New Study Shows That You Can Solve Problems as You Sleep

“Let me sleep on it” may be a legitimate plan for problem-solving, according to a new study.

By Nicole Gleichmann

Do you ever wake up and suddenly have the answer to something that’s been replaying in your mind? It can feel as if your brain was working with no conscious effort as you slept soundly. Maybe your problem was analytical, having to do with a mathematical equation. Or perhaps it was more emotionally driven, such as deciding whether to take a new job.

The experience of working through something in our sleep is so common that we have a saying for it: “Let me sleep on it.” Just this month, researchers from Northwestern University have published findings that support the idea that we can solve problems during sleep.

woman hooked up for sleep study at night at sleep clinic

In the study published in Psychological Science, Kristin Sanders and her team used sounds and puzzles to study problem-solving during sleep.

57 participants were given puzzles during the evening, each of which was matched with a unique and arbitrary sound. That night when the participants slept, the same sounds were played for ½ of the puzzles that they did not solve. The idea was that the sound might cue the brain to think about that problem while sleeping.

The following morning, the participants were presented with the puzzles that they did not solve the prior evening. They solved an average of 31.7% of the puzzles for which the sound was cued during sleep, but only 20.5% of the puzzles for which no sound was played. This is a 55% improvement in problem-solving by playing the associated sound.

These findings suggest that we can work through cognitive challenges as we slumber away in our warm, comfy beds.

Memory and Sleep

What led to the researchers’ curiosity about problem-solving during sleep? It all has to do with the relationship between memory and sleep.

One of the most well-understood benefits of sleep has to do with memory. As we sleep, our brains are busy working on memory consolidation. This process involves strengthening memories, pruning memories that are no longer needed, and organizing them in a way that allows us to recall them at a later date.

The team hypothesized that humans might be capable of problem-solving during sleep because solving problems involves similar cognitive steps as storing memory. To solve a problem, one must take a variety of knowns and restructure them until a solution is determined, similarly to how memories are reorganized during slumber.

Their study provides evidence that we do work through scenarios and problems as we sleep. These results give us even more reason to get the recommended amount of sleep each night.

Sleep and the Brain

It can be tempting to think of sleep as a period of calm. This idea is so ingrained in our culture that “rest” is another term for sleep. However, this study and previous research on the brain and sleep demonstrate that our minds are incredibly active as we sleep.

Scientists are still elucidating the exact role of sleep on brain health and cognition. What we do know is that there are times during sleep when our brains are just as active as when we are awake. And when we don’t get enough sleep, our mental health and cognitive abilities suffer.

Our brains cycle through distinct stages as we lie in bed. These stages are:

  • Stage 1 Sleep: This is the lightest stage of sleep where our brains are transitioning from a waking to a sleeping state. Brain waves begin to slow, and we are easily woken up.
  • Stage 2 Sleep: Stage 2 sleep is the other stage of light sleep. Brain waves slow further as the brain prepares for deep sleep.
  • Stage 3 Sleep: Also known as deep sleep or slow-wave sleep, stage 3 sleep is vital for the rejuvenating benefits of sleep. The more deep sleep you get, the more likely you are to wake up feeling well-rested and ready for the day. It is difficult to wake someone up during deep sleep.
  • REM Sleep: Rapid eye movement sleep, or REM sleep, is the stage of sleep where most of our dreams occur. It is believed that dreaming plays a role in memory storage and consolidation. This is also likely the stage where problem-solving occurs. During this sleep stage, our brains are as active as they are when we are awake.

It takes our brains roughly 90 minutes to complete a full sleep cycle, at the end of which the cycle will start over. Each night, you should aim to get between 4 and 6 complete sleep cycles, or around 6 to 9 hours of sleep. 7 hours of sleep pops up time and again as the optimal duration of sleep for mental and physical health.

When we do not get enough sleep, more than our energy levels suffer. Insufficient sleep is tied to memory problems, mood disorders, and weight gain, amongst many other harmful effects. Plus, you might just come up with a solution to a problem as you catch your Z’s.


We now know that it is possible to solve problems as we slumber away at night. You can use this knowledge to your advantage by thinking about issues you’d like to address shortly before going to bed at night. A brief journaling session can allow you to work through your current struggles, leaving anything unsolved fresh on your mind for your bedtime problem-solving. Just be sure to get the recommended 7 to 8 hours of sleep each night.

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