We dream all the time, but we can’t always recall the nightly visions. Why are some dreams more memorable than others?
Throughout each night, you pass through different sleep stages. During the first half of the night, deep sleep prevails, during the second – REM. Though we dream in all sleep stages, most dreams occur in REM – and thus, in the early morning hours. So, the time of the dream is the first factor in remembering it.
We most often remember dreams immediately upon waking up, when the images are still fresh in our memory. It happens because basically the whole brain is involved in the act of dreaming. If you put a dreamer inside an MRI, you’d see how the cortex areas are lit up. The hippocampus and the amygdala (responsible respectively for memory and emotions) light up 30% more when we dream, and so does the visual cortex. So, when you wake up from REM sleep, there’s a high chance you’ll still have the afterimages in your head, and it’s very likely you will remember the dream.
But that’s not all. REM sleep has many purposes and dealing with emotions is one of them. Remember how the amygdala – the emotional steering wheel – lights up 30% more in REM than when you’re awake? That’s partially because, during REM, our memories get “de-emotionalized” – the emotional charge is removed. Since emotions are processed in REM, they are sometimes woven into the content of our dreams. The more emotional the dream, the more it sticks in your memory.
Take nightmares for example – dreams with quite an emotional charge that you often remember very vividly. The feelings of fear we experience in a nightmare are so intense that they remain even after you wake up in terror. These lingering emotions ensure that we will remember this dream, although this is a category we would like to forget altogether.