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

Naps and learning competencies

I have written before about research that clearly demonstrates improved learning after sleep. Sleep promotes the "consolidation" of recently acquired short-term memories into more permanent memories.  Impaired consolidation is a major problem in teaching and learning. Teachers often have to repeat the same instruction again and again, and yet many children still do not perform well on high-stakes tests. Anything teachers can do to improve retention of instruction would be useful, and that includes making school children aware that they probably need to get more sleep. The well-known change in sleep cycles during adolescence makes a strong case for starting school later in the morning. But another issue is whether or not naps during the school day would improve learning.

A recent study in Brazilian schools has addressed this question by having 371 6th graders take a nap after receiving a 15-minute lecture on intentionally novel information that was not relevant to the normal curriculum. Students were then given a surprise multiple-choice test on this content at three different times after the lecture: 1, 2, and 5 days after the lecture.  Scores were compared with that of a pre-test on this material before the lecture.

Students were divided into a nap group, in which students were given sleep masks and encouraged to try to sleep, lying down on mats in a quiet room. The other group went to a regular class by their usual teacher after the lecture.

Not surprisingly, both groups showed improved scores (12% gain) when tested the next day. However, this gain disappeared by five days in the non-nap group, whereas essentially no decline in test scores was evident at testing two or five days later. Teachers would not be surprised that students soon forgot what they are taught. In this situation, the preserved memory in the nap group was especially impressive, given that the study was designed to impair learning in both nap and non-nap groups in four ways:

1.      Students were not allowed to take notes.

2.      Students were not encouraged to remember this information.

3.      The lecture topic was not relevant to the curriculum.

4.      Students did not know they were going to be tested.

If these constraints on learning had not been present, I suspect that the nap effect would have been much larger. Moreover, there was no objective measure of how much actual sleep each student had. Many might have just been resting. Data were not tracked by individual student, but rather averaged over the whole group. Finally, multiple-choice tests were used, and these only test recognition memory. If naps do improve memory, a larger nap effect might be seen with tests that call for students to generate a remembered answer, as in short answer or fill-in-the blanks tests.

While theory and experiments such as this suggest that napping could help student learning, there are of course practical constraints. Time spent napping is time that content cannot be presented.

My experience as an educational consultant in schools is that schools seem to conspire to make learning difficult. First, students are constantly over-stimulated and distracted, not only by social interactions, but by posters, pictures, and do-dads placed conspicuously all over the rooms and in the halls. Many teachers allow students to multi-task, for example, using cell and smart phones in class. Classes are commonly disturbed by loud public-speaker announcements from the principal's office and by loud bells signaling the end of class. Immediately after class, no quiet time is allowed for reflection on what happened in class. Students actually start tuning out about five minutes before the anticipated bell ring, and the bell causes them to leap up, run out into the halls, and start socializing. Then, of course, there is the emphasis on all manner of extracurricular activities that occupy the minds of many students much more than curriculum. It's a wonder students learn anything.

Finally, few if any teachers teach students how to learn. The emphasis is on what to learn and on performing well on state-mandated test scores. I have started to give teacher workshops to help teachers realize the importance of developing learning competence in their students. If students had better learning skills, the job of teaching would be much easier and student test performance would improve automatically.

Source:

Lemos, N. et al. (2014). Naps in school can enhance the duration of declarative memories learned by adolescents. Frontiers in Systems Neuroscience. Vol. 8, article 103. Doi: 10.3389/fnsys.2014.00103

Dr. Klemm is author of two books on learning and memory, Memory Power 101 and Better Grades, Less Effort.

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.

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.

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.