We've all heard the best approach to solve a problem is to "sleep on it." It turns out there may be more truth to this adage than previously thought. While stories abound of eureka moments surfacing from dreams, scientific evidence has remained elusive, due to the challenge of systematically manipulating dreams.

A new study by neuroscientists at Northwestern University validates the possibility of influencing dreams and offers a crucial step to support the theory that dreams in REM sleep--the rapid eye movement phase of sleep in which lucid dreaming can occur--may be especially conducive to helping individuals come up with creative solutions to a problem.

The study has been published in the journal Neuroscience of Consciousness.

By presenting sounds during sleep that reminded study participants of a prior experience of trying to solve a specific puzzle, a method known as targeted memory reactivation (TMR), the scientists were able to encourage participants to have more dreams about randomly selected unsolved puzzles. Importantly, experimenters presented sounds only with concurrent electrophysiological verification that participants were asleep.

They found that 75% of their participants experienced dreams that included fragments or ideas from the unsolved puzzles. Further, puzzles incorporated into dreams were solved more often than puzzles that were not (42% vs. 17%).

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