I Had a Dream, I Think?: The Science of Forgotten Dreams

You wake up with a start and already know you’ll have a good day. The sun is shining, the birds are singing, and your soul has been awash with happiness since last night’s dream. You’ve just had a wonderful dream about–about… erm. 

Even after moments of brain-prodding and mind-poking, you just can’t seem to recall what it was about for some reason. The remnants of a wonderful dream linger tantalizingly at the edge of your consciousness, but as you try to grasp these fleeting threads of memory, they slip through your fingers like sand. 

The experience of forgetting one’s dreams is a common yet puzzling phenomenon. To understand this, let's delve into the realm of neuroscience and explore what goes on in our brains as we slumber.

When we sleep, we go through sleep cycles that consist of several stages, each characterized by distinct brain wave patterns and eye movements. These stages can be divided into two main categories: Rapid Eye Movement (REM) sleep and Non-REM (NREM) sleep. First comes NREM sleep, wherein brain wave patterns and eye movements are slow. This category includes stages N1, N2, and N3, during which your body performs essential tasks crucial for physical restoration and deep rest. Later on, REM sleep occurs. This is characterized by heightened brain activity levels, like when awake, and rapid eye movements. This is the stage when dreams most commonly occur.

During the REM stage, norepinephrine is deficient in the cerebral cortex, a region crucial for memory, thought, and consciousness. Studies suggest that norepinephrine enhances memory in humans, so a lack of this chemical messenger during the periods when we dream may contribute to our forgetting them. 

Recent research has also shown that dreaming is closely related to other forms of mental functioning that we experience while awake. These states of thinking can be organized into a spectrum. At one end of this spectrum are states of thinking that require concentration. These processes are associated with high activity levels in a specific brain region, the dorsolateral prefrontal cortex (dlPFC), which is involved in working memory. Think of answering a test, playing a sport, or acing a job interview.

On the other end of the spectrum are more spontaneous, imaginative thought processes, including mind wandering and dreaming. Unlike the other end of the spectrum, where thoughts require active engagement and conscious effort, these states of mind are more disorganized and may lack a clear direction or goal. 

We have thousands of thoughts each day but only remember a minuscule fraction by the end of the day. Try to recall what you were thinking about the last time you brushed your teeth. Chances are, you can’t. When we think without consciously directing our thoughts to a problem or task at hand, the dlPFC is not activated, so these thoughts are deemed irrelevant and not stored. 

Dreams work in the same way. The dlPFC is not activated because dreaming is categorized on the end of the spectrum associated with nonessential thoughts, so we do not usually retain these memories unless the dreams are remarkable enough to stimulate activity in the dlPFC. 

Unfortunately, while our dreams may seem incredibly interesting, they are nothing more than a result of our brains wandering about and piecing together random bits of memories. While we’d love to remember our dreams, our brains, unfortunately, have other plans as they successfully erase the whimsical plots our hearts wish so dearly to be able to recall.

Sources:

https://www.ncbi.nlm.nih.gov/books/NBK19956/

https://www.ncbi.nlm.nih.gov/books/NBK526132/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10091095/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3100422/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3495093/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7279884/

https://www.sciencedirect.com/topics/neuroscience/dorsolateral-prefrontal-cortex

https://www.scientificamerican.com/article/why-do-memories-of-vivid-dreams/