When Sigmund Freud began investigating dreams 100 years ago, he assumed that dreaming involved many parts of the brain. While the modern science of dreaming has disproved much of Freudian theory, neuroscientists widely accept his central premise that dreams are meaningful expressions of the mind-brain system. The lower, middle and higher brain all contribute to dreaming cognition, making dreams a weird but fruitful object of study.
Lower Brain Causes REM sleep
The oldest part of the brain, shared by all vertebrates, is the brain stem. In 1977, Allan Hobson and R McCarley discovered that electrochemical pulses from the brain stem create the stage of sleep in which most dreams occur. Known as REM, which stands for rapid eye movement, this stage of sleep guides the paralysis of all voluntary muscle groups, except for the eyes. Scientists believe these brain pulses from the pons region of the brain stem may create the seemingly random shifts in dream scenery for which dreams are so well known.
Middle Brain Adds Emotions
When dreaming sleep begins, the middle brain "lights up" with activity. In fact, this part of the brain, which humans share with all mammals, is more activated than in waking life. Also known as the limbic system, the middle brain controls emotional responses and cravings. One organ in the brain is especially active: the amygdala, a walnut-sized mass that philosopher Rene Descartes once thought was the seat of the soul. Today, the amygdala is better called the seat of fear, due to its role in maintaining fight-or-flight responses.
Dream researcher Rosalind Cartwright suggests that dreams are so emotional because we are replaying old memories and updating them with information from recent experiences. It's not straightforward reason but an emotional kind of logic that links all these memories together. Cartwright's laboratory research indicates that most dreams are negative in emotion. The most prominent emotional themes in dreams are fear, anxiety, anger and confusion, providing support for the amygdala's role in the dreaming brain.
Higher Brain Makes Sense of it All
Why don't we realize when dreaming that monsters, ghosts and goblins are not real? In 2002, co-author Allen Braun of the National Institutes of Health published positron emission tomography, or PET, data from the brain scans of dreaming patients clearly showing how the higher brain is largely offline during dreaming sleep. Specifically, the prefrontal cortex that generates language, logic and critical thinking is taking an electrochemical nap while we run away from our nightmare goblins. However, some critical thinking still occurs in dreams, evidenced by the way we create new outcomes in dreams by trying to "work around" the weird plot changes and bizarre visual imagery.
An exception to the lack of executive functioning in REM sleep may be lucid dreaming, which is when the dreamer knows he is dreaming. Validated in the laboratory by Stanford psychophysiologist Stephen LaBerge, lucid dreaming is marked by conscious choices, active thinking and logical reasoning in the dream. This claim is strengthened by researcher Ursula Voss, who along with her colleagues from the Neurological Laboratory in Frankfurt, Germany, revealed that the brain has heightened activity in the frontal and frontolateral areas during these "self-aware" dreams.
The science of dreaming is still in its infancy, but neuroscience has come a long way since Dr. Freud in explaining which parts of the brain create dreams.