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Hardly Remembered Dreams

We often remember nothing of our dreams, but we remember that we did dream. Why?

Key points

  • Dreams of this kind are called "contentless" or "white" dreams.
  • Dreams and remembering use similar mental capacities.
  • We can now reconstruct dreamed objects and scenes just from the activation of the early cortical regions.

We often remember our dreams. But not always. According to recent statistics, 45 percent of dreams are remembered, whereas, in 22 percent of cases, there is no memory of any dream whatsoever. But how about the remaining 33 percent? In these cases, we remember that we had a dream, but remember absolutely nothing about the content of this dream. This is a very odd feeling. You wake up. You know you had a dream. But no matter how hard you try, there is absolutely nothing you can remember about what you dreamed.

"Contentless" or "White" Dreams

Dreams of this kind are called "contentless" or "white" dreams: "contentless" because you remember that you had a dream, but you don't remember the content of the dream, and "white" because, in some sense, when you remember, you draw a blank. One of the most exciting questions in dream research is about why we can't remember white dreams.

There are two main options. The first option is that the lack of any memory of the content of these dreams may be a shortcoming of our memory. So the dreams, when we had them, were as vivid as the dreams we do remember, but, for some reason, we just lost access to them. In some very real sense, they are lost dreams.

The second option is that these dreams are, to begin with, lower quality in signal. So they are not as vivid as the dreams we do remember. They are more like a grainy TV screen with muffled sound. So the reason we don't remember what they are about is not a shortcoming of our memory, but rather of the original dream content. The dreams are not lost because they were never really there.

Two Uses of Mental Imagery

What makes this question especially tricky is that dreams and remembering use very similar mental capacities. Dreams have long been considered to be a form of mental imagery: perceptual states that are not triggered directly by the sensory input, after all, there is no sensory input—your eyes are closed. But the very act of remembering also heavily relies on mental imagery as we have plenty of evidence that episodic memory itself is a form of mental imagery. Episodic memory involves early perceptual processing, which is certainly not directly triggered by sensory input. One empirical reason for this is that the loss of the capacity to form mental imagery results in the loss (or loss of scope) of episodic memory. An even more important set of findings is that relevant sensory cortical areas are reactivated when we recall an experience.

So when we remember our dreams, we have mental imagery (the episodic memory) about mental imagery (our dream). Which of these two very different uses of mental imagery goes wrong when we have white dreams?

We can make progress on this question because we can now reconstruct dreamed objects and scenes just from the activation of the early cortical regions. So if I put you in an fMRI scanner and you fall asleep, I can tell not only whether you are dreaming, but also the outlines of your dream images.

Dreams are often thought to be the final frontier of fully private experiences—something we and only we know about. It turns out that this is not so. The experimenter may know your dreams better than you do. And this could include your forgotten dreams.