PRESENTER: In a well-known 1957 study, two experimental psychologists-- William Dement and Nathanial Kleitman-- argued that REM corresponds to dreaming.

Since that time, there have been numerous studies. For example, today, Dr. Nir at Tel Aviv University, has come very close to proving that REM corresponds with eye movement by monitoring the sleep of volunteers with epilepsy. These volunteers had electrodes implanted deep into their brains to help with treatment. Reports in the New Scientist journal.

Nir and his colleagues found that activity seemed to spike about quarter of a second after a flicker, just as it would when seeing an image when you're awake. Dr. Nir reports that he and his research team are sure that the brain is alternating between different imagery.