According to a new study, that's the frequency of electric current that, when sent to the frontal cortex via electrodes, best induced sleeping test subjects to become aware of their dream state. (Lower and higher frequencies had little effect.)
Researchers applied electrodes to the scalps of 72 test subjects and, once they fell asleep and entered a dream state — as indicated by brain activity — zapped them with 30-second bolts of electric current with frequencies ranging from two to 100 hertz (Hz). They then woke the subjects and asked them to describe their dreams. Seventy-seven percent of those who received a hit of 40 Hz reported being aware of their dream state while sleeping, a phenomenon commonly known as lucid dreaming.
What’s the Big Idea?
Lucid dreaming corresponds with gamma wave activity in the brain’s frontal cortex. Normally, this type of activity isn’t present during sleep. However, not only did it increase as a result of the electrical stimulation, subsequent lucid dreams without stimulation showed an even greater increase. Researcher Ursula Voss of J.W. Goethe-University Frankfurt says, “We were surprised that it’s possible to force the brain to take on a frequency from the outside, and for the brain to actually vibrate in that frequency and actually show an effect.” Details of the study appear in Nature Neuroscience.
Partially in response to recent research into adolescent sleep patterns, one English school has announced that sixth-form classes — attended by students aged 16-18 — will start at 1:30 PM and end at 7:00 PM.