Hollywood takes advantage of our continuing fascination with dreams. A favorite scene in many movies is when the hero experiences a terrifying dream sequence and then suddenly wakes up from the nightmare in a cold sweat. In the blockbuster movie Inception, Leonardo DiCaprio plays a petty thief who steals intimate secrets from the most unlikely of all places, people’s dreams. With a new invention, he is able to enter people’s dreams and deceive them into giving up their financial secrets. Corporations spend millions of dollars protecting industrial secrets and patents. Billionaires jealously guard their wealth using elaborate codes. His job is to steal them. The plot quickly escalates as the characters enter dreams in which a person falls asleep and dreams again. So these criminals descend deeper and deeper into multiple layers of the subconscious.
But although dreams have always haunted and mystified us, only in the last decade or so have scientists been able to peel away the mysteries of dreams. In fact, scientists can now do something once considered impossible: they are able to take rough photographs and videotapes of dreams with MRI machines. One day, you may be able to view a video of the dream you had the previous night and gain insight into your own subconscious mind. With proper training, you might be able to consciously control the nature of your dreams. And perhaps, like DiCaprio’s character, with advanced technology you might even be able to enter someone else’s dream.
THE NATURE OF DREAMS
As mysterious as they are, dreams are not a superfluous luxury, the useless ruminations of the idle brain. Dreams, in fact, are essential for survival. Using brain scans, it is possible to show that certain animals exhibit dreamlike brain activity. If deprived of dreams, these animals would often die faster than they would by starvation, because such deprivation severely disrupts their metabolism. Unfortunately, science does not know exactly why this is the case.
Dreaming is an essential feature of our sleep cycle as well. We spend roughly two hours a night dreaming when we sleep, with each dream lasting five to twenty minutes. In fact, we spend about six years dreaming during an average lifetime.
Dreams are also universal across the human race. Looking across different cultures, scientists find common themes in dreams. Fifty thousand dreams were recorded over a forty-year time period by psychology professor Calvin Hall. He followed this up with one thousand dream reports from college students. Not surprisingly, he found that most people dreamed of the same things, such as personal experiences from the previous days or week. (However, animals apparently dream differently than we do. In the dolphin, for example, only one hemisphere at a time sleeps in order to prevent drowning, because they are air-breathing mammals, not fish. So if they dream, it is probably in only one hemisphere at a time.)
The brain, as we have seen, is not a digital computer, but rather a neural network of some sort that constantly rewires itself after learning new tasks. Scientists who work with neural networks noticed something interesting, though. Often these systems would become saturated after learning too much, and instead of processing more information they would enter a “dream” state, whereby random memories would sometimes drift and join together as the neural networks tried to digest all the new material. Dreams, then, might reflect “house cleaning,” in which the brain tries to organize its memories in a more coherent way. (If this is true, then possibly all neural networks, including all organisms that can learn, might enter a dream state in order to sort out their memories. So dreams probably serve a purpose. Some scientists have speculated that this might imply that robots that learn from experience might also eventually dream as well.)
Neurological studies seem to back up this conclusion. Studies have shown that retaining memories can be improved by getting sufficient sleep between the time of activity and a test. Neuroimaging shows that the areas of the brain that are activated during sleep are the same as those involved in learning a new task. Dreaming is perhaps useful in consolidating this new information.
Also, some dreams can incorporate events that happened a few hours earlier, just before sleep. But dreams mostly incorporate memories that are a few days old. For example, experiments have shown that if you put rose-colored glasses on a person, it takes a few days before the dreams become rose-colored as well.
BRAIN SCANS OF DREAMS
Brain scans are now unveiling some of the mystery of dreams. Normally EEG scans show that the brain is emitting steady electromagnetic waves while we are awake. However, as we gradually fall asleep, our EEG signals begin to change frequency. When we finally dream, waves of electrical energy emanate from the brain stem that surge upward, rising into the cortical areas of the brain, especially the visual cortex. This confirms that visual images are an important component of dreams. Finally, we enter a dream state, and our brain waves are typified by rapid eye movements (REM). (Since some mammals also enter REM sleep, we can infer that they might dream as well.)
While the visual areas of the brain are active, other areas involved with smell, taste, and touch are largely shut down. Almost all the images and sensations processed by the body are self-generated, originating from the electromagnetic vibrations from our brain stem, not from external stimuli. The body is largely isolated from the outside world. Also, when we dream, we are more or less paralyzed. (Perhaps this paralysis is to prevent us from physically acting out our dreams, which could be disastrous. About 6 percent of people suffer from “sleep paralysis” disorder, in which they wake up from a dream still paralyzed. Often these individuals wake up frightened and believing that there are creatures pinning down their chest, arms, and legs. There are paintings from the Victorian era of women waking up with a terrifying goblin sitting on their chest glaring down at them. Some psychologists believe that sleep paralysis could explain the origin of the alien abduction syndrome.)
