Dreams

Background

Every night we lay down to rest, we spend about two hours traveling through seemingly real experiences as dreams bubble up from our subconscious during various phases of sleep. 

The origin, meaning, and mechanisms behind dreams have spurred speculation since the dawn of recorded history. Despite the ubiquity of the experience—and the advent of modern medical technology—where dreams come from, and what their purpose is, remains largely unanswered.

Meaning & Purpose

For millennia, dreams have been a prime example of pareidolia—humans' impulse to find meaning in ambiguous images and visual patterns. 

Early history is filled with examples of vivid dreams interpreted as prophecy, divine revelation, or a bridge between the living and the dead. Ancient Babylonians established and left instructions for their complex system of dream reading (see overview).

Sigmund Freud brought dream theory into the modern era at the beginning of the 20th century, arguing dreams were often the fulfillment of unconscious wishes (explore his seminal work on dreams).

Another pioneer in the field, Freud's close colleague Carl Jung, took a different approach. Jung theorized that dream symbolism was pulled from a collective unconscious, reflecting a set of universal instincts and archetypes. 

Beyond their meaning, psychologists have variously suggested the purpose of dreams is to process difficult emotions, consolidate memories, mentally rehearse real-life experiences, or are just a byproduct of the complex brain.   

Inside the Brain

Sleep generally occurs in two types: non-REM and REM (rapid eye movement). Dreaming happens across all types of sleep; however, the majority of dream states unfold during REM phases when the body is paralyzed, with brain waves closely resembling those during waking periods. 

Certain brain regions fire away during REM. In particular, the thalamus (which relays sensory information) sends signals to the cortex (which processes information from memory) encoding images, sounds, and more, mimicking waking states (see overview).

Separately, the hippocampus—the brain's memory center—plays a central role in dream construction. Half of all dreams draw from specific real-life experiences, according to one study, and patients with a damaged hippocampus have been shown to experience less detailed dreams. 

Lucid dreaming, where subjects are aware they're dreaming and can exert control over their actions, is of particular interest. Studies suggest at least eight different brain circuits combine to produce (see Fig. 1) the unique experience, including those shown to play a role in self-awareness and planning. 

Roughly one in 250 people reports having never dreamed at all, though researchers believe such sleepers functionally dream but are prevented from remembering them by some unknown underlying cause.