Why Do We Sleep?

The Many Functions of Sleep

It’s tempting to think that sleep is just about rest, and whilst we do rest at one level, it is also an extraordinarily active process that is built into our biology. Sleep is the period of time in which our biological and psychological systems are renewed, cleaned, integrated and optimized. There is no biological system that isn’t enhanced by quality sleep.

Sleep is daily therapy for the mind and body
There are two very distinct types of sleep, REM (Rapid Eye Movement) sleep and non-REM sleep, also known as Slow Wave Sleep (SWS). Our brains need to cycle through both. Approximately every 90 minutes, we cycle from non-REM to REM. In the first half of the night, the majority of those 90-minute cycles are composed predominantly of deep sleep. In the second half of the night, we have much more rapid eye movement sleep.

REM Sleep
REM sleep is the phase in which dreaming occurs and occurs about 90 minutes after falling asleep. Eyes move rapidly behind closed eyelids, breathing becomes faster and irregular and brain activity resembles wakefulness. Despite the body's stillness (its anti-gravity muscles are temporarily paralyzed) the brain's neocortex (associated with higher brain functions such as abstract thought and problem-solving) and emotional centers are highly active. In REM sleep large amounts of the brain's energy reserves are expended on dreaming. We will come back to dreaming shortly.

Non-REM Sleep
Non-REM sleep is characterized by a slow wave pattern on the EEG. It is divided into stages 1—4 which show an increasingly slow wave pattern and represent an increasing depth of sleep.

Stage 1 is the lightest stage of sleep where brain waves begin to slow down into alpha waves. This typically lasts a few minutes. It is easy to be woken from this stage.

Stage 2 is a period of light sleep in which brain wave activity moves towards the deeper slower theta waves. This stage lasts around 25 minutes. In this stage, your brain produces “sleep spindles,” rapid bursts of high-frequency (around 11-16 Hz) brain wave activity that plays a role in memory consolidation (especially memories of cats and events) and learning.

Stages 3 and 4 are the deep stages of sleep, from which it is difficult to wake. These stages are often referred to as “slow-wave sleep” because of the slow low frequency (0.5–4 Hz), high-amplitude fluctuations called delta waves. In deep sleep our learnings from the previous day become cemented into the neural architecture of the brain and our memory systems are reset so they can absorb more information for the day ahead. Impaired memory is a symptom of disturbed sleep. An adequate amount of time in deep sleep is essential for physical recovery and restoration and to recharge energy.

Why We Dream

Have you thought about the purpose of dreaming? It turns out it has a very important purpose. Ivan Tyrrell, a co-founder of the Human Givens approach and the author of "Why We Dream," offers a unique perspective on the purpose and function of dreaming. I trained with the Human Givens Institute and deeply appreciate their enlightened, comprehensive and practical approach to supporting emotional health.

According to Tyrrell, dreaming is a crucial psychological mechanism for maintaining emotional health and one of the primary functions of dreaming is to metaphorically "de-arouse" emotional arousals that have not been acted upon during the day. Essentially, dreams serve to discharge emotional arousal that has not been expressed or resolved in our waking hours. This process helps prevent an overload of unspent emotional arousal. While discharging excess emotional arousal, dreaming also helps in the consolidation of new learning and experiences. It integrates new material with existing knowledge and memory, aiding in problem-solving and cognitive processing.

His work also aligns with the expectation fulfillment theory of dreaming, which suggests that dreams are a way of fulfilling unmet expectations on a symbolic level. When we sleep and dream, the brain is essentially 'acting out' these unmet expectations through the dream narrative. This process helps to reduce emotional tension and restores the brain’s capacity for clear thinking and good mental health. In this context, dreaming is seen as an essential process for maintaining mental health. When the dreaming process is disrupted or overloaded (as in the case of extreme stress or trauma), it can lead to various mental health issues, such as depression, anxiety, or PTSD. If you want to learn more I highly recommend his book.

What are the functions of sleep?

It’s worth taking a minute through these so you can appreciate just how important sleep is!

Restoration and Repair:
Sleep allows the body to repair and rejuvenate itself. This includes muscle growth, tissue repair, protein synthesis, and growth hormone release.

Brain Function and Cognitive Health:
Sleep is crucial for cognitive functions such as memory consolidation, learning, problem-solving, and decision-making. During sleep, the brain reorganizes and recharges itself, removing unnecessary information. REM sleep, as I mentioned before, enhances learning and memory processes and contributes to emotional health.

Emotional Well-Being:
Sleep helps regulate mood and is associated with improved emotional resilience and mental health. Lack of sleep can affect judgment, mood, and the ability to learn and retain information.

Physical Health:
Sleep is involved in the healing and repair of the heart and blood vessels, playing a critical role in cardiovascular health. Adequate sleep maintains a healthy balance of the hormones that make you feel hungry (ghrelin) or full (leptin) and regulates insulin levels.

Immune Function:
During sleep, the immune system releases cytokines, some of which help promote sleep. Certain cytokines need to increase when you have an infection or inflammation, or when you're under stress. Sleep deprivation may decrease the production of these protective cytokines.

Detoxification:
The glymphatic system, more active during sleep, helps remove waste products from brain cells. This is crucial for brain health, potentially playing a role in preventing neurodegenerative diseases.

Conservation of Energy:
Sleep reduces energy demand during a part of the day when it’s least efficient to hunt for food. It helps conserve energy resources.

It’s clear and compelling. Getting enough sleep (7 - 9 hours most nights) and getting enough quality, undisturbed sleep is essential for health, wellbeing and performance.