by Gary L Wenk
What is a lucid dream?
For the majority of people, dreams are typically not volitional, that is, not under their direct control, nor do they feature self-reflection, insight, judgment, or abstract thought. Some people, however, are able to control the content of their dreams—we call these people lucid dreamers. How do the brains of lucid dreamers differ from the brains of nonlucid dreamers? When nonlucid dreamers are dreaming, the frontal lobes of their brains remain relatively inactive. In contrast, when lucid dreamers are dreaming, the dorsal, or top, part of the frontal lobes of their brains are quite active. Neuroscientists believe that this difference in the activation pattern of the frontal lobes underlies the ability of lucid dreamers to be self-aware during their dreams and to be able to adjust their dream narrative. Lucid dreaming is much more common among children and adolescents than among adults. This suggests that the loss of the ability to experience lucid dreaming is related to maturation of the brain.
The ability of some people to recall their dreams better than other people also may be related to which brain regions are active while they are dreaming. People who recall their dreams better have more blood flow within their medial frontal and posterior temporal lobes while dreaming than do people who do not recall their dreams as well. Thus, remembering dreams depends upon whether or not the appropriate brain region was paying attention (i.e., was active) while you were dreaming.
How long do dreams last?
While you are dreaming your brain does have the ability to estimate the passage of time without referring to time cues. The accuracy of this function fluctuates, however, from an overestimation during the initial hours of sleep to an underestimation during the final hours of sleep just before waking. Why? Time flows faster during non-REM sleep, which predominates during the initial phases of sleep. Thus, dreams during non-REM sleep are associated with longer estimates of sleep time subjectively experienced. In contrast, REM sleep predominates during the early morning hours. Thus, REM sleep is associated with longer estimates of sleep time subjectively experienced. Therefore, during the few hours just before your alarm sounds in the morning, your dreams seem to take a lot longer to unfold.
Does it matter what time I get up or go to bed?
Yes. Morning types get up early, perform mentally and physically best in the morning hours, and go to bed early. Evening types prefer to stay out late, get up at a later time, and perform best, both mentally and physically, in the late afternoon or evening. Evening-type individuals were significantly more likely to suffer from poor sleep quality, daytime dysfunction, and sleep-related anxiety as compared with morning-type individuals. Even more disconcerting is that late bedtime is associated with decreased hippocampal volume in young healthy subjects. Shrinkage of the hippocampus has been associated with impaired learning and memory abilities. So yes, it probably does matter what time you prefer to get up and go to bed.
Does it matter who I sleep with?
Yes, very much. Couples sleeping in pairs were investigated for sleep quality, that is, for the correct balance of non-REM and REM, as well as their own subjective view of how they slept. For women, sharing a bed with a man had a negative effect on sleep quality. However, having sex prior to sleeping mitigated the women’s negative subjective report, without changing the objective results; that is, her balance of non-REM and REM was still abnormal. In contrast, the sleep efficiency of the men was not reduced by the presence of a female partner, regardless of whether they had sexual contact. In contrast to the women, the men’s subjective assessments of sleep quality were lower when sleeping alone. Thus, men benefit by sleeping with women; women do not benefit from sleeping with men, unless sexual contact precedes sleep—and then their sleep still suffers for doing so.
Why do I need that morning cup of coffee?
The alarm rings, you awaken, and you are still drowsy: why? Being sleepy in the morning does not make any sense; after all, you have just been asleep for the past eight hours. Shouldn’t you wake up refreshed, aroused, and attentive? No, and this is why. During the previous few hours before waking in the morning, you have spent most of your time in REM sleep, dreaming. Your brain was very active during dreaming and quickly consumed large quantities of the energy molecule ATP. The “A” in ATP stands for adenosine. The production and release of adenosine in your brain is linked to metabolic activity while you are sleeping. There is a direct correlation between increasing levels of adenosine in your brain and increasing levels of drowsiness. Why? Adenosine is a neurotransmitter that inhibits the activity of neurons responsible for making you aroused and attentive. You wake up drowsy because of the adenosine debris that collected within your brain while you were dreaming. The cure for your morning drowsiness: coffee. The caffeine in your coffee blocks the actions of adenosine and releases your neurons from their chemical shackles; your attentiveness improves and you are ready for anything—at least until the effect of caffeine wears off.
Caffeine is the single most widely consumed (legal) psychoactive ingredient in the United States. It is easy to understand why. It quickly enhances our physical and cognitive performance and usually improves our mood. Numerous studies have shown that caffeine improves performance on attentional tasks. Unfortunately, most of these studies were performed on young adults; neuroscientists know very little about the potential benefits of coffee in older adults. Some studies have found no benefits while others have concluded that older adults actually benefit more from caffeine than do younger adults.
Can I get too much sleep?
