Like islands sticking out from the smooth surface of the ocean, dreams pierce our sleep with incoherent episodes of consciousness. Where these scraps of thoughts appear in a sleeping brain - this question has long troubled scientists and philosophers. For decades, scientists have associated dreams with Rapid Eye Movement (REM), when the resting brain paradoxically produces high-frequency brain waves that are very similar to those born during wakefulness.
And yet we see dreams not only during REM. Several bizarre studies have found signs of dreaming during non-REM sleep, when slow-wave activity reigns in the brain - the opposite of an anxious, active, conscious state. And so, thanks to research that was published in Nature Neurosciece, we seem to have begun to grope for an answer to a wicked dilemma.
By carefully monitoring the brain waves of the sleeping volunteers, a team of scientists from the University of Wisconsin pinpointed a local "hot spot" in the brain that is activated when we sleep, regardless of the sleep phase the person is in.
"You can actually identify the signature of the sleeping brain," says study author Dr. Francesca Siclari.
Moreover, using an algorithm developed on the basis of her observations, a group of scientists was able to accurately predict when a person sleeps, with 90% accuracy, and more …
… and here is the most interesting …
… to roughly disassemble the content of dreams.
“We found that the sleeping brain and the waking brain can be much more similar than imagined,” Siclari says.
Promotional video:
This research not only opens the door to dream modeling for PTSD therapy, but it may help scientists find a clue to the mystery of consciousness.
"The importance of this article is astounding," says Dr. Mark Blagrov of Swansea University in Wales, who was not involved in the study.
Sleep Anatomy
During a full night sleep cycle, we go through various stages characterized by distinctive brain patterns. Scientists often use EEGs to accurately capture each stage of sleep, which involves placing 256 electrodes on a person's skull and then tracking the number and size of brain waves at different frequencies.
When we doze off, our brains exhibit low-frequency activity that travels across the entire surface. These waves signal that neurons are in a “quiescent state” and are unable to communicate between areas of the brain - therefore, low-frequency activity is often associated with loss of consciousness.
These slow fluctuations in non-REM sleep eventually translate into high-frequency activity, signaling the transition to rapid eye movement. This sleep phase is often associated with vivid dreams - and this connection is so deeply rooted in sleep research that instances of dreamless RHD or non-REM sleep have often been ignored as oddities.
It turns out that these strange cases hinted to us that our current understanding of the neurobiology of sleep is incomplete.
Dream catchers
To reconsider these paradoxical results, Siclari and her team monitored the brain activity of 32 volunteers using EEG and woke them up overnight at random intervals. The scientists then asked the sleepy participants if they dreamed of something, and if so, what exactly they dreamed. In total, this happened 200 times per night.
But instead of seeing a global shift in activity associated with sleep, scientists were surprised to find an area of the brain in the back of the head that was dynamically shifting its activity based on emerging dreams.
Dreams were associated with a decrease in low-frequency waves in the "hot zone" and with an increase in high-frequency waves, reflecting high rates of neural activations and brain activity. It was a kind of awakening, independent of sleep stage or general brain activity.
“All indications are that very limited, well-defined brain activation is needed to generate conscious experience,” Siclari says. "Until now, we thought that large areas of the brain must be activated to generate conscious experiences."
It makes sense that the hot zone connects to the action during sleep. Previous work has shown that stimulating these areas of the brain with an electrode can create a feeling of being "in a parallel world." This hot zone also contains areas that integrate sensory information to build a virtual model of the world around us. This kind of simulation lays the foundation for many of our imaginary worlds, and this hot zone is well suited for this,”the authors say.
If an active hot zone is in fact a “sleep signature,” its activity should be able to tell if a person is asleep at a given moment. The authors created an algorithm based on their results and tested its accuracy on a separate group of people.
“We woke them up whenever the algorithm told us they were asleep, 84 times in total,” the researchers write.
In total, this algorithm showed 90 percent accuracy in analyzing the presence of sleep - even in cases where the participants did not remember the contents of their dreams, but were sure that they were asleep.
Reading dreams
Since the hot zone contains areas that process visual information, the scientists wondered if it was possible to access the contents of the subjects' dreams using EEG readings.
Dreams can be extremely tangible, with unfolding events, or completely abstract, like free fantasy, scientists say. Faces, places, movements and speech are all familiar components of dreams that are processed by easily identifiable regions of the hot zone, so the researchers decided to focus on these aspects.
Remarkably, the volunteers who reported what they said in their dreams exhibited activity in the areas of the brain responsible for speech; and those who dreamed of people showed activity in face recognition centers.
“This suggests that dreams use all of the same brain areas as conscious experiences during waking for certain content,” Siclari says, noting that earlier research could only show this in the “twilight zone,” the transition between sleep and wakefulness.
Finally, scientists are interested in what happens when we sleep, but do not remember the specific details. It turned out that this strange state has a separate EEG signature: memorizing sleep details was associated with a burst of high-frequency activity in the anterior regions of the brain.
Interesting questions arise, for example, are the frontal lobes of the brain responsible for lucid dreaming, a special state when people understand that they are sleeping and can change the contents of sleep.
Awakening life
Scientists cannot yet explain what activates the hot zone during sleep, but the answers can tell us if sleep has a biological purpose, for example, processing memories into large concepts of the world.
Mapping the activity of the sleeping brain may also lead to ways to directly manipulate our dreams using non-invasive procedures such as transcranial stimulation. Sleep induction can help people with insomnia, and disrupting disturbed sleep can help PTSD patients get better sleep.
Dr. Giulo Tononi, lead author of the study, believes that the implications of this study go far beyond sleep.
“We were able to compare how the sleeping brain behaves versus the waking one. This research can be a valuable model for the study of consciousness,”he says.
ILYA KHEL