Many of us read before we go to bed. This activity is helpful in allowing our minds to relax and cue our bodies that it’s time to sleep. But, have you ever noticed that sometimes you forget what you have read just before falling sleep? When you pick up your book the next day, does it seem like you put your bookmark on the wrong page, because it’s like you never read those pages at all?
If you’re not a reader, maybe you’ve noticed that you forget what you talk about or think about in the moments leading up to sleep? Or even more mysterious, have you ever wondered why you never remember the exact moment you fall asleep?
Well, you are not alone. This phenomenon happens to many people and is considered a form of “amnesia” that occurs as a result of our brain switching from wakefulness to sleep.
The parts of the brain involved in forming and keeping new memories do some interesting things when we sleep. First, our level of attention (hopefully) starts to diminish in the moments before drifting off to sleep. We become less aware of our surroundings and less responsive to outside noise. Therefore, we may not “encode” new memories very well during these moments before sleep because we are simply not paying enough attention. The brain does not like it when the attention process works too hard before falling sleep. In fact, if you try to pay attention too much before sleep (e.g. obsessively worry about not sleeping), chances are, you won’t fall asleep! The brain needs to power down these processes in order to switch from wakefulness to sleep.
In addition to the encoding phase of memory, new memories need to be transferred from short-term storage to long-term storage, in order for memories to stick around longer than a few minutes. This process is called consolidation. Sleep studies have shown that when someone is presented with new information (like a list words) in the moments leading up to sleep, it is very difficult to remember these words upon waking. Interestingly, sleeping for only a few seconds (less than a minute) does not seem to affect the brain’s ability to learn and recall new information. However, after only ten minutes of sleep, recalling words from the list is very difficult.
It’s not completely clear, but it seems that the process of falling asleep closes a gate, in a sense, to the consolidation process. New memories can’t be transferred from short-term to long-term storage when this gate is closed. Therefore, no matter how hard you try, you can’t remember those lost moments right before sleep because they were never consolidated into long-term memory storage!
It’s important to note; however, that sleep is extraordinarily important for memory. Without healthy sleep, memory is deeply affected. Individuals with insomnia or obstructive sleep apnea often report memory problems throughout the day. Other than those elusive few minutes right before falling asleep, the act of sleep itself is necessary for proper consolidation of new learning. That’s why pulling an all-nighter before final exams is never a good idea!
To sum up, a good night’s sleep is crucial to our mental and physical health. Without a good night’s sleep, we can’t concentrate or remember things as well as we should. However, in the moments leading up to sleep, our brain starts to power-down its ability to form new memories. So don’t bother struggling to read one more page of that book before falling asleep—chances are, you will need to re-read it tomorrow!
