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The Science Behind Sleep and Dreams

“Sleep is the golden chain that ties health and our bodies together.” Thomas Dekker

Have you ever thought about how you fall asleep? Are you aware of what changes occur in your body while you sleep, and how the sleep-wake cycle works? Have you realised that the reason you dream involves numerous scientific mechanisms?

The Biochemistry of Sleep

Sleep can be defined as an active state of unconsciousness produced by the body where the brain is in a relative state of rest and is reactive primarily to internal stimulus. Multiple areas in the brain work together to control sleep-wake cycles – thalamus, hypothalamus (contains the suprachiasmatic nucleus, the body’s biological clock, which regulates slow wave sleep along with thalamus), and pons (regulates rapid eye movement- REM sleep).

Nerve cells in the brainstem release neurotransmitters like norepinephrine, histamine, and serotonin, which act on parts of the brain to keep it alert and working while one is awake. Other nerve cells stop the messages that make one stay awake. Adenosine, a chemical involved in this process, works by slowly building up in blood when one is awake, resulting in drowsiness. It slowly dissipates once a person falls asleep.

At the heart of any good night’s sleep is a healthy balance between hormones and neurotransmitters.

  • Serotonin is an important neurotransmitter for regulating the sleep/wake cycle. When its levels are not normal, sleep disturbance and other issues like depression and chronic fatigue syndrome can occur.

  • During the day, the pineal gland is inactive, but when the sun goes down, the pineal gland is timed on by suprachiasmatic nucleus (SCN) and begins to actively produce melatonin which winds the body down to a lethargic and sleep-ready state.

  • Norepinephrine is highly active during wake cycle, slow firing during non-REM sleep and almost completely inactive during REM sleep.

REM and NREM sleep: Sleep cycles repeatedly between 2 phases at intervals- non-rapid eye movement sleep (NREM) and rapid eye movement (REM) sleep.

NREM sleep is associated with slow rolling eye movements. It has several sub-stages, and one of the most important stages is slow wave sleep, where the brain waves are oscillating at a low frequency. NREM sleep is associated with activation of the preoptic area which uses the neurotransmitter GABA and the neuropeptide galanin as its chemical messengers. During NREM sleep, serotonin inhibits acetylcholine signals which support REM sleep.

Usually REM sleep has been associated with dreaming, although some forms of dreaming also take place in NREM sleep. REM sleep is exemplified not only by rapid eye movements but also by a form of movement paralysis – something one can consciously experience if woken suddenly from a dream. Acetylcholine activation of cells creates an oscillating pattern of electrical activity. These waves pass from the pons through to areas of the brain involved in visual processing and help to create the vivid imaginary world which plays out in dreams.

Why do we dream?

A dream is a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep.

A theory says that dreams compensate for the parts of the self and the subconscious mind that do not get expressed during waking life. This theory may be a way for us to interpret the subject matter of our dreams culturally or psychologically.

On the contrary, the continuity theory suggests that although dreams might be bizarre and strange, the person you are in your dreams is largely in line with the person you are in waking life. This theory also maintains that the reactions you have in your dream-space are in line with the way you react to things in real life. It is thus unlikely that the only reason why we dream is to realize or express the hidden parts of the self.

Various other theories about the purpose of dreaming include:

  • Building memory: Dreaming has been associated with consolidation of memory, which suggests that dreaming may serve an important cognitive function of strengthening memory and informational recall.

  • Processing emotion: The ability to engage with and rehearse feelings in different imagined contexts may be part of the brain’s method for managing emotions.

  • Mental housekeeping: Periods of dreaming could be the brain’s way of clearing partial, erroneous, or unnecessary information.

  • Instant replay: Dream content may be a form of distorted instant replay in which recent events are reviewed and analysed.

  • Incidental brain activity: This view holds that dreaming is just a by-product of sleep that has no essential purpose or meaning.

There are a number of things that happen to the body during a dream, including:

  • Rapid Eye Movement: The eyes move rapidly behind the eyelids when one dreams, and do not send visual information to the brain as they usually do in waking hours.

  • Temporary Paralysis: When one enters into REM sleep, the body is mostly immobilized. Almost all muscle tone is lost, with the exception of the muscles under the eyelids and in the diaphragm.

  • Twitching Muscles: It is common for people to involuntarily twitch, especially in the fingers and toes. While twitching was originally thought to be a part of the body’s reaction to happenings within a dream, it may have to do more with processing and mapping the neurons that connect the body to the mind.

  • Breathing Changes: Breathing during REM sleep often becomes irregular, involving dramatic rising and falling.

  • Fluctuating Heart Rate and Blood Pressure: During the NREM stages of sleep, heart rate and blood pressure usually decrease by around 20%

Dreaming can happen during any stage of sleep, but it is most intense during the rapid eye movement (REM) stage. Dreams during REM sleep are typically more vivid and fantastical even though they may involve elements of waking life. The majority of REM sleep happens during the second half of a normal sleep period, thus dreaming tends to be concentrated in the hours before waking up.

“In dreams, we enter a world that is entirely our own. Let us swim in the deepest ocean or glide over the highest cloud.”

- written by Sanjana Mandhan

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