The Future of Sleep
The future of sleep research holds great promise. We will most likely see some truly significant discoveries in the genomics and molecular biology of sleep in the near future.
These discoveries will help us resolve questions about the function and evolution of sleep. Knowing the cellular/molecular processes that are involved in sleep will definitely give us clues as to function. And once we identify a cellular function of sleep in one species, we can then determine whether that same function occurs in species that do not share EEG features with mammals. In other words, we will be able to see the homologies between sleep in mammals and rest in other species, despite differences in brain structure and EEG patterns.
The Goal: Understanding Sleep
Expanded, improved, and universal education about sleep is critical to our future.
There are three essential components of a healthy life: nutrition, fitness, and sleep. Good nutrition is an emphasis in education from elementary school on. Classes in nutrition are common in colleges and universities. Shoppers are faced with mandatory nutrition labels on every prepared food they buy in the grocery store. The same is true for education in fitness. In addition to sports in high school and college, there is a multibillion-dollar fitness industry aimed at keeping us in shape.
When it comes to sleep, however, the dearth of public attention and education is appalling. Aside from mandatory naptime in kindergarten, elementary school students learn nothing about sleep. In high school, attitudes about sleep are tainted by the experiences resulting from the sleep phase delay that occurs with adolescents. The general public knows next to nothing about sleep, other than the fact that they can’t sleep. Industry usually handles shift work in the worst possible way.
￼• Too often the level of knowledge about sleep is not much better in the medical community. Many physicians simply conclude from an insomnia complaint that the patient is depressed. For most individuals, sleepiness is simply an inconvenience, and quality sleep is elusive. Knowledge about sleep, good sleep habits, and the value of good sleep is essential.
Monitoring Your Own Sleep
Monitoring one’s own sleep health is now possible. Just as you can buy devices to monitor your blood pressure, your blood oxygenation, and
your blood glucose,
you can now buy devices to monitor your sleep. A wrist actigraph, which records movement throughout the day and night, is fairly reliable in revealing total sleep time and sleep efficiency.
also are analyzing
There is even new
enables you to record and analyze your own EEG. The electrodes, incorporated into a headband, communicate wirelessly to a recording device that sits by the bed. Associated software interprets the data for you.
The Consequences of Sleep Loss
A critical issue in sleep research is the long-term consequence of sleep loss or poor sleep. One laboratory that has made
￼Knowledge about sleep, good sleep habits, and the value of good sleep is scarce, but paying attention to sleep is an important step on the path to good health.
○ Some years back, Dinges developed a simple method for
measuring alertness that has become a standard technique in the field of human sleep research. It is called the psychomotor vigilance test (PVT).
○ The basic form of this test is that the subject hears a tone or sees a light flash on a screen and has to respond by pushing a button. The individual must pay close attention to the task. The computer registers several metrics of performance: time to respond, failure to respond, and false responses. Typically, after some sleep manipulation, subjects perform the PVT during the subsequent day.
In an experiment, groups of subjects were restricted to 4, 6, or 8 hours of time in bed per night for 2 weeks.
○ After 6 nights of restricted sleep, the 4-hour group had an
error rate equivalent to what was seen after 1 day of total sleep deprivation.
○ After 12 nights, the error rate of the 4-hour group was the same as what was seen after 2 days of total sleep deprivation.
○ After 11 nights, the group receiving 6 hours of sleep each night had an error rate equivalent to what was seen after 1 day of total sleep deprivation.
○ The important aspect of these results is that the rise in error rate for any of the sleep-restricted groups showed no sign of a plateau. The trajectory was a straight line of continuing decrement in performance.
○ Further, the groups did not recover to baseline after even 2 nights of unlimited recovery sleep.
￼• Two important results from this study are that sleep debt is cumulative and that 1 or 2 nights of recovery sleep do not return vigilance to the optimal level. Further experiments by Dinges also found that not only did the recovery from 2 weeks of restricted sleep require multiple days, but the susceptibility for further impairment was elevated even after the allowed 3 days of recovery.
