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. A circadian rhythm is one that lasts approximately 24 hours and persists even in the absence of variations in light and dark; can be reset through changing the environmental conditions one is exposed to; and the body adjusts temperature as part of the rhythm. Even certain bacteria display circadian rhythms, so this is not something that’s unique to humans.
Light and dark play an important role in the circadian rhythm. There’s a direct connection between specialized photosensitive receptors in the retinas of the eyes and the suprachiasmatic nucleus (SCN) in the brain. The SCN acts as a regulator of the circadian rhythm, triggering the pineal gland to release melatonin when it’s nearing time for sleep.
I was curious about how this might affect my blind blogging friends, so I did a bit more digging. The specialized ganglion cells that pick up light in the retina are functionally distinct from the photoreceptor cells used for vision, so a small proportion of people who are totally blind and the majority of people who have some degree of light perception maintain a normal light-dependent circadian rhythm.
In mice, mutations in the “clock gene” can lead to overeating and obesity, with increased risk for diabetes. In humans, shift work and other activities that disrupt the circadian rhythm can contribute to weight gain, heart problems, and inflammatory conditions. Excessive screen time on electronics is another factor that can disrupt the circadian rhythm.
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: Circadian rhythm | Sleep | Sleep deprivation
Sleep Better: The Little Book of Sleep is a mini-ebook that covers a range of strategies, both medical and non-medical, to help you get the best sleep you can. It’s available from the MH@H Download Centre.