The hippocampus is active when we dream, suggesting that dreams draw upon our storehouse of memories. The amygdala and anterior cingulate are also active, meaning that dreams can be highly emotional, often involving fear.
But more revealing are the areas of the brain that are shut down, including the dorsolateral prefrontal cortex (which is the command center of the brain), the orbitofrontal cortex (which can act like a censor or fact-checker), and the temporoparietal region (which processes sensory motor signals and spatial awareness).
When the dorsolateral prefrontal cortex is shut down, we can’t count on the rational, planning center of the brain. Instead, we drift aimlessly in our dreams, with the visual center giving us images without rational control. The orbitofrontal cortex, or the fact-checker, is also inactive. Hence dreams are allowed to blissfully evolve without any constraints from the laws of physics or common sense. And the temporoparietal lobe, which helps coordinate our sense of where we are located using signals from our eyes and inner ear, is also shut down, which may explain our out-of-body experiences while we dream.
As we have emphasized, human consciousness mainly represents the brain constantly creating models of the outside world and simulating them into the future. If so, then dreams represent an alternate way in which the future is simulated, one in which the laws of nature and social interactions are temporarily suspended.
HOW DO WE DREAM?
But that leaves open this question: What generates our dreams? One of the world’s authorities on dreams is Dr. Allan Hobson, a psychiatrist at Harvard Medical School. He has devoted decades of his life to unveiling the secrets of dreams. He claims that dreams, especially REM sleep, can be studied at the neurological level, and that dreams arise when the brain tries to make sense of the largely random signals emanating from the brain stem.
When I interviewed him, he told me that after many decades of cataloging dreams, he found five basic characteristics:
1. Intense emotions—this is due to the activation of the amygdala, causing emotions such as fear.
2. Illogical content—dreams can rapidly shift from one scene to another, in defiance of logic.
3. Apparent sensory impressions—dreams give
us false sensations that are internally generated.
4. Uncritical acceptance of dream events—we uncritically accept the illogical nature of the dream.
5. Difficulty in being remembered—dreams are soon forgotten, within minutes of waking up.
Dr. Hobson (with Dr. Robert McCarley) made history by proposing the first serious challenge to Freud’s theory of dreams, called the “activation synthesis theory.” In 1977, they proposed the idea that dreams originate from random neural firings in the brain stem, which travel up to the cortex, which then tries to make sense of these random signals.
The key to dreams lies in nodes found in the brain stem, the oldest part of the brain, which squirts out special chemicals, called adrenergics, that keep us alert. As we go to sleep, the brain stem activates another system, the cholinergic, which emits chemicals that put us in a dream state.
As we dream, cholinergic neurons in the brain stem begin to fire, setting off erratic pulses of electrical energy called PGO (pontine-geniculate-occipital) waves. These waves travel up the brain stem into the visual cortex, stimulating it to create dreams. Cells in the visual cortex begin to resonate hundreds of times per second in an irregular fashion, which is perhaps responsible for the sometimes incoherent nature of dreams.
This system also emits chemicals that decouple parts of the brain involved with reason and logic. The lack of checks coming from the prefrontal and orbitofrontal cortices, along with the brain becoming extremely sensitive to stray thoughts, may account for the bizarre, erratic nature of dreams.
Studies have shown that it is possible to enter the cholinergic state without sleep. Dr. Edgar Garcia-Rill of the University of Arkansas claims that meditation, worrying, or being placed in an isolation tank can induce this cholinergic state. Pilots and drivers facing the monotony of a blank windshield for many hours may also enter this state. In his research, he has found that schizophrenics have an unusually large number of cholinergic neurons in their brain stem, which may explain some of their hallucinations.
To make his studies more efficient, Dr. Allan Hobson had his subjects put on a special nightcap that can automatically record data during a dream. One sensor connected to the nightcap registers the movements of a person’s head (because head movements usually occur when dreams end). Another sensor measures movements of the eyelids (because REM sleep causes eyelids to move). When his subjects wake up, they immediately record what they dreamed about, and the information from the nightcap is fed into a computer.
In this way, Dr. Hobson has accumulated a vast amount of information about dreams. So what is the meaning of dreams? I asked him. He dismisses what he calls the “mystique of fortune-cookie dream interpretation.” He does not see any hidden message from the cosmos in dreams.
Instead, he believes that after the PGO waves surge from the brain stem into the cortical areas, the cortex is trying to make sense of these erratic signals and winds up creating a narrative out of them: a dream.
PHOTOGRAPHING A DREAM
In the past, most scientists avoided the study of dreams, since they are so subjective and have such a long historical association with mystics and psychics. But with MRI scans, dreams are now revealing their secrets. In fact, since the brain centers that control dreaming are nearly identical to the ones that control vision, it is therefore possible to photograph a dream. This pioneering work is being done in Kyoto, Japan, by scientists at the ATR Computational and Neuroscience Laboratories.
