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*This week is Brain Awareness Week. Every day this week, prominent researchers from the International Association for the Study of Dreams are reviewing their work on dreaming and the brain. You can access and download their articles for free on the IASD website (link).*
*For a graphical PDF of this article click here.
Our brains cycle through four stages during sleep, each characterized by unique patterns of brain waves—the electrical pulses generated by neurons communicating. Slower brainwaves are indicative of deep sleep or meditation or when we feel tired or sluggish, higher frequencies are prominent in alert and awake states. Researchers use Electroencephalography (EEG) to record this brain activity through electrodes placed on the scalp.
As we move through four stages of sleep, brain activity becomes slower and more synchronous:
- Stage 1 is a very light sleep that is mixed with wake-like alpha waves (8-12 cycles per second)
- Stage 2 is a slightly deeper sleep with slower theta waves (5-7 cycles per second)
- Stage 3 is the deepest sleep and is marked by slow delta waves (0-4 cycles per second).
- Finally, we enter REM sleep, a period marked by “Rapid Eye Movements (REM),” in which brain activity increases to wake-like levels, though the rest of the body is essentially paralyzed.
Dreaming through the sleep stages:
Stage 1
- Stage 1 dreams occur in the foggy state just as you fall asleep, nod off for a second, or just as you wake up.
- Stage 1 dreams are usually very brief, but often have vivid visual or visceral content, such as the common sensation of ‘falling’ to sleep.
- Because the brain is still somewhat awake, these dreams frequently incorporate real-world stimuli, such as an alarm clock or a barking dog.
Stage 2
- Stage 2 dreams are often brief, and incorporate fragments of recent waking life
- Stage 2 dreams are commonly described as ‘thoughtlike’, they may feel simply like thinking during sleep
- However, as the night goes on, Stage 2 dreams gradually become longer and more vivid.
Stage 3
- Dreams are the least vivid from stage 3 deep sleep, although they do occur.
- Early researchers believed it physiologically impossible for any cognition to occur in deep sleep.
- Today, researchers acknowledge that even in deep sleep the brain is active, processing memory and restoring cognition.
REM Sleep
- REM sleep dreams are the typically the longest, most vivid and bizarre dreams.
- Because we have a lot of REM sleep in the morning, these are the types of dreams that people most often awaken from and remember in their daily life.
- The emotional parts of the brain are most active during REM sleep (see below). This likely is part of what makes REM sleep dreams so emotional and meaningful.
Dreaming and the brain
The content of dreams is largely provided by the cortex, where we house the myriad memories of our autobiographical lives: friends become dream characters, TV shows become dream settings.
Sensory cortices are also active in providing perceptual details, especially visual and auditory cortex, although a small portion of dreams contain smell or taste.
The motor cortex, which controls our movements in waking life, is also active. In fact, neuroimaging has shown that brain activity is similar during dream actions and waking actions. So, practicing a sport in dreams may give you an edge come game day.
The limbic system is also active in REM sleep, and is responsible for dealing with emotions. REM sleep dreams are thus more emotional than dreams from the other stages.
Unusual dream experiences in the brain
Lucid dreams, where the dreamer is aware that they are dreaming, are characterized by increased prefrontal activity during REM sleep. Because of this, the dreamer has cognitive abilities similar to waking life, including voluntary control of thoughts and actions.
Nightmares are a form of emotionally intense and arousing dream that often result in a sudden awakening. These dreams also occur most frequently in REM sleep. However, contrary to lucid dreams, nightmares seem to be characterized by decreased prefrontal activity, which leads to inadequate control of emotion, and overwhelming arousal.
