The Science of Lucid Dreaming

When I was about 12, I had a dream that children I didn’t know were chasing me and my friends around the YMCA’s playground. Normally, this dream would have been commonplace, except for a strange moment. I had just run up the jungle gym and was about to slide down, away from my pursuer, when I turned back to him and asked, “Why are you even chasing me?” He stopped, stared back into my eyes, and answered “I dunno – this is your dream after all!” In that moment, I had a short-lived realization that none of this scenario was real.

Unfortunately, that thought was fleeting and I went back to running away from my imagined chaser for the remainder of the dream. Had I managed to hold onto the thought of “this isn’t real,” then I would have experienced what is called a lucid dream.

What is a lucid dream and how can I do it?

A lucid dream is when a person is asleep but realizes that they are in a dream. Often, they are able to control aspects of their dream world, and might gain the ability to fly or to meet a character that helps them solve a problem they’re facing in the real world. The level of control in a dream can vary wildly both between dreamers and across different dreams.

Lucid dreams can spontaneously occur in people who have never trained themselves to be lucid during sleep, but it’s very rare. Usually, sleepers who are interested in exploring lucid dreams must train themselves to recognize when they are in a dream. The most common way to do this is to practice what are called ‘reality checks.’ Because the sleeping brain constructs the dream environment and scenario, normal logic doesn’t apply, and dreamers can use this lack of normalcy to recognize when they are in the dream. One common reality check is to look at some written text, look away, and then look back. If the text changed between the two times you look at it, you know that isn’t something that would happen in the waking world. Well-practiced lucid dreamers use this technique and others similar to it across the day so that they’ll also remember out of habit to do the same technique when they are asleep. Although it’s an open question of research, it seems that most people can train themselves to have occasional lucid dreams.

How do we know that people who are lucid dreaming are actually asleep?

While lucid dreams might seem fun, if a bit weird, how can we tell that these people aren’t just awake and daydreaming? In order to scientifically study lucid dreams, we first need a good way to first measure sleep and then confirm that a person is lucid dreaming and not simply awake. This is where an old, but reliable method called electroencephalography comes into play.

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EEG Caps with Electrodes

Cognitive scientists use a science-fiction-looking cap that contains many electrodes to record brain activity from the scalp. While the equipment might look high-tech, the signal it collects is simply an amalgamation of electrical activity coming from vast numbers of neurons firing under the skull. Electroencephalography, more commonly called EEG, is the practice of recording the brain’s electrical signals from electrodes placed on the scalp. In essence, the cells in our brains (called neurons) communicate with each other using electrical signals. A single cell does not produce much voltage but when many neurons fire together, the combined strength of their signals can be read by an EEG cap even from outside the skull and skin that make up our scalp. Although EEG cannot discern what single neurons are saying to one another, the technique does allow researchers to identify times when lots of neurons synchronize their activity and work together on a particular task. Another added benefit is that EEG can record in fractions of a second, giving researchers a good idea of how very fast processes happen in the brain. So while cognitive scientists cannot ‘read your mind’ with EEG, they do take advantage of this cool research technique to uncover how things like attention, memory, and self-control work.

Using EEG, scientists can monitor a person’s brain as they drift off to sleep and move through the different stages of sleep. They can also use it to tell when someone has woken back up, based on the way his or her brain waves speed up in frequency and decrease in amplitude. Using this technique, researchers can watch the brain of a sleeping person and measure when they’ve reached REM sleep – the most common time to experience dreams.

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Me with an EEG cap on
How can we study lucid dreams?

Now that we’ve established a way to measure sleep, we’ll discuss how scientists use EEG to discern if someone is having a lucid dream. The key is to include electrodes placed near the eyes to measure eye movement as well as brain activity. The electrodes are placed horizontally beside and vertically below the eyes using small stickers so as not to make the participant uncomfortable. These electrodes are primarily used to measure the indications that someone has entered REM sleep, namely by recording the rapid eye movements that gives the sleep stage its name. However, they can serve a dual purpose by giving lucid dreamers a way to contact the waking world. Although our bodies are paralyzed during sleep (unless you have a sleep disorder like sleep walking), we still have volitional control over the movement of our eyes. This key feature gave researchers a way to peek into the world of lucid dreams by having the dreamers perform an easily recognizable eye movement task.

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EEG Data

Starting with researcher Keith Hearne in 1978, scientists asked lucid dreamers to rapidly move their eyes left-right-left whenever they recognized that they were in a lucid dream. The EEG signal their intentional eye movement produced clearly stood out from the usual small eye movements during regular REM periods. By cross-validating this technique with the practice of waking up lucid dreamers to ask them about their dreams, researchers have found intentional eye movements are an effective way for a dreamer to communicate that they are indeed experiencing a lucid dream, while still maintaining the usual REM brain signals to show they are still asleep.

This clever research technique has given us a chance to scientifically study the ephemeral world of lucid dreaming. Rather than relying on the Freudian practice of asking what a person dreamt about and what it ‘means,’ we can now start to test specific hypotheses about lucid dreaming. Perhaps in studying lucid dreams, we will gain a better understanding of the layers of consciousness between wake and deep sleep.

Sadie Witkowski is a sleep and memory researcher at Northwestern University, and host of the podcast PhDrinking. You can find her online as @SadieWit or at @PhDrinking for more on her science communication work.