by Aaron Wintrich

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Fear In Dreams Caused By Stressful Stimuli On The Amygdala During Waking Life

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Why do we dream? The answer to this question has a long evolutionary story. During the time when the earliest mammals walked the Earth we see a distinct physiological difference from their reptilian and amphibian cousins. All of these species had a common ancestor, however mammals were unique. Reptiles did not evolve to have as developed amygdaloid complex as mammals, which is a brain structure responsible for emotions and works together with the hippocampus which converts short term memory into long term memory. Both the amygdala and hippocampus work together to create and link emotional experiences to memories. We can understand the importance and relevance of this process to dreams by explaining the evolutionary story of the brain and how these neurological features evolved. The greater development of the amygdala found in mammals comes from their nose which is directly linked to the amygdala. Mammals have the greatest sense of smell in the animal kingdom because they typically hunt at night and so evolved a necessary nose and sense of smell to find food to compensate for not being able to see in the dark. Therefore, as mammals olfactory senses evolved into better developed systems, so then did their amygdala. This is also why the sense of smell in humans is our greatest trigger for recalling past memories. In comparison to reptiles, we can see how this neurological difference is reflected in mammals behavior. For example, when reptiles reproduce they typically do not form lifelong pair bonds with their mates and lay multiple eggs which they then leave to fend for themselves. Mammals on the other hand in many cases do form lifelong pair bonds, have fewer children and rear their young until they are matured enough to survive on their own. Mammals develop such bonds with their mates as well as with their young because, unlike reptiles, their higher developed amygdala-hippocampus complex allows them to convert short term memory into long term memory more effectively and attach feelings to those memories which allows them to recall with whom they successfully mated. Also we can see that memory as a trait increases mammals chances of survival over reptiles because they can remember to avoid negative stimuli previously experienced through recall of those past dangers rather than simply reacting to it based on its immediate experience. We can also see the importance of this in child rearing as a mammalian mother’s memory and emotional love for their young increases the chances of their child’s survival through territorial and protective behavior, and as all life strives to survive and reproduce, traits that increase these possibilities are selected. Both of these behaviors are evolutionary advantages for an individual’s and therefore a community’s survival and it is these same behaviors that humans have inherited from our early mammalian ancestors. But how exactly does memory work and how does this benefit us through dreams? It works in part through what is known as neuron oscillation. As an electrical impulse in the brain is triggered from an external experience, such as a light wave transmitted through the eye, which will oscillate around the neuron at the same frequency as the incoming information’s wavelength, molding the neuron into a shape and connection with other neurons to retain the information of the experience. However, in order for the memory to “stick” it often needs an emotional reinforcement, i.e. the amygdala. We remember things that create an emotion in us, avoiding things that cause negative emotions and seeking out ones that cause positive ones, and this is what the amygdala does. To increase our survival we link emotions to memories, memories like that of tornadoes, sharks, and aliens from watching too many horror movies, to the emotion of fear. We create these memories and relate them to fear so that if we experience them again in the future we can preemptively run and hide before they get too close so that we survive. And in order to further the growth and reinforcement of these memories so that they “stick”, we sleep and we dream. Cellular division and cell reproduction occurs the most while we sleep, obtaining building blocks from the digested food we eat to create new cells. We experience dreams as a byproduct from the growth and creation of these new brain cells while we sleep and the connections they make with other cells as an evolutionary advantage we have over other organisms to reinforce the memories of our waking/conscious life into our subconscious and therefore enhance our probability of survival.

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