Sleep time – Refreshing mind and body, and consolidating memory.

Sleep is a highly complex and vital process which is essential for the biological balance of the mammalian organism (Benington, 2000), and thought to be critical for homeostatic restoration, thermoregulation, tissue repair, immunity, memory processing, and emotion regulation. Accordingly, sleep deprivation can more lethal than food deprivation.

According to the 2008 sleep in America poll on Sleep, Performance, and the Workplace conducted by the National sleep Foundation, Americans said that they wake up, on average, around 5:35 am on workdays and around 7:12 am on non-workdays. Overall, respondents reported an average sleep time of six hours and 40 minutes on workdays, and 44% get less than seven hours of sleep on workdays. About three in ten respondents (29%) reported falling asleep or becoming very sleepy while they were at work in the past month, and just more than one in ten (12%) were late to work in the past month due to sleepiness or a sleep problem. in the u.s., drowsy drivers are responsible for a fifth of all motor vehicle accidents and some 8,000 deaths annually. it is estimated that 80,000 drivers fall asleep at the wheel every day; 10% of those drivers run off the road, and every two minutes, one of them crashes. A study of work hours, sleep, and depression in 2,643 Japanese citizens who were employed full time showed that participants working more than 10 hours per day, sleeping less than six hours per day, and reporting insufficient sleep were, respectively, 37%, 43%, and 97% more likely to be depressed than those working six to eight hours per day, sleeping six to eight hours per day, and reporting sufficient sleep. The study concluded that depression associated with long work hours is primarily a result of sleep deprivation. These statistics do not take into account the vast opportunity costs that sleep deprivation has on the quality and quantity of performance at work.

Since Aristotle and until the middle of last century, sleep was considered a passive state that simply counteracted sleepiness. Now, half a century later, there is a general consensus that during sleep we not only rest and recuperate strength for the next day, but sleep is also a highly active state that is important for cognitive processes such as memory consolidation, semantic integration, learning, and the processing of emotions.

Generally a distinction is made between two main types of sleep, rapid eye movement (ReM)-sleep and non ReM- sleep. ReM sleep occurs in roughly 90-minute cycles and alternates with four additional stages (stages 1-4, in order of increasing depth) known collectively as non-ReM sleep. slow wave sleep (sWs) is the deepest of the non-ReM phases and is characterized by high-amplitude, low frequency brain oscillations. ReM sleep, on the other hand, is a lighter state of sleep characterized by eye movements, decreased muscle tone (which inhibit the acting out of dreams), and low-amplitude, fast brain oscillations. in fact, ReM-sleep is a neurophysiological state that is more similar to wakefulness than non-ReM states. More than 80% of sWs is concentrated in the first half of the night, whereas the second half of the night contains roughly twice as much ReM sleep than the first half (Figure 1).

Sleep and the body:

One proposed theory of sleep, especially slow-wave sleep, involves homeostatic restoration; that is, after a day of ‘use’, sleep restores chemical and physiological processes that have become depleted during the day. Supporting this idea, the amount and power of slow-wave sleep in the first half of the night is strongly related to the amount of prior sleep and wakefulness, and thereby represents a marker of homeostatic sleep regulation (called ‘Process s’). The more hours spent awake, the more sleep pressure one accumulates and the more intense and abundant subsequent slow-wave sleep will be. This ‘slow-wave sleep rebound’ may reflect a mandatory period of recovery or restoration for multiple biological systems as they recover from the ‘wear and tear’ of waking activities which is an idea supported by the surge in growth hormone that parallels slow-wave sleep early in the sleep cycle. Growth hormone is not only critical in early development, but also in continued growth and maintenance of bone and tissues throughout life.

Sleep and the mind/brain:

As important as sleep is for the body, evidence suggests that it may be even more critical for the brain. There is strong evidence that sleep’s role extends beyond the body and includes critical brain functions, such as memory function, creative processing, and emotion regulation. Recent studies suggest that sleep is critical for solidifying or ‘consolidating’ memories so that we integrate what we learn into long-term knowledge. Recent studies have shown that during sleep, neuronal populations previously engaged in a learning task are reactivated.

