We spend about a third of our lives asleep, and exactly why remains something of a mystery. But sleep is an integral part of life, one that has deep and complicated effects on human health and life. In this blog series, I’ve been covering the five stages of sleep—how they happen, what they affect, and how they help us heal.
Sleep Stages 1 and 2
Today, we’ll have a look at the lighter stages of sleep, stage 1 and 2. These light sleep stages are more than a gateway to productive sleep—recent research shows us that they have important impacts on our bodies’ systems.
Stage 1: Slipping Into Slumber
The first stage is the gateway to sleep. In the hypnagogic state, or the state just on the edge of sleep, the body and mind relax from the experience of peaceful but awake alpha brainwaves to longer and slower theta brainwaves, crossing a semi-definable barrier from “awake” to “asleep”. In this state we sometimes experience hypnagogic dreams, those quick and often startling impressions that can shock us awake. This is also the state where some people experience sleep paralysis.
Stage 2: Sleep Spindles and K-Complexes
Stage 2 of sleep also exhibits theta brainwaves, but in stage 2 you also see the occurrence of two unique phenomena in brain chemistry known as sleep spindles and k-complexes. Recent research (which I covered in my blog on sleep spindles and k-complexes back in May) finds that these unique brainwaves alternate as often as every minute or two during stage 2 sleep. Whether a person is very easy to wake from sleep or very difficult to wake from sleep depends on which of the two brainwave patterns is active at the moment, though by all classic definitions they’re spending the whole period in a state of light sleep.
Balancing Internal and External Needs
So why would the brain do this, essentially making sure the body doesn’t react to sound stimuli for short periods during light sleep? It appears to be an evolutionary mechanism for undertaking tasks that shouldn’t be interrupted in the brain in short bursts, insuring that the brain is ready to wake from sleep and respond to external stimuli at least once every minute or so during light stages of sleep. The brain is able to integrate difficult tasks that shouldn’t be interrupted, such as the consolidation of memory or learning (or perhaps signals that regulate the immune or endocrine systems), in a way that still allows for a “check-in” with the surrounding environment every minute or so.
The human brain and the human body are fascinating and complex mechanisms that can’t be considered independently of one another. Sleep is just one more way the brain and body work together to create a uniquely human existence that makes room for the physical, the emotional, and the spiritual in one package.