Understanding the role of sleep can help in treatments for post- traumatic stress disorder (PTSD). PTSD is an anxiety disorder that results from a severely traumatic event, such as a life-threatening accident, sudden death of a loved one, natural disaster, or terrifying personal attack.
Typically, vivid memories of the event will recur, sometimes triggered by some specific stimulus. The individual will be hypervigilant and will try to avoid situations that might trigger the mental playbacks. Sufferers also experience terrifying nightmares.
PTSD involves overactivity in circuits in the hippocampus, amygdala, and frontal cortex. It can be thought of as superconsolidation of the memory and its emotional valence. As a result, this emotional memory is not only resistant to extinction, but it may even strengthen with time.
If PTSD stems from a REM sleep disorder, we should be able to treat it through sleep.
○ The hypothesis here is that in PTSD, traumatic nightmares
are so severe that they arouse the individual from sleep. The individual then replays the dream in the waking state, which is almost like reexperiencing it. If he or she then goes back to sleep, that new version of the memory gets consolidated.
○ However, we may be able to use these same mechanisms to cure the problem by altering the memory that is reactivated and by interfering with reconsolidation.
Sleep in the Future and the Future of Sleep
○ This hypothesis is consistent with ideas about the process of memory consolidation during sleep. If a memory is selectively and repeatedly reactivated during sleep, it should be selectively and repeatedly reconsolidated and, therefore, strengthened.
○ However, sleep fragmentation following learning disrupts memory formation. This effect is presumably because of interference with the memory consolidation. It may be possible to use reactivation during sleep to weaken the emotional valence of the memory.
Sleep and Learning
Learning during sleep is an intriguing possibility. When portable tape recorders were first introduced, the idea was that if you played, for example, a foreign language tape while you slept, you would learn the language.
These attempts were not successful at the time—perhaps because the memory transcript was not there to be reactivated. But now that we know specific memories can be reactivated and strengthened during sleep, the possibility of sleep learning should be reinvestigated.
Language learning might be an excellent research focus. As with the experiment in which sounds were paired with images, here, the sounds could be the spoken words. If a student studied a list of phrases in a foreign language and then some of those phrases were replayed during sleep, they might be more likely to be recalled during the subsequent day.
Language learning is a mixture of procedural and declarative memory formation, so it would also be of interest to see whether reactivation during sleep is effective for both types of memory alone.
○ In experiments using the computer mouse to move a cursor on
the screen to a target, clearly, performance improvement on that task was a function of nonREM slow-wave activity in the appropriate region of the motor cortex.
￼○ That activity might be stimulated during sleep by a cue that reactivates the memory. Researchers in the lab of Robert Stickgold are studying how the skills of subjects in a virtual reality task—downhill skiing—are improved during sleep. The researchers are also correlating the subjects’ reports of dream imagery with the observed improvements.
○ The indications are that the experience of training before sleep is reflected in mental processes during early sleep. In any of these experimental paradigms, it would be of interest to have multiple tasks associated with different stimuli to see if they could be selectively improved during sleep.
A recent study in Israel showed that humans can acquire new information during sleep, at least at the level of conditioned reflexes.
○ When humans experience a new odor, they sniff. If the odor
is good, they sniff deeper, and if the odor is bad, they sniff more shallowly.
○ The investigators introduced good and bad odors to subjects during sleep and paired them with tones. They showed that during sleep, the subjects learned to associate the tones with deep or shallow sniffing responses.
○ Training in early sleep resulted in appropriate responses to the tones during late sleep. The conditioning during nonREM sleep carried over to subsequent wake.
• Experiments in slow-wave activity—the nonREM processes apparently involved in memory consolidation—have indicated that potentiating slow-wave activity improved learning. Also, slow- wave activity can be enhanced with drugs that mimic the action of adenosine. What is the possibility that we could we speed up the rate of training and learning by enhancing the quality of sleep or make sleep more efficient so that we could get the benefit of 8 hours of sleep in 6 hours?