The author John Steinbeck said: "It is a common experience that a problem difficult at night is resolved in the morning after the committee of sleep has worked on it."

Many others have claimed they formulated breakthroughs and innovations in dreams. Recent studies on the science of sleep suggest these claims are supported by modern science.

A 204 study suggests that sleep can help us make more rational, informed decisions, and not be swayed by a misleading first impression. To show this, researchers at Duke University in the US had participants take part in a garage-sale game.

In the experiment, participants rummaged through virtual boxes of unwanted goods. Most items in the box weren't worth much, but a few special objects were more valuable. After searching through several boxes, participants were asked to pick their favourite box and would earn a cash reward equivalent to the value of the items in the box.

When participants had to decide on a box right away, they tended to judge the boxes not by their entire contents, but rather by the first few items. In other words, these participants were unduly influenced by the first information they encountered and didn't factor in later information into their decision.

When participants slept and made their decision the next day, they made more rational choices, and the position of the valuable items in the box did not seem to influence their decision.

Problem-solving in the sleeping brain

When we are stuck on a difficult problem, it can feel like we have reached an impasse. A 2019 study found that when they gave the sleeping brain cues, in the form of sounds tied to an unsolved problem, it seemed to help participants to solve that problem the next day.

In this experiment, participants were given a set of puzzles to solve. While solving the puzzle, a unique sound was played in the background. At the end of the testing session, researchers gathered all of the puzzles that participants were unable to solve. While the participants were asleep, the researchers played back sounds associated with some of the unsolved puzzles.

The next morning, the participants came back to the lab and tried to solve the puzzles that they failed to complete the night before. The solving rate was higher for puzzles that were cued during the night, suggesting that the sound cues triggered the sleeping brain into working on a solution for that puzzle.

One of the ways that sleep might help us solve problems is by discovering insights into the relationships between objects and events. A study published in 2023 tested this idea.

The researchers had participants learn associations between four different items (one animal, one location, one object and one food), related to an event the researchers described to them. Some of the associations were obvious pairings, for example, item A was directly paired with item B. Others were only indirectly linked to the rest of the event, for instance, item D was never directly paired with items A or C.

The research team found that after a night's sleep, participants were better able to uncover the indirect associations (they discovered the subtle link between item A and D), compared to staying awake. This suggests sleep gave the participants insight into the underlying event structure.

Dreaming your way to creativity

Thomas Edison, who helped invent the light bulb, often used daytime naps to help spur his creativity even though he claimed not to sleep more than four hours a night.

When Edison went for his daytime naps, he fell asleep with a ball in his hand.

As he fell asleep, his hand relaxed, and the ball fell to the ground. The noise of the ball hitting the floor startled Edison awake. He, and other famous thinkers including Salvador Dali, claimed that it was that transitional state, the moment between wake and sleep, that fuelled their creativity.

In 2021, French scientists put Edison's claim to the test. They had participants attempt to solve a maths problem. Unknown to the participants, the problem had a hidden rule that would allow them to solve the problem much faster.

After working on the problem, they had participants fall asleep like Edison did. Each participant held a cup in their hand that they would drop if they fell asleep.

After this delay, participants were re-tested on the maths problem. They found that those participants who drifted off into a light sleep were better able to discover the hidden rule, compared with participants who remained awake, or who entered into deeper stages of sleep while still holding the cup.

During this twilight period between wake and sleep, many of the participants reported hypnagogia, dream-like imagery that is common during sleep onset.

In 2023, a different set of researchers investigated whether the content of hypnagogia was at all related to the three creatives tasks centred on a tree theme that their participants performed right before going to sleep. For example, listing all the creative, alternative uses they could think of for a tree. They found that creative problem-solving was enhanced when the hypnagogic imagery involved trees, suggesting imagery helped them to solve the problem.

So it turns out that Edison was right, sleep onset really is a creative sweet spot, and sleeping on it works.