What is Sleep?
For years, most people thought sleep was a passive, dormant part of our daily lives. They thought sleeping, simply meant “resting” so we can be recharged for the following day. While this is true, there is a lot more to it. Our brains are very active while we are asleep. Sleep is a condition of the body and mind that typically occurs for several hours every night. When this occurs, our nervous system is relatively inactive, our eyes are closed, the postural muscles are relaxed, and our consciousness is practically suspended. Sleep affects our daily functioning, and our physical and mental health. It is essential to maintain normal levels of cognitive skills such as speech, memory, and innovative and flexible thinking, and plays a very significant role in brain development.
There are neurotransmitters (nerve signaling chemicals) that control whether we are asleep or awake, by acting on different groups of neurons in the brain. Neurons in the brain stem produce neurotransmitters such as serotonin, that keep some parts of the brain active when we are awake. There are other neurons at the base of the brain that begin signaling as we fall asleep.
While we are sleeping, we go through five different stages of sleep. Four are referred to as “Non REM” (stages 1, 2, 3, & 4) sleep, and then there is the last stage, REM (Rapid Eye Movement) sleep. Of our total sleep time, about 50% is spent in stage 2, about 20% in REM, and the remaining 30% in the other stages. A complete sleep cycle takes about 90 to 110 minutes to complete. The first sleep cycles of each night usually have relatively short REM periods and longer deep sleep (stages 3 and 4). However; as the night progresses, our REM periods become longer and our deep sleep stages decrease. By morning, we spend almost all of our sleep time in stages 1, 2, and REM.
As we move through these 5 stages of sleep throughout the night, different brain waves become dominant. At the root of all behaviors, feelings, thoughts, and emotions, is the communication of neurons with the brain. Brain waves are produced by synchronized electrical pulses from masses of neurons communicating with each other. Brain waves change according to what we are doing and feeling. When the slower brain waves are dominant we feel tired, lazy, or sluggish. When the higher frequencies are dominant, we feel hyper or wired. Brain wave speed is measured in Hertz (Hz) and are divided into bands, delineating slow, moderate, and fast waves.
The lowest brain waves are called Infra-low (<.5 hz). These are thought to be the basic rhythms that underlie our higher brain functions. Their very low frequency nature makes it hard for them to be detected. Delta waves (.5 to 3 hz) are slow brain waves generated in deepest meditation and dreamless sleep. Theta waves (3 to 8 hz) occur most often in sleep, but are most present as we drift off to sleep, or as we begin to wake up. Alpha waves (8 to 12 hz) are present in quietly flowing thoughts and in some meditative states. This is a resting state for the brain. The Beta waves (12 to 38 hz) are visible in our normal waking state of consciousness when attention is directed towards tasks and the outside world. Beta is fast activity that is present when we are alert and attentive. The highest frequency wave is the Gamma wave (38 to 42 hz). This wave is the fastest of waves and relates to simultaneous processing of information from different areas of the brain. This is the most subtle of brain wave frequencies. This is highly active when in states universal love. Gamma rhythms modulate perception and consciousness, a greater level of these waves relates to expanded consciousness and spiritual emergence.
Stage 1, also known as “light sleep”
is the transition between being awake and being asleep. In stage 1, our brain waves transition from Beta, to Alpha, to Theta. We will typically drift in and out of sleep and can be awakened easily. Our eyes move slowly, and muscle activity slows down as well. In this stage we can experience the sudden muscle contractions called “hypnic myoclonic” often preceded by the sensation of starting to fall.
Stage 2 of our sleep is also known as “true sleep”.
Our eye movements stop, and our brain waves become slower with occasional bursts of rapid waves called “sleep spindles”. In stage 2, Theta waves are mostly present.
Stage 3, is where the “deep sleep” begins.
Extremely low brain waves begin to appear, called Delta waves, interspersed with smaller faster waves. Stage 3 and 4 are both known as this deep sleep. It is typically very difficult to wake someone in these stages. There is no eye movement or muscle activity. In these stages, some children can experience bed wetting, night terrors, and sleep walking.
In REM sleep, our breathing becomes more rapid, irregular, and shallow. Our eyes jerk rapidly in various directions, our limb muscles can become temporarily paralyzed, heart rate and blood pressure increase. When we are woken up from REM sleep, we can often remember our dreams. The brain waves that are dominant in REM sleep are, Theta, Alpha, and Beta waves. There is a mixed frequency of these brain waves. The first REM cycle usually occurs about 70 to 90 minutes after we drift off to sleep. During this stage, signals from the base of the brain travel to a brain region called the “thalamus” which relays them to the cerebral cortex (outer layer of the brain that is responsible for thinking, learning, and organizing information). REM sleep increases the production of proteins that help cell growth, which is why we call it “beauty sleep” and often feel energized and rejuvenated when we wake up after a good night’s sleep.
As demonstrated in this blog, you can see that sleep, is in fact, very necessary for not only our bodies, but our minds to work properly. Sleep is not just “resting” the body and mind for 6 to 8 hours every night. A lot happens in this time, through our change in brain waves as we move through the 5 stages of sleep. Our brains are quite complex!