Inception-style lucid dreams can be induced by applying a specific frequency of electric current to sleepers' brains, a study has found.
Lucid dreams involve a state of heightened awareness that allows the sleeper to recognise the dream and control what happens within it.
A similar concept was explored in the hit movie Inception, starring Leonardo DiCaprio.
People who have lucid dreams talk of "waking up" within a dream and being able, for instance, to fly at will or manipulate the imaginary world around them.
In the new study, researchers tested 27 participants with no previous experience of lucid dreaming over several nights.
After three minutes of uninterrupted Rapid Eye Movement (REM) sleep - the sleep phase when most dreaming occurs - a weak alternating electric current was applied to their scalps.
The scientists targeted the frontal and temporal brain regions where high-frequency "gamma" brainwaves had previously been associated with lucid dreaming.
A few seconds after the brain stimulation the volunteers were awakened and reported having lucid dreams.
Stimulation at a frequency of 40 hertz both raised gamma activity and induced lucid dreaming. It also correlated with specific aspects of lucid dreams, such as insight - realising you are dreaming - control over the dream plot, and dissociation from the dream's protagonist.
Writing in the journal Nature Neuroscience, the team led by Dr Ursula Voss, from the JW Goethe-University in Frankfurt, Germany, speculated on the use of lucid dreams to help victims of post-traumatic stress disorder who are plagued by nightmares.
"Promoting gamma oscillations during REM sleep in post-traumatic stress disorder with re-emerging nightmares might trigger lucid dreaming and eventually enable active changes in dream content," said the researchers.