Sleep Care

The Dream Series, Part 4: The Evolutionary Perspective

Have humans always been able to dream? While it may seem an unusual question to consider, from an evolutionary perspective, we haven’t. Finnish neuroscientist Antti Revonsuo notes that when we dream, the brain builds a very realistic model of the world where some elements occur less frequently than they do in everyday life, and others appear more often. Additionally, the content of dreams is consistently and significantly changed by certain types of experiences when we’re awake. Using these observations, and evidence gathered from a variety of other sources, Revonsuo developed the Threat Simulation Hypothesis of dreaming. The Threat Simulation Hypopthesis of Dreaming Unlike the emotional functions of dreaming from a psychological perspective, the Threat Simulation Hypothesis assigns a biological purpose to dreaming: the realistic rehearsal of threats that may be faced while awake, which improves the odds of survival and producing children to continue the species. Although the body’s muscles are typically paralyzed while dreaming, the brain’s activity level is comparable to when a person is awake—meaning that how the brain responds to events in a dream is similar to how it will respond when the person confronts the situation while awake. This principle is often used by athletes who mentally rehearse successfully competing over and over again (during both waking and dreaming states) to further train their bodies for competition. In a similar manner, those human ancestors who developed a capacity for dreaming would have a survival advantage over those who did not because they’d be rehearsing survival techniques and solving problems while asleep. Evidence From Several Different Areas Support for an evolutionary approach to dreaming comes from a variety of sources, according to Revonsuo. All the senses—sight, hearing, touch, etc.—are present in dreaming at approximately the same frequencies they’re used during waking consciousness. Threatening events and negative emotions tend to be occur more often in dreams than they do naturally during the day, suggesting frequent unpleasant content (such as the threats that one must navigate for survival). Children’s dreams show a much larger number of animal characters than adult dreams, and they are more likely to be perceived as wild or threatening in young children—which makes sense if our ancestors’ dreams trained them for how to deal with the untamed animals of that era. Among adults, the most common type of recurring dream is one in which the individual is being pursued or chased, a common dilemma for primitive humans. What Does This Mean For People Today? Of course, the environment today is much different than that face by our human ancestors. Does this mean that dreaming doesn’t have much of a purpose for modern people? Not necessarily. While dreaming may not directly enhance one’s chances for survival as it did for our ancestors, the idea that it serves as a “rehearsal” for situations faced during waking consciousness can have useful applications. One of these might be athletes training for a competition, as mentioned earlier—or anyone who wants to build their confidence for performing a task by “practicing” it mentally while dreaming. It might also be helpful for soldiers or those who may undergo potentially traumatic events in the course of their jobs, such as firefighters or police officers. Research investigating nightmares of those suffering from post-traumatic stress disorder has found one key aspect to how frequently they occur is the degree to which the danger in the dream is perceived as being targeted to the dreamer or to someone significant to them. This makes sense when viewed from the Evolutionary Perspective on dreaming. Treatment for these individuals can effectively use image rehearsal therapy as a way to rewrite the storyline for the dream and enable the dreamer to survive. Look back at Parts 1-3 of the Dream Series. Part 1: The Psychological Perspective

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Part 2: The Neurological Perspective Part 3: The Developmental Perspective  

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