Subjects are first placed in an MRI machine and shown four hundred black-and-white images, each consisting of a set of dots within a ten-by-ten-pixel framework. One picture is flashed at a time, and the MRI records how the brain responds to each collection of pixels. As with other groups working in this field of BMI, the scientists eventually create an encyclopedia of images, with each image of pixels corresponding to a specific MRI pattern. Here the scientists are able to work backward, to correctly reconstruct self-generated images from MRI brain scans taken while the subject dreams.
ATR chief scientist Yukiyasu Kamitani says, “This technology can also be applied to senses other than vision. In the future, it may also be possible to read feelings and complicated emotional states.” In fact, any mental state of the brain might be imaged in this way, including dreams, as long as a one-to-one map can be made between a certain mental state and an MRI scan.
The Kyoto scientists have concentrated on analyzing still photographs generated by the mind. In Chapter 3, we encountered a similar approach pioneered by Dr. Jack Gallant, in which the voxels from 3-D MRI scans of the brain can be used to reconstruct the actual image seen by the eye with the help of a complex formula. A similar process has allowed Dr. Gallant and his team to create a crude video of a dream. When I visited the laboratory in Berkeley, I talked to a postdoctoral staff member, Dr. Shinji Nishimoto, who allowed me to watch the video of one of his dreams, one of the first ever done. I saw a series of faces flickering across the computer screen, meaning that the subject (in this case Dr. Nishimoto himself) was dreaming of people, rather than animals or objects. This was amazing. Unfortunately, the technology is not yet good enough to see the precise facial features of the people appearing in his dream, so the next step is to increase the number of pixels so that more complex images can be identified. Another advance will be to reproduce images in color rather than black and white.
I then asked Dr. Nishimoto the crucial question: How do you know the video is accurate? How do you know that the machine isn’t just making things up? He was a bit sheepish when he replied that this was a weak point in his research. Normally, you have only a few minutes after waking up to record a dream. After that, most dreams are lost in the fog of our consciousness, so it is not easy to verify the results.
Dr. Gallant told me that this research on videotaping dreams was still a work in progress, and that is why it’s not ready for publication. There is still a ways to go before we can watch a videotape of last night’s dream.
LUCID DREAMS
Scientists are also investigating a form of dreaming that was once thought to be a myth: lucid dreaming, or dreaming while you are conscious. This sounds like a contradiction in terms, but it has been verified in brain scans. In lucid dreaming, dreamers are aware that they are dreaming and can consciously control the direction of the dream. Although science has only recently begun to experiment with lucid dreaming, there are references to this phenomenon dating back centuries. In Buddhism, for example, there are books that refer to lucid dreamers and how to train yourself to become one. Over the centuries, several people in Europe have written detailed accounts of their lucid dreams.
Brain scans of lucid dreamers show that this phenomenon is real; during REM sleep, their dorsolateral prefrontal cortex, which is usually dormant when a normal person dreams, is active, indicating that the person is partially conscious while dreaming. In fact, the more lucid the dream, the more active the dorsolateral prefrontal cortex. Since the dorsolateral prefrontal cortex represents the conscious part of the brain, the dreamer must be aware while he or she is dreaming.
Dr. Hobson told me that anyone can learn to do lucid dreaming by practicing certain techniques. In particular, people who do lucid dreaming should keep a notebook of dreams. Before going to sleep, they should remind themselves that they will “wake up” in the middle of the dream and realize that they are moving in a dream world. It is important to have this frame of mind before hitting the pillow. Since the body is largely paralyzed during REM sleep, it is difficult for the dreaming person to send a signal to the outside world that he has entered a dream, but Dr. Stephen LaBerge at Stanford University has studied lucid dreamers (including himself) who can signal the outside world while dreaming.
In 2011, for the first time, scientists used MRI and EEG sensors to measure dream content and even make contact with a dreaming person. At the Max Planck Institute in Munich and Leipzig, scientists enlisted the help of lucid dreamers, who were fitted with EEG sensors on their heads to help the scientis
ts determine the moment they entered REM sleep; they were then placed in an MRI machine. Before falling asleep, the dreamers agreed to initiate a set of eye movements and breathing patterns when dreaming, like a Morse code. They were told that once they started dreaming, they should clench their right fist and then their left one for ten seconds. That was the signal that they were dreaming.
The scientists found that, once the subjects entered their dream state, the sensorimotor cortex of the brain (responsible for controlling motor actions like clenching your fists) was activated. The MRI scans could pick up that the fists were being clenched and which fist was being clenched first. Then, using another sensor (a near-infrared spectrometer) they were able to confirm that there was increased brain activity in the region that controls the planning of movements.
“Our dreams are therefore not a ‘sleep cinema’ in which we merely observe an event passively, but involve activity in the regions of the brain that are relevant to the dream content,” says Michael Czisch, a group leader at the Max Planck Institute.