Sleeping and dreaming are thought to play a role in the encoding of memory, both for memories of experiences (episodic memory) and factual knowledge (semantic memory). Have you ever wondered how all of the colourful and varied experiences of life become coded into useful, factual information in the brain?
To take a quote from E.J. Wamsley (Beth Israel Deaconess Medical Center) and R. Stickgold (Harvard Medical School), two neuroscientists, “…the fragmented appearance of recent memory in dream reports, interleaved with remote and semantic content, might reflect the consolidation of recent memories during sleep as they become integrated into older cortical memory networks”
To explore this idea further, perhaps in the process of filing the day’s events into categories and knowledge systems, meanings are extracted that could not have been realized during consciousness. As our recent memories are “placed” within the semantic system, they may become associated with other concepts which, when re-activated through the dreaming process, are multilayered with meaning. To illustrate, what if you had been thinking about this very problem and then went to sleep one night and had the following dream:
In the center of a lush green and flower-filled park children are playing on swings. Their parents are standing around the swings, some pushing them from behind, some observing. In the background, there is some sort of a construction site, but in the next image, a drab concrete building has been erected where the park used to be. The only thing about the park that has been preserved is the swings, which are now indoors, at the center of the building, having been left as a sort of a concession to the public. Parents are still standing around the swings as they did before, and the loss of the beautiful park appears to have been happily accepted by parents and children alike.
Having just recently been pondering issues of memory and dreaming, your interpretation of such a dream might be that our colourful episodic memories are somehow converted into colourless semantic memories through the process of sleep. And yet, the dream outlined above might also represent countless other themes, depending on the dreamer’s additional recent feelings or experiences. For example, this dream might represent the de-humanization of our world and our complacency, the change from youth to old age, from joy to depression, or from trust to cynicism. Our dreams may be packed with meaning because they represent the integration of recent experiences into the “meaning system” which is already established, but which undergoes constant revision as each new day brings new experiences, and with that, the need to understand.
The above quote was taken from The Neuroscience of Sleep, edited by Robert Stickgold and Matthew Walker, 2009 (Elsevier, Inc.)