What is High Quality Sleep?
The usual concern about quality of sleep centers on the number of hours needed between hopping in bed and bounding up in the morning. As we all know, this number usually hovers between six (at the low end) and eight (at the high end). We also know that most Americans (and those residing in many other countries) tend to get too little sleep – often 4-5 hours per night. The sleep debt accumulates, like the national financial debt, and the alarms periodically sound in the national media: “We need to get more sleep!” However, high quality sleep is defined not just by number of hours in bed, but also by three other factors: (1) depth of sleep, (2) amount of sleep disruption, and (3) amount of “sleep” engaged at times other than at night. Let’s briefly look at each of these.
Depth of Sleep
First there is depth of sleep. Typically, when we fall asleep, we move slowing down through what are called stage one, stage two and stage three sleep—to arrive at stage four. This stage is often called delta sleep because the brain waves (EEG recordings) resemble the Greek letter delta (slow upward spikes). This is the stage where our body seems to be doing a whole lot of physical restoration. It is sometimes called “the working man’s sleep” because of this supposed physical restoration. Unfortunately, as we grow older, this fourth stage of sleep becomes less frequent and will slowly start to deteriorate as we age. often vanish all together by the time we hit our 50s.
Usually, a remarkable thing happens after several hours. We slide (or leap) up to a unique stage that is called REM sleep. This label is attached because it is during this stage that there are rapid eye movements (REMs). These eye movements rarely occur during the other sleep stages—that is why these other stages are given an additional label: NREM (non-REM). It is also during the REM stage that dreams often occur. After this first (often short) REM stage, we will slip back down to stage four – or more likely stage three. This third stage, often called gamma sleep, is likely to last for a longer period than the previous delta sleep and is a bit more often found among older adults. like myself. We don’t know much about gamma sleep – it is often identified as the “least interesting” sleep stage. But we do know that this stage is just as important as the three more “glamorous” stages. Gamma sleep typically manifests brain waves that are shorter and faster with lower spikes than delta sleep.
After an hour or two we once again shift to REM sleep and experience more dreams – which are often more colorful and somewhat longer. Typically, people do not recall dreams occurring during the middle of the night when they awake in the morning. They only recall these dreams from the middle of the night if the dream has awakened them (for example, a dream that is filled with anxiety) and the dreamer writes something down about the dream. Usually, the dream is not recalled in the morning even if it wakes us up. All we remember is that something disturbing, eventful or (sometimes) joyful occurred during the middle of the night.
Now we are entering the second half of our sleep night. It is common for us to slip back down to NREM sleep after we have been in bed for 3 or 4 hours. At this point, we are most likely to enter Stage Two (beta sleep), which is typified by shorter amplitude and even less-extreme peaks in EEG patterns. We also find increases in the Stage One sleep which generates something called “sleep spindles” (bursts in electronic activity). This high alpha and low beta state can be compared to the state of cortical activity found among people who meditate or engage in other forms of mindfulness.
It is during the last hours of sleep (when both the first and second stages are dominant) that we find the greatest amount of REM sleep. This has been the “pot of gold” for dream researchers. These three stages (One, Two and REM) tend to interweave and many dreams of considerable length and colorful detail are produced. These later night dreams are often the ones we remember when we awake in the morning.
It is also important to note that this interweaving of these three stages is particularly prevalent as we grow older. These are interesting tradeoffs as we age and may have significant implications for our own physical and mental health. What does all of this mean? The pattern of sleep stages is an important factor in determining quality of sleep – it is not just the amount of time we spend in bed.
Amount of Sleep Disruption
This third criterion of sleep quality is particularly important for those of us who are a bit (or a whole lot) older. It also is a criterion that is somewhat controversial—not as straight forward as the stages of sleep. Put simply, sleep disruption is about the number of times we wake up during the night and the amount of time we stay awake during the night. The critical questions to ask are: Is our sleep fragmented with many periods of wakefulness? Do we make infrequent (or frequent) decisions to get up out of bed and do something else – a midnight snack, a few minutes (or hours) or reading or watching TV, even getting a breath of fresh air by walking outside for a couple of minutes.
As we grow older, the tendency in our sleep pattern is to experience at least one major break. We sleep for part of the night and then wake up. We can’t fall back to sleep right away, but either lie in bed, frustrated by our inability to fall back asleep, or we get out of bed and perform our mid-evening ritual. Then, at some point we do return to our bed and fall asleep or we have remained in bed and eventually drift off to slumber land. The critical issue is often how we manage this bridge between the two sleep segments.
For many of us, the sleep bridge plays a central role in determining the quality of sleep. Experts in the field of sleep improvement are still at a loss regarding how this bridge can be successfully crossed in the minimum amount of time. We hope eventually to find answers to this sleep bridge challenge, but at the present time can only offer some recommendations. These helpful suggestions are made by folks who have found their own unique way of crossing (or at least navigating) the bridge—be it by consuming certain foods, moving between hot and cold sleep environments, or engaging in certain kinds of visualization). So, stay tuned . . .
The broader issue regarding sleep disruption is identified as sleep fragmentation. We don’t just wake up once in the middle of the night; rather, we wake up many times and might even find ourselves sleeping “fitfully.” Our night seems to be an ongoing dance between wakefulness and sleep. This might mean that we are spending most of our night in stage one, stage two and REM sleep. It might also mean that we are spending a large amount of time in the pre-sleep and post-sleep states of sleep limbo that are called hypnagogic (pre) and hypnopompic (post). These intermediate states are often filled with very loose (disorganized) thinking, vague images (such as our legs and feet seemingly to grow larger or smaller, our arms appearing to become numb), and/or a swirling of various feelings.
In general, these fragmented sleep conditions are judged to be negative and quite unhealthy. But this isn’t the conclusions reached by all sleep specialists. Some of these experts point out that deep, uninterrupted sleep was not common among our ancient relatives. When our ancestors were living on the Savannah in Africa, it was important to remain alert to some extent in monitoring one’s environment. So that a great night of sleep is not being interrupted by a lion who is eating us! We had to be aware in some way of the potential dangers surrounding us on the Savannah—or we belonged to a tribe in which one or more members remained fully awake during portions of the night. They served as watch guards—keeping alert to potential dangers from other tribes or human-eating animals. It is interesting to note that some animals can actually sleep half of their brain, while remaining awake with the other half. Unfortunately, humans have not been blessed with this capacity. Instead, we either need to remain somewhat wakeful or be the member of a well-organized tribe with an effective watch guard system in place.