on verb al, motor and perceptual memory. Behavioural Brain Research. 193: 79-86.

Overtraining: You Can Learn Too Much

Naps may be helpful for learning tasks other than those involving movement (see earlier note on work by Korman et al.).* An early study on the effects of napping had developed a useful texture discrimination task in which a visual display of horizontal bars has superimposed on it a brief display of three diagonal bars, followed by a blank screen, and then by a mask. The interval between the target and the mask is varied and the interval needed to achieve 80% correct responses is used as a measure of perceptual ability and working memory.

After a single training session, performance on this task improves only after subjects have had a normal night's sleep after the day's training. To be effective, a normal amount of dream sleep, which occurs mostly in early morning, is needed.

In a follow up study by another investigator, subject performance unexpectedly deteriorated if they were given 60-minute training sessions four times at regular intervals on the same day. In other words, the more the subjects were trained, the poorer they performed. However, this interference did not occur if subjects were allowed to nap for 30-60 minutes between the second and third sessions.

It is hard to explain why over-training disrupts performance, but one has to suspect that as training trials are repeated the information starts to interfere with memory consolidation, perhaps because of boredom or fatigue in the neural circuits that mediate the learning. Napping must have a restorative function that compensates for the negative effects of overtraining. What all this suggests to me is that memory consolidation would be optimized if learning occurred in short sessions that are repeated but only with intervening naps and on different days with regular night-time sleep. In other words, repeating long study periods in the same day on the same task can be counter-productive. This is yet another reason why students should not cram-study for exams. Learning should be optimized by rehearsing the same learning material on separate days where normal sleep occurred each night.

See my book on what science reveals about improving everyday memory. I also give seminars and workshops.

Sources:

Maquet, P. et al. 2002. Be caught napping: you're doing more than resting your eyes.Nature Neuroscience. 5 (7); 618-619.

Mednick, Sara, et al. 2002. The restorative effect of naps on perceptual deterioration.Nature Neuroscience. 5 (7): 677-681.

Need to Learn Something Quickly? Try a Nap

Daytime naps are said to rejuvenate energy and lower stress. Now there is evidence that naps speed up consolidation of memories. Maria Korman and her group at the University of Haifa evaluated consolidation of a procedural memory task of learning to bring the thumb and finger together in a specific sequence. Half of the subjects were allowed to take an afternoon 90-min nap after training, while the other group stayed awake. The group that napped showed a distinct improvement in task performance when tested that evening. After a night's sleep, both groups showed the same improvement in acquired skill. So, it would appear that the nap just speeded up the consolidation process, rather than improving on the improvement that a regular night's sleep can produce.

The role of napping on interference effects was also tested. We know from numerous studies that consolidation of new learning is easily disrupted by distracting or other new learning experiences. In this experiment, another group of subjects learned a different thumb-to-finger movement sequence two hours after practicing the first task. Learning a second task right after the first was expected to interfere with learning of the first task. This proved to be the case; there was no improvement in performance of the first task either that evening or the next day after a normal night's sleep. However, based on the findings of the first experiment where a nap speeded up consolidation, the experimenters created yet another group of subjects that were allowed a 90-min nap between learning the first movement task and the second movement task. In this case, performance on the first task was improved when they were tested the next day after a normal night's sleep. Thus, the nap actually prevented the otherwise memory disrupting effect of a second learning task, presumably because the nap speeded up memory consolidation of the initial learning so that it was resistant to interference effects.

There are practical implications here, at least for procedural memories. This study indicates that if you need to learn a "how to" kind of task quickly, you should take a nap just afterward. One perhaps trivial illustration might be for football coaches who introduce some new training in the morning of a game to be played later that evening. After the morning workout, they should let the players take a nap that afternoon. Or for "two-a-days" workouts in the summer, maybe players need a nap between sessions, not just to rest but to consolidate the training.

Source: Korman, M. et al. 2007. Daytime sleep condenses the time course of motor memory consolidation. Nature Neuroscience. 10 (9): 1206-1213.