Lucid dreaming is when a sleeper recognises they are dreaming and may even be able to manipulate the dream's plot and control their behaviour. The applied stimulation had a variety of frequencies between two and 100Hz, but neither the experimenter nor the volunteer was informed which frequency was used, or whether a current was applied. "Lucid dreaming is a very good tool to observe what happens in the brain and what is causally necessary for secondary consciousness," Voss said. By examining the sleepers' brainwaves over a range of frequencies, scientists have found that lucid dreamers demonstrate a shift towards a more "awake-like" state in the frontal and temporal parts of the brain, with the peak in increased activity occurring around 40Hz. In the study, the researchers placed electrodes on the scalps of 27 participants, who were not lucid dreamers, to stimulate the frontal cortex, and recreate the gamma wave activity that has been seen in lucid dreamers. The EEG data showed that the brain's gamma activity increased during stimulation with 40 Hz, and to a lesser degree during stimulation with 25 Hz; stimulation with other frequencies didn't lead to any changes in the brain waves, and it didn't increase the likelihood of people having lucid dreams. The researchers also found that after stimulation, if people did experience a lucid dream, the gamma activity increased even more. Hobson said the study could have implications in psychiatric research.
– Scientists may have found a way to cause lucid dreams—those experiences in which we know we're dreaming and can, in some cases, control the dream. The key, explains an expert, is electric scalp stimulation. "I never thought this would work," Harvard researcher Dr. John Allan Hobson tells LiveScience. "But it looks like it does." Researchers already knew that lucid dreamers exhibit a boost in brain activity in the frontal and temporal lobes comparable to being awake. In a study, they applied a variety of currents to the scalps of volunteers in REM sleep. Stimulation at certain frequencies—specifically, 40 Hz and 25 Hz—prompted increased activity in the frontal and temporal lobes, the Guardian reports. Some 77% of participants stimulated with 40-Hz currents reported lucid dreams. The study offers "a step in the direction of understanding how the brain manages to hallucinate and be deluded," says a researcher. It could also be beneficial in treating nightmares, the team says.