Humans spend a third of their life sleeping or trying to fall asleep. Sleep deprivation can result in a variety of cognitive problems, such as depressed mood, speech disfluency, reduced alertness, attentiveness, and the ability to learn or remember things. Sleep is essential to our physiological and psychological well-being, as it allows us to recharge overnight in order to face a brand new day with our cognitive abilities intact. So, it seems that sleeping is necessary.
But is dreaming? What even is a dream? And more importantly, what happens to our brain when we dream?
A dream can be defined as a “subjective experience during sleep” that is solely accessible by the dreamer after waking up. Everybody dreams, even if they do not remember having done so. In an average 8-hour-long sleep, we dream for only about 2 hours!
Dreaming mostly occurs in rapid-eye-movement (REM) sleep, but to a limited degree, can also take place in non-REM sleep. During REM sleep, arm and leg muscles become temporarily paralyzed, while the eyes move quickly from side-to-side, and breathing, heart rate, and brain activity increase to nearly-conscious levels. These features have led researchers to characterize REM sleep as a “metabolically awake brain in a paralyzed body.”
Our dreams are not detached from neural activity. In fact, they very much reflect the inner workings of the brain. The sensory perceptions that dominate our wakeful state are also present in most dreams.
Taking The Blue Pill
Consider how dreams tend to be vivid with colour, shape, and movement and incorporate things we are well acquainted with, such as people, places, or animals. Dreams even contain sound and sometimes tactile perceptions such as pleasure, pain, smell, and taste. Unconscious experiences, then, can be “seen, heard, and felt.”
Similar parallels are witnessed in the conscious brain. Electroencephalogram (EEG), which monitors electrical activity in the brain, reveals similar states in the active waking brain and REM sleep. Positron emission tomography (PET) has shown that global brain metabolism in REM sleep is comparable to that of being awake. Remarkably, our visual cortex (responsible for processing visual information) becomes highly activated when experiencing vivid visual imagery while dreaming.
There is also consistency between the cognitive and neural organization of dreaming and being awake. For example, children’s dreams parallel that of their waking cognitive development. Even more remarkable, people with impaired facial perception do not dream of faces.
Most of the time, we lack voluntary control in dreams; things just happen and we carry along with the events that unfold. This could be a function of the right inferior parietal cortex snoozing during REM sleep. This cognitive region has recently been associated with free will (or waking volition).
We also experience altered reflective thought, such that we accept absurd events as true – for example, swinging from the moon as pictured above, or the impossible jarring transitions from one scene to the next. In dreams, we often feel uncertain about time and space, or the identities of the characters that come and go. This could be a consequence of deactivation in a variety of brain regions (such as the dorsolateral prefrontal cortex) during REM sleep. In fact, deactivation of the prefrontal cortex is associated with reduced self-awareness when engaging with highly sensory experiences while awake.
Some of our dreams are highly emotional. We feel the things we dream up, whether this is fear, anxiety, surprise, or joy. Unsurprisingly, then, REM sleep is associated with increased activation of the amygdala, anterior cingulate cortex, and insula; these limbic and paralimbic structures are implicated in emotion, emotion-regulation, and fight-or-flight response. However, in approximately 25% of REM sleep, emotion is absent – even in situations we typically feel something when encountered consciously. Conversely, we rarely experience sadness or guilt, which may be a byproduct of reduced self-awareness.
We don’t always remember our dreams after waking up; dream recall tends to be best following REM awakening and can vary within and between people. Factors such as personality, sleep duration, and visual memory have been associated with dream recall. Several studies even point to sex differences, finding that women recall their dreams more often than men.
Some researchers suggest that just as we need to sleep, so too do we need to dream. They suggest dreaming has a healing touch, reducing the sting of painful waking emotional experiences; that dreaming provides a safe environment to re-process upsetting memories and reach emotional resolutions when we wake up the next day. Maybe, then, an evolutionary function of dreaming is overnight self-therapy.
So, then, what did you dream of last night?