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The Sciences

Ask Discover: Why Don't We Know When We're Dreaming?


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Got a burning science question? Send it to and we’ll try to answer it here or in a future issue of the magazine.


The print version of Discover Magazine has a new feature called Ask Discover, where readers’ questions are answered by one of the bloggers. In the current issue, Alan Schertzer asked:

Why don’t we know when we’re dreaming, especially when we interact with dead characters? My dad died a long time ago, yet when he inhabits my dreams, it seems perfectly normal. Do we all become morons when dreaming?

You can find my brief answer in the printed magazine, but here’s a slightly longer take.

This is a very good question. Dreams are, literally, an everyday experience but they are, when you think about it, extremely puzzling things. The topic of dreams touches on some of the deepest problems in neuroscience: the self, memory, and self-awareness. Even the question of why dreams happen is hotly debated.

In dreams, we often have bizarre experiences that seem perfectly normal at the time. We do not realize that what’s going on is impossible. This may be because in dreams we rarely reflect on our own experiences, thoughts, or self.

However, occasionally, people do become aware that they are in a dream: this is called lucid dreaming. It happens to many people from time to time (I can recall four or five lucid dreams, myself, mostly in childhood). With training, some people are able to achieve lucidity more often.

The essence of a lucid dream is self-awareness. So lucidity could offer neuroscientists a window onto the nature of dream unawareness.

In normal dreams, some areas of the brain are less active than when we’re awake. In particular, activity in the precuneus, part of the medial parietal lobe, is lower.

The precuneus is activated during selfreflective experience as well as being a hub of the ‘default mode network‘. This is a set of brain areas that’s active ‘by default’ when we’re awake – although it’s deactivated whenever we’re engaged in an external activity or task that demands attention.

In one small study, activity in the precuneus was higher during lucid dreamsthan in normal ones. So the precuneus, and connected areas, might be responsible for the insight that’s often lacking in dreams. An analogy might be that dreams are like a dramatic, attention-grabbing external event that leaves us ‘no time to think’ about ourselves or what it means.

But how this actually happens is unknown. There is evidence that somethingin the precuneus is at work, but we don’t yet know how the millions of neurons in this area can give us waking self-awareness, or how dreams switch this off.

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