Dreaming is a complex state of consciousness that involves many parts of the brain. The neuroscience of dreams involves stronger brain synchronization and higher levels of activation than the waking state. Aspects of dreaming such as bizarreness, vivid imagery and intense emotions are integrated into a conscious narrative expressed through language. However, many parts of the brain involved in dream creation are low and mid-brain structures.
Brain Activation During Dreaming
Most remembered dreams take place during rapid-eye-movement (REM) sleep. In REM, most of the body's voluntary muscles are halted, except for the eyes, preventing us from acting out dream behavior. During dreams, the brain is not at rest, which explains why REM is also called paradoxical sleep. REM is as active as the waking state in terms of electrical activity and sometimes is more active. Brain activity is also highly synchronized across the two hemispheres, specifically in the 40HZ band, linking dream cognition with other highly withdrawn states of consciousness such as meditation.
Lack of Judgment and Volition
Dreams lack active thinking and questioning, compared to waking states. Recent studies with positron emission topography (PET) scans show that these higher brain functions are disabled because the prefrontal cortex is depressed during dreaming sleep. Without these executive functions, thinking is characterized by a "go with the flow" attitude about what you are experiencing in the dream.
Lack of Critical Thought
This lack of critical thought is one reason why dreams are so bizarre. According to dream researcher Alan Hobson, we do not notice when a dream shifts from scene to scene. Some of these seemingly random scene changes in dreams are due to strong electrical pulses from the brain stem, the oldest part of the brain.
Meanwhile, activation in the visual centers of the brain, such as the parietal lobes, creates powerful visual and spatial imagery that is more vivid than much of the information taken in from the senses when awake. Dreaming is almost identical to schizophrenic psychosis as well as religious visionary experience.
Strong Emotions and Memory
Dreaming is also characterized by strong emotions and strange memory combinations. Those powerful emotions are triggered by the limbic and paralimbic structures in the brain, including the amygdala, which is responsible for feelings of fear, anger and anxiety. Overwhelming emotions are triggered at the same time that working memory, also known as short-term memory, is disabled. For reasons that are still debated, long-term memories are emphasized during dreams. Many dream researchers, such as Allan Hobson and Eugen Tarnow believe that dreams are consolidating memories, integrating new experiences with older ones. Others, such as Francis Crick, believe that dreams are an "unlearning" process akin to a memory dump, and are best not remembered at all.
References
- "Dreaming: An Introduction to the Science of Sleep," J. Allan Hobson, 2002
- "The Neuropsychology of Dreams: a Clinico-anatomical study," Mark Solms, 1997.
- "Soul, Psyche, Brain" From Chaos to Self-organization, David Kahn, 2005
