In this series, I dig a little deeper into the meaning of psychology-related terms. This week’s term is sleep. It’s something we all need to do, but what exactly is it?
Sleep involves altered consciousness and decreased reactivity to sensory stimulation from the environment. The brain’s energy consumption drops significantly, which allows for the repletion of adenosine triphosphate (ATP), a key form of fuel in the brain. The brain also produces more neurotransmitters.
The immune system, nervous system, muscles, and bones shift to an anabolic state, which involves building back up what might have been broken down (through the process of catabolism) during the day. Certain hormones, such as growth hormone and prolactin, are secreted during sleep.
REM & non-REM phases
There are two key phases of sleep: rapid eye movement (REM) and non-REM.
The non-REM stages, including the deep sleep phase, are a very quiet time in the brain. In the first (and lightest) non-REM stage, people will sometimes experience “hypnic jerks”, sudden muscle contractions preceded by a feeling of falling.
During slow wave sleep, the deepest non-REM stage, it’s very difficult to rouse someone, and if awoken during that stage the person will feel groggy and there will be some level of impairment for about half an hour. The time spent in slow wave over the course of the night decreases with age.
The REM phase, on the other hand, is a very active time. Besides the rapid eye movements that give this phase its name, the electrical pattern on an EEG (electroencephalogram) is very similar to what’s seen in someone who’s awake. However, the muscles throughout the body are mostly immobilized. Breathing becomes more irregular, and heart rate may increase. Dreaming occurs primarily during the REM phase, and more time is spent in REM during the later part of the night.
Long-term memory formation occurs while asleep, with the consolidation of declarative memory (information about things) occurring mostly during non-REM and procedural memory (how to do things) being handled mostly during the REM phase.
The body’s natural circadian rhythm has a significant effect on the timing of sleep-wake cycles. The suprachiasmatic nucleus in the brain plays a major role. It gets signals from light receptors in the retinas of the eyes. The pineal gland in the brain secretes melatonin, which is also an important part of this system. The circadian rhythm also affects the secretion of cortisol and certain other hormones.
Sleep deprivation has both mental and physical effects. It increases the risk for type 2 diabetes, affects the release of the stress hormone cortisol, and has negative effects on memory and attention.
In a study involving lab rats, the rats died after 5 weeks of sleep deprivation. Sleep deprivation is sometimes used as an interrogation technique. The longest scientifically documented period a human has stayed awake without stimulants is 264 hours (11 days), while the Guinness World Record is 18 days, 17 hours.
Sleeping is essential for everyone, but for those of us living with mental illness, it’s even more important. It was only when depression first hit that I started having insomnia; before that, I was a great sleeper, which was certainly handy on long flights. Now my illness isn’t well enough controlled to be able to manage without sedating meds. Working can throw everything off, and sometimes driving home from work I’ll need to have the window open and music blaring to keep myself awake. The more days in a row I go without sleeping enough, the stupider I get.
Is sleep something you’re able to get enough of?
You can find the rest of the what is… series in the Psychology Corner.
- American Sleep Association: Sleep deprivation, Stages of sleep, What is sleep?
- Wikipedia: Sleep, Sleep deprivation