This reactivation during sleep is a key process for stabilizing memory traces. Examples include motor-sequence learning, visual-discrimination learning, perceptual learning of language, and declarative memory. For instance, learning to navigate a maze during the day is associated with activation in the hippocampus, which is a structure that is essential for normal memory function. During subsequent sleep, there is a reactivation or ‘replay’ of this hippocampal activation, as if the brain is reprocessing recently learned information. There is a compelling relationship between the increase in hippocampal activation during sleep and the amount of improvement in the maze task the next day. Moreover, if people dream about the maze task, their performance improves still further. This suggests that the re-expression of hippocampal activation during sleep reflects the offline processing of memory traces, which in turn leads to the strengthening of network connections in the brain, resulting in improved memory performance.

ReM sleep in particular has been associated with insight and creativity, which is perhaps not surprising given that the most bizarre, fragmented, sometimes emotional and certainly creative dreams happen during ReM sleep. A recent report shows that a nap with ReM sleep improves people’s ability to integrate unassociated information for creative problem- solving. During sleep, our brains integrate information in highly novel ways and make connections that we are simply not capable of seeing during wakefulness. In addition, several studies have shown that the suppression of sleep produces deficits in cognitive and emotional processing during wakefulness. Even a single night of sleep deprivation can render one more negative and more emotionally unregulated the next day than is experienced with a full night of restorative sleep. Based on this research the expression of “to sleep on it” gains a whole new meaning and the idea that little or no mental activity occurs during sleep is unfounded. instead, sleep is a highly dynamic and active collection of brain states that are critical for physical, cognitive and emotional health.

“The more hours spent awake,
the more sleep pressure one accumulates and the more intense and
abundant subsequent slow- wave sleep will be.”
The Healthy Mind Platter -

But how much sleep should an individual get? It turns out that while the answer is, on average, 8 hours, there is room for individual variation. Sleep need follows a normal distribution or bell curve function with the bulk of individuals requiring seven to nine hours of sleep. However, some individuals require as little as four or as much as 12. While these people are outside the common range of distribution and very rare, they should not be considered to have a disorder.

Understanding one’s sleep needs and ensuring these are managed properly is central to a healthy body, brain and mind. What can one do if short on sleep? it turns out even a short nap can help with studies showing that a day’s worth of sleep need not be acquired in a single nocturnal chunk. Siesta cultures show us that sleep can be divided into a night of five to seven hours and a daytime nap spanning one to two hours. What seems important is that the so-called 90 minute “ultradian cycles” are preserved. Alternatively, however, even very brief naps can help boost cognitive performance and help us feel more alert. in our “sleep-sick” society, napping has become a regular and sometimes necessary part of our daily lives.

Research investigating the benefits associated with napping holds potential for informing workplace practices and individual functioning. In an informative study, assess the benefits of different lengths of naps (5, 10, 20, and 30 minutes). Interestingly, the 10 minute nap conferred the biggest benefit in alertness and performance both immediately after and up to three hours later. The five minute nap was not quite enough to confer a significant benefit while the 20 and 30 minute naps were helpful, but these benefits did not emerge until several hours later, arguably due to the effects of sleep inertia. if one wants the positive effects of a nap right away, a brief nap is most effective. This is because brief naps are more likely to contain light sleep (largely stage 2 NReM sleep), and are short enough to prevent one from delving into slow wave sleep which is restorative but difficult from which to awaken. It is also important to recognize that napping can be learned (with enough practice and diligence); this is key because evidence suggests that regular nappers may glean more benefits from napping than those who only nap out of necessity when absolutely exhausted. Clearly, recent research strongly points to the fact that sleep is far more important than is generally recognized, and though people do not get enough of it, There are easy steps to take to start remedying this problem. Adding a nap to one’s day, or an extra 20 minutes to one’s sleep cycle (or both) can yield major benefits to cognition, emotional regulation and general performance.

Please also read:

• An introduction to The Healthy Mind Platter (1/8)

Source: NeuroLeadership Institute.