Do you remember when you were a child and had the measles, or some other infection, and you fell asleep on Monday and woke up on Thursday? When you are sick, elevated levels of invading bacteria or viruses induce your immune system to defend you. The debris from this battle includes a collection of molecules released from the carcasses of these invading bugs, including pieces of bacterial cell wall (called lipopolysaccharide) and bits of nucleic acids from inside the viruses. This is all part of your normal immune response. As a consequence, these inflammatory proteins floated into your brain and induced a normal and very prolonged sleep cycle. Your brain evolved to respond to illness by making you sleep in order to allow your injured or infected body to heal.
This same principle is true for other animals. Animal species that sleep more tend to be healthier. The daily number of hours an animal sleeps is correlated with the total white blood cell count and inversely correlated to the relative frequency of infections experienced by that animal species. Sometimes, however, the normal response of the brain to induce sleep goes too far and sleep can last too long.
Kleine-Levin syndrome is a good example of this extreme response by the body. Occasionally, following a minor flu-like illness with upper airway infection and an acute mild fever or even tonsillitis, some people will experience attacks of excessive sleeping, called hypersomnolence, which usually appear and end quite suddenly. Sometimes sleep lasts from several days to several weeks. The interval between attacks can last for several weeks to months, and sometimes even many years. Thus, getting too much sleep is not always an indication of good health.
What if I do not get enough sleep?
Although scientists have not discovered why we sleep, they have discovered that we need between six and eight hours every night. Not getting enough sleep makes us more likely to pick fights and focus on negative memories and feelings. The emotional volatility is possibly due to the impaired ability of the frontal lobes to maintain control over our emotional limbic system. We also become less able to follow conversations and more likely to lose focus during those conversations. Sleep deprivation impairs memory storage and also makes it more likely that we will “remember” events that did not actually occur. Extreme sleep deprivation also may lead to impaired decision-making and possibly to visual hallucinations. Not getting enough sleep on a consistent basis places you at risk of developing autoimmune disorders, cancer, metabolic syndrome, and depression. Why? Some recent studies have reported that
sleep is important for purging the brain of abnormal, and possibly toxic, proteins that can accumulate and increase the probability of developing dementia in old age. Whatever you are doing right now, stop and go take a nap. When you get older, you will be glad that you did.
What happens to sleep with aging?
Normal sleep becomes quite disturbed with normal aging. First of all, it takes you a lot longer just to fall asleep; in addition, you are going to experience more nighttime awakenings. This leads to a greater tendency for daytime sleepiness and the need for short naps. Part of the problem is that older humans enter the deeper stages of sleep less often. This causes some health problems because it is during the first deep sleep periods that your body releases hormones necessary for healing and growth. The consistent loss of these deeper stages of sleep may contribute to slower wound healing and increased vulnerability to diseases that often fall into the category of age-related disorders. The aged brain also spends less time in REM sleep. The consequences of reduced REM sleep likely underlie age-associated problems with learning and memory.
Insomnia and other sleep disturbances are common in patients with neurodegenerative disorders, such as Alzheimer’s disease and other dementing disorders. Disturbed sleep patterns, including chronic insomnia, represent a significant public health concern that is relatively common across all cultures.
Insomnia is possibly the first sign of aging in humans. Sleep problems that are similar to those seen in the elderly first appear just after puberty. Most people experience their deepest, restive sleep around the age of 10; then, sleep quality begins to decline. Sleep problems are associated with a poorer quality of life, as well as with mental and physical health problems. Does physical activity help us sleep better? An analysis of over 50 recent studies found that regular exercise, regardless of exercise intensity or aerobic classification, had a rather moderate benefit on overall sleep quality, and only a small positive benefit on total sleep time and sleep efficiency. So, if a little exercise only offers a modest benefit for sleep, what else might help? Low doses of melatonin also may be an effective option for the treatment of insomnia. Sadly, typical over-the-counter sleep aids are only modestly effective, quite addictive, and ultimately lose their effectiveness within a few days. In addition, all of the over-the-counter sleep medications are common antihistamines that do not reproduce normal sleep patterns. That is why your sleep is not restful when using these medications. It is usually best to avoid these medications, particularly as you get older.
5
HOW DOES THE BRAIN AGE?
This is an essential question to answer because the brain is a key regulator of your lifespan. Your body ages almost as fast as your brain; thus, anything that you do to slow the aging of your body will be reflected in a slower aging of your brain. Many of the brain’s functions discussed in previous chapters, such as sleeping, learning and memory, eating behaviors, and emotional stability, may change significantly during normal and pathological aging. The nature and severity of these changes depend upon numerous factors, including diet and drug use, sleeping habits, and inherited vulnerabilities. During the past decade, it has become clear that the body’s normal repair processes are programmed by your DNA to decline or are forced to decline due to your lifestyle choices.
How fast you age is almost entirely related to how your body generates the energy that your brain requires to function. Is there any way to slow this process down? Yes, there is; the best advice anyone could possibly provide was offered over 2,400 years ago by Hippocrates of Kos:
If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.
