The veil over dreams and sleep first lifted a bit 50 years ago.

Illustration by Stacy Innerst, Post-Gazette Today is the second installment of a five-part series on the mysteries and meanings of dreams. The series will feature dream excerpts from local residents, as well as stories on the history of dream research; nightmares and how to confront them, strange sleep disorders that include people who walk, fight and eat while dreaming; and the controversial topic of lucid dreaming -- being able to know you're in a dream and partially control it. Click illustration for larger image. In Your Dreams Dream Journal: Tara Deringor Dream society seeks middle ground behind hard science and symbolism Experts trying to awaken Pittsburgh interest in dream study Yesterday The science of dreams Dreams: From falling to failing, it's the same old stories The 12 universal dreams Dreams and the arts: PG critics pick their dream theme team Insight from a decade-long journal of dreams A dream journal 'how-to'

That's when a University of Chicago graduate student, Eugene Aserinsky, played a hunch and used an old brain-wave machine to record the eye movements of his sleeping 8-year-old son.

Aserinsky, who worked with Dr. Nathaniel Kleitman, a pioneering sleep researcher, found that the brain doesn't simply slip into stupor at night. Instead, beginning 90 minutes after sleep's onset, a night's rest is regularly punctuated by periods of intense mental activity during which unseeing eyes jerk around under their lids.

This rapid eye movement, or REM, sleep proved to be a brain state distinct both from waking and from so-called slow-wave sleep, the quiescent state now known as non-REM sleep. During REM sleep, the middle ear also moves and men experience erections, though most of the body is paralyzed.

The idea that something more than rest was occurring during sleep was revolutionary. It sparked the creation of an entirely new medical specialty, sleep medicine, and energized a generation of researchers to take a closer look at dreaming.

A link between REM and dreaming was suspected from the outset, and within two years it was confirmed by another of Kleitman's young associates, Dr. William Dement, now director of the Stanford University sleep disorders clinic. Test subjects who were awakened during REM periods almost always reported that they had been dreaming and that the dreams often were vivid, bizarre and especially "dreamlike."

"It's hard to convey today the excitement we had then," William Domhoff of the University of California, Santa Cruz, recalled earlier this year at the annual meeting of the Associated Professional Sleep Societies in Chicago.

REM sleep had become synonymous with "dream sleep," he explained, and that made it easier for researchers to explore dreams by awakening subjects during REM episodes so they could immediately recount their nocturnal adventures. Researchers learned that the first REM period lasted about 10 minutes and, with each 90-minute sleep cycle, the REM period got longer, eventually taking up 20 to 25 percent of total sleep time.

Until Aserinsky's discovery of REM in 1953, most people had either dismissed dreams as meaningless or had embraced Sigmund Freud's theory that dream imagery was highly symbolic.

Freud contended that dreams are the mind's attempt to fulfill wishes that normally are repressed and that these wishes are so sexual or aggressive in nature that they would upset and waken the dreamer if not disguised in some way. Dreams are highly symbolic, he contended, because they must serve as "keepers of sleep," a mechanism to prevent people from waking prematurely.

Freud's views, expressed in his 1900 masterwork, "The Interpretation of Dreams," were so influential that some of the first experiments after the discovery of REM sleep tested his theory that a lack of dream sleep could cause schizophrenia. Subjects would be awakened at the onset of each REM episode throughout the night. But no one went crazy. Rather, they simply had longer REM periods during subsequent sleep periods.

By the early 1970s, evidence also was mounting that dreaming was not limited to REM periods. People often recall dreams shortly after falling asleep, a period of non-REM sleep.

The nature of dreams seems to vary depending on when they occur, said Dr. Daniel Buysse, medical director of the University of Pittsburgh Sleep Evaluation Center. Non-REM dreams, he noted, seem to be more rational and the images are more static. REM dreams, by contrast, are emotion-packed and usually filled with movement, complex plots and sometimes bizarre content.

Just random brainwaves?

If the early experiments disproved some of Freud's theories, a pair of psychiatrists at Harvard University, J. Allan Hobson and Robert McCarley, almost put Freud on the scrap heap in 1977 -- and some argue nearly killed dream research -- when they developed an explanation for dreams based on physiology, not psychology.

Click image to view a pdf-format graphic on the history of dreaming.

Using microelectrodes to record the activity of individual brain cells in cats, they determined that REM sleep and dreams were triggered by cells within a primitive area of the brainstem known as the pons.

REM is caused by the ebb and flow of various brain chemicals, called neurotransmitters, they suggested, and dreams are just the brain's best attempt to make sense out of the resulting flood of random signals. Dreams, as envisioned by Hobson and McCarley, might not be meaningless, but it was hard to see how they would have much deep meaning.

