What scientists have learned about why we dream

Why We Dream: What Scientists Have Discovered

Dreaming remains one of the most captivating puzzles in neuroscience and psychology. Despite decades of research, the question of whether dreams have a definitive physiological, biological, or psychological function has yet to be answered, but that has not stopped scientists from researching and speculating. What has emerged is a rich body of evidence pointing to several overlapping and interconnected purposes.

The Biology of Dreaming: REM Sleep

Scientists propose multiple theories for why humans dream, ranging from psychological functions like processing emotions and unconscious desires to biological purposes including memory consolidation, threat simulation, and preventing cognitive overfitting. While no single theory fully explains dreaming, modern research suggests dreams likely serve several important functions simultaneously, with humans spending approximately two hours per night dreaming during REM and other sleep stages.

Recent research breakthroughs have illuminated sophisticated neural orchestrations that occur during REM sleep, revealing how our sleeping minds process experiences, regulate emotions, and potentially enhance creativity. Contemporary evidence strongly suggests that REM sleep and associated dream activity play crucial roles in memory consolidation, emotional regulation, and creative problem-solving.

Memory Consolidation

One of the most research-supported theories links dreaming to the strengthening of memories. Dreams might function alongside sleep to help the brain sort through information gathered during waking hours, possibly aiding in memory formation and emotional processing. The increase in dream activity is linked to learning new things, suggesting dreams may play a role in converting short-term memories to long-term ones.

Research in the field of cognitive neuroscience has focused on the role of sleep in various neurocognitive processes such as memory consolidation. REM dreams are laden with emotion, and since emotion enhances memory, dream affect may also play a role in emotional memory consolidation.

Emotional Processing and Regulation

Scientists have found strong ties between dreaming and the regulation of emotions. REM sleep plays a pivotal role in the processing of emotional events, and several studies have shown that the consolidation of emotional memories occurs in this sleep stage. Furthermore, experimental deprivation of REM sleep has been demonstrated to compromise the consolidation of emotional stimuli.

Research from the University of California Berkeley Sleep Lab found that "REM sleep and dreaming are essential for emotional regulation and memory consolidation, with dream deprivation significantly impairing the ability to understand complex emotions."

Threat Simulation Theory

The Threat Simulation Theory (TST) states that dream consciousness is essentially an ancient biological defence mechanism, evolutionarily selected for its capacity to repeatedly simulate threatening events. Threat simulation during dreaming rehearses the cognitive mechanisms required for efficient threat perception and threat avoidance, leading to increased probability of reproductive success during human evolution.

Supporting evidence for TST comes from cross-cultural studies. Severely traumatized children reported a significantly greater number of dreams, and their dreams included a higher number of threatening dream events compared to non-traumatized peers — suggesting the threat-rehearsal system activates in proportion to real-world danger.

The Activation-Synthesis Hypothesis

Harvard researchers Allan Hobson and Robert McCarley published a landmark paper in 1977 arguing that dreams are the result of random neural impulses during sleep, and that dreams are simply the brain's attempt to account for these random neural impulses. They viewed the process as physiological, not psychological — dreams as an accidental by-product of the brain activating during sleep. This became known as the activation-synthesis hypothesis.

The Overfitted Brain Hypothesis

A newer and influential theory draws on artificial intelligence for its framework. Erik Hoel proposed that the brain faces a challenge similar to "overfitting" in deep neural networks — when performance on one dataset increases but fails to generalize — and that nightly dreams evolved to combat the brain's overfitting during its daily learning. Dreams are thus a biological mechanism for increasing generalizability via the creation of corrupted sensory inputs from stochastic activity across the hierarchy of neural structures.

Freud, Jung, and Historical Perspectives

It wasn't until the end of the nineteenth century that Sigmund Freud and Carl Jung put forth some of the most widely known modern theories of dreaming. Freud's theory centred around the notion of repressed longing — the idea that dreaming allows us to sort through unresolved, repressed wishes. Carl Jung, who studied under Freud, also believed that dreams had psychological importance but proposed different theories about their meaning.

No Single Answer — Yet

Even with all of the theories and extensive research, "no theory has emerged as to the single reason humans have retained the need to dream." In fact, the evidence suggests all these theories are valid to some degree, intertwined and interdependent. Experts in the fields of neuroscience and psychology continue to conduct experiments to discover what is happening in the brain during sleep, but even with ongoing research, it may be impossible to conclusively prove any single theory for why we dream.