Alternatively: All things, including food and exercise, in moderation. Apparently, humans were overindulging even two millennia ago.
When does age-related senescence begin?
This is not an easy question to answer. Aging is hard to define; scientists usually define it operationally depending upon what feature of aging they are studying. People age at vastly different rates for quite different reasons: it all depends upon one’s lifestyle. Did you smoke? Were you obese? These two factors are responsible for most of human aging and poor health. In addition, one’s age according to the calendar does not necessarily correlate with a decline in all cognitive abilities. For example, as you age, your vocabulary will continue to improve and you might cultivate some subtle social skills. The earliest true sign of aging is a decline in sleep quality and the consequent impaired learning, memory, and attentional abilities during the day. As mentioned in Chapter 4, the release of adenosine in your brain is linked to metabolic activity while you are sleeping. Older brains have more difficulty rinsing out extracellular adenosine, thus leading to impaired learning and attention.
The second age-defining change is heralded by a reduction in your ability to experience strong emotions. Overall, with normal aging, the brain makes numerous compensatory changes in how information is processed in order to allow mental activity to remain somewhat normal. This chapter will begin by examining what happens during brain aging and then conclude with a discussion of what has been proven scientifically to slow brain aging. First, let us skip to the end of the story.
When am I going to die?
Many factors determine brain aging and, therefore, influence when you will die. Some of these factors have good explanations; others do not. The month in which you were born is related to how long you live. In the northern hemisphere, people born in May or December live longer than people born in February or August. You are far more likely to die in the months of January or February than in July or August. These statistics are biased due to the fact that most of the world’s population lives in the northern hemisphere of the planet; thus, most of us experience cold winter nights in January and February.
Most people who die in their sleep usually die during the early morning hours when their body temperature is lowest, and it is easiest to become colder at night in the winter months. Do we really get so cold at night that we are at risk of dying? Yes. How is this possible, given that we have no problem staying warm during the day? The problem is that during REM sleep, the time that you are busy dreaming, your highly evolved mammalian brain does something truly bizarre: it reverts you back to the physiology of a lizard and you become a poikilotherm. Poikilotherms are animals, such as fish, amphibians, and reptiles, whose internal temperature varies in parallel to the ambient temperature of their environment. Therefore, because you spend so much time in REM sleep during the early morning hours, your body temperature is not defended by your brain and you slowly cool down. This is why in the morning you wake up feeling cold: you are cold.
Consequently, due to the fact that your body temperature is falling throughout the early morning hours, considerable stress is placed upon an aging cardiovascular system. Hence, elderly humans with failing cardiovascular function, an all too common condition today, tend to die during the early morning hours; you can chalk this up to your evolutionary link to reptiles. As you will read later, however, sometimes being just a little colder has significant advantages.
How can I live longer?
Some people live very long lives. What did they do differently from their contemporaries who died before them? Scientists have discovered some of their secrets by interviewing centenarians. Humans who have lived to be more than 100 years old consistently report three important lifestyle features: they lived most of their lives in the same place and near family members, they did not use tobacco products, and they used as few medicines as possible. In addition, being from a higher economic status, obtaining a higher education that leads to a nonroutine profession, being female, and having long-lived parents all correlate with a longer life.
Females of all species, whether flies, beetles, rats, spiders, or humans, live longer than males. Why? There may be a relation between telomere length and age. Telomeres are critical pieces of our DNA; every time a cell divides, the lengt
h of the telomere shortens. Women exhibit less telomere shortening over time than do men. Recent evidence suggests that this accounts for the longer lifespan of women. In addition, the presence of testosterone in men makes them age faster. To understand why men always die sooner than women, you also must understand the effects of eating.
How does eating age me?
Like most other animals on this planet, humans acquire energy for our biochemical machinery by breaking down the carbon bonds found in fats, sugars, and proteins, and then gobbling as much energy from the process as possible. Recent studies have discovered that humans, probably due to our massively active brains, metabolize food much faster than other animals. Much of the energy in our food is lost to heat that helps to maintain our body temperature. The process of extracting energy from the fats, proteins, and carbohydrates in our diets leaves our cells with leftover carbon atom debris. Think of this carbon debris as similar to the ash left over after a fire has consumed a piece of wood. This carbon atom waste must be discarded somehow. The solution for your cells, a solution that evolved at least 3.5 billion years ago, is to combine these leftover carbon atoms with oxygen. Your cells simply expelled this waste product as a gas called carbon dioxide: one carbon and two oxygen atoms bound together. Voilà, the problem was solved: carbon bond energy is consumed in the form of fats, carbohydrates, and proteins. Our bodies then extract energy and excrete the residue as carbon dioxide and water vapor. There was a big problem, however, with this ancient solution: oxygen is exceedingly toxic to our cells. Oxygen must be transported inside your body very carefully because oxygen causes oxidation; you might know this effect as rusting. Your body’s solution for handling such a toxic molecule is to bind oxygen to a protein in the blood called hemoglobin.