That doesn't mean that humans don't instinctively look for meaning in them.

"It's very difficult not to interpret them," Hobson said at this summer's sleep societies meeting, where he moderated a session on REM and dreaming. "We are symbol-decoding creatures."

Hobson's and McCarley's work was beautifully done, an exquisite explanation for how REM is turned on and off, acknowledged Rosalind Cartwright, a noted sleep disorders researcher at Rush University Medical Center in Chicago.

But it not only undercut Freud and psychoanalysis -- it suggested that dreams weren't of much consequence, period. And that caused many researchers to switch to other lines of inquiry, either because of growing disinterest or because their funding sources dried up.

"We mapped the geography of the night," Cartwright said, "and then we didn't know what to do with it."

But that began to change 10 years ago, when the technology for studying dreams made a quantum leap.

From the time of Aserinsky's first experiments, the only tool to study dreams had been brain wave monitoring -- electroencephalography. These electrical signals on the brain's surface could give researchers an idea of overall brain activity, but not of what was going on in specific structures within the brain.

But the advent in the 1990s of neuroimaging technology, such as positron emission tomography, or PET, and functional magnetic resonance imaging, or fMRI, made it possible to see which parts of the brain were active by monitoring how rapidly cells consumed glucose or the rate at which blood was flowing to different brain regions.

"For the first time, we would be able to look not at surface EEG structures but to go deep into the brain," said Dr. Eric Nofzinger, a Pitt psychiatrist.

In the mid-1990s, Nofzinger, who was intrigued by the similarities between the disturbed thinking of schizophrenic patients and the imagery of dreams, began to use Pitt's PET scanner to study sleeping subjects. In Belgium, Dr. Pierre Maquet pursued similar studies, as did Allen Braun at the National Institute on Deafness and Other Communication Disorders.

Emotional excitement

What they all found was that REM sleep activates the limbic system, a ring-shaped area deep within a primitive part of the brain. The limbic system is responsible for instinctual drives, sleep-wake regulation and, notably, emotions. Sensations such as sight and smell are influenced by the limbic system, along with the formation of memories. The limbic system includes the amygdala, an almond-shaped structure involved in generating fear and anxiety in response to stress and threats.

At the same time, the prefrontal cortex -- the brain's executive center that is responsible for higher reasoning, interpretation of stimuli and decision-making -- is shut down during REM sleep.

"It was really magical the first time we saw these things," Nofzinger recalled. This pattern of activation, he explained, was consistent with the characteristics of dreaming.

For instance, the active limbic system would explain why REM dreams are so emotionally charged and the amygdala in particular helps explain why the emotional content of dreams is so often negative -- dreams of fleeing from a dangerous animal or person, or dreams of being unprepared for a test.

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Meanwhile, the shutdown of the brain's rational prefrontal cortex helped explain why dreams often are nonsensical and have distorted time sequences. Because that part of the brain is also crucial for forming short-term memories, its deactivation no doubt contributes to people's difficulty in remembering their dreams.

This patchwork of active and inactive brain regions may be the reason many people recall dreams that feature somebody they know who, for some reason, looks nothing like that individual in real life. Belgium's Maquet and Sophie Schwartz of University College London say this is because facial identification requires several areas of the brain to work together, including the prefrontal cortex.

Likewise, people may dream that they can't find a building they are supposed to enter, or they can't remember information they need for a test. "But that may be because of your state," Buysse said. "Those parts of the brain are off-line. Your brain is kind of doing the best it can with half of it being asleep," he added.

Meanwhile, the brain's motor centers are active during REM, explaining why motion is so prevalent in dreams. But a switch in the brain stem disconnects the motor centers from the body, so the muscles are paralyzed, preventing people in most cases from acting out their dreams.

Though neuroimaging in the 1990s continued to challenge Freud's assumptions -- how could the brain be censoring itself if the rational prefrontal cortex was turned off? -- it also suggested that a deliberate process, not chaotic firing of neurons, was taking place during REM sleep.

"At least it's not random firing throughout the brain," Nofzinger said. In fact, the pattern of firing during REM sleep is very reliable. "It gives some assurance that there's some method to the madness of dreaming.

"I think you're still left with having to look at the psychological content of dreams."

Though Hobson still maintains that, "as scientists, we should give up on interpretation, at least for now," he acknowledges that the neuroimaging studies have changed the research landscape. "It has given our field a new look and a new life."

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Tomorrow: Nightmares and how to confront them