Research shows ‘hot zone’ that’s active during dreaming
Neuroscientists from the Wisconsin Center for Sleep and Consciousness reported in Nature Neuroscience in April that they identified a “hot zone” in the back of the brain where high-frequency electrical activity shows when the brain is actively dreaming.
The study also showed both dreams and dreamless sleep occur in both Rapid Eye Movement (REM) sleep and non-REM sleep. Also, the contents of those dreams – whether they involved movement, faces or speech, for example – were tied to higher activity in the parts of the brain in charge of those actions during wakefulness.
Giulio Tononi, professor of psychiatry and the study’s senior author, says the study also shows that dreams may be a valuable model for studying consciousness.
“Dreams are forms of consciousness that occur during sleep. In the course of a night’s sleep, consciousness varies considerably: it can either be absent or present in the form of thoughts, images or dreams,’’ says Tononi, who directs the center.
“We were able to compare what changes in the brain when we are conscious (during dreaming) compared when we are unconscious, during the same behavioral state of sleep. In this way we could zoom in on the brain regions that truly matter for consciousness and avoid confounding factors having to do with being awake rather than asleep or anesthetized.”
A total of 46 volunteers slept at the laboratory wearing nets covered with 256 electrodes that covered their scalps and part of their faces. The electrodes created a high-density electroencephalography (HD-EEG) report of electrical activity in their brains. The sleepers were awakened by a tone, and asked to report whether they were dreaming.
The first experiment showed that in both REM and NREM sleep, sleepers reported dreams when the ‘posterior hot zone’ of their brains was activated. This suggests dreaming depends on this brain region being active, and not on the sleep stage.
In the second test, the sleepers reported the content of their dreams. Their brains showed high-frequency activity in regions associated during wake with the dreams’ contents. For example, dreams associated with hearing speech triggered activity in Wernicke’s areas on the left side of the cerebral cortex, which is involved in language perception and understanding.
“This suggests that dreams recruit the same brain regions as experiences in wakefulness for specific contents,” lead author Dr. Francesca Siclari says. “This also indicates that dreams are … not ‘inventions’ or ‘confabulations’ that we make up while we wake up.”
In the final experiment, researchers use could EEG readings to predict the presence of dreaming 92 percent of the time and the absence of dreaming 81 percent of the time.
“This is the first time someone has shown that absent or forgotten dream experiences also carry a distinct EEG signature, which should encourage us to take reports of dream experiences at face value,” Siclari says.