What Dreams May Come

Imaging the brain during sleep

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For many years, dream experts relied solely on sleep journals to gather information and track sleep and dream activity. But, the study of human sleep has been enhanced in recent years by visual data made possible by functional imaging techniques, such as PET and fMRI.

Are You Sleep-Deprived?

Functional imaging techniques have also expanded the data-gathering possibilities in another arena connected to the wake-sleep cycle, that of sleep deprivation and the way that it affects cerebral responses.

In a society characterized by people's severe and prevalent failure to obtain an adequate amount of sleep, understanding

the impact of sleep deprivation on cognitive performance becomes critical.

"Our findings in patients with obstructive sleep apnea look very similar to the findings in healthy controls who go without sleep for 36 hours," says Sean Drummond, PhD, who has conducted extensive sleep-loss research at the University of California, San Diego.

Studies utilizing PET or fMRI have examined brain activation, cerebral function and behavioral performance of attention-demanding tasks following sleep deprivation. Researchers speculate that, when certain patterns of electrical and chemical activity that occur during sleep are interrupted, the brain's ability to function at optimum efficiency is impeded.

Yet, the ability of the brain to function following sleep deprivation would appear to vary with the task at hand.

The brain seems to be dynamic in its attempts to compensate for sleeplessness and perform the necessary functions anyway. Initial indicators point to a compensating adaptation pattern following sleep deprivation, when regions of the brain show an increased response to stimulation and provocation. The extent of such a response depends on the demands of the moment. But why the sleepy brain displays increased activity in certain regions and not in others remains unclear.

According to Drummond, who describes fMRI as the most valuable imaging method in his type of research, the advantage of neuroimaging is that "it allows us to study brain metabolism and function in humans, whereas before this was only possible with animals."

Moreover, Drummond says, "We'll soon be starting a study using functional neuroimaging to examine cognitive function in patients with insomnia."

And as research turns up more answers, researchers expect additional information about the plasticity of the brain and better insight into the ultimate functions of sleep. Also expected are partial answers to questions such as: Do shift workers, new parents, military personnel, active college students, late-night drivers and others typically experiencing sleep deprivation demonstrate cerebral adaptation to their situation or does the sharpness of their faculties diminish?

Also, can experts better understand and develop a neuropsychological profile of sleep-deprived patients, as well as patients suffering from insomnia or brain injuries? And, finally: What effects do naps, caffeine, pharmaceuticals and other sleepiness counter-measures have on cerebral responses?

In other words, for sleep researchers, there'll be no rest for the weary.

— B.W.

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But, the study of human sleep has been enhanced in recent years by visual data made possible by imaging techniques, such as PET and functional MRI (fMRI), which provide maps of the changes in regional neural activity during the distinct stages of sleep.

PET, for instance, offers a non-invasive way to study the changes in blood flow in the human brain during sleep, while fMRI, although widely used, has the disadvantage of the level of difficulty involved in recording the electro-encephalogram (EEG), measuring brainwaves, simultaneously with the fMRI signal.

Further, PET and fMRI make it possible to measure activity in different regions of the brain by monitoring how rapidly cells consume glucose or the rate at which blood is flowing – and to where. And they not only allow just a surface look at EEG structures, but they also provide a deep look into the brain.

Sleep rests the body, but not necessarily the mind. The brain doesn't merely click off at night. MRI pictures have shown furious mental activity from the base of the brain to its wrinkled covering, the cortex, or thinking dome. One theory holds that this "excitement" results from the consolidating of information learned during the day – retaining some memories and discarding others, as if going through the mail and tossing the junk. By making new connections, a form of unsupervised learning results in new associations and insights.

Enter the common perception: "It came to me in a dream." Meaningful information can be obtained when the neuroimaging data are explained in the light of our current knowledge about brain function, aided by insights contributed from fields such as neuropsychology, cognitive psychology, primate brain anatomy and cellular neurophysiology.

Channeling Freud

"The interpretation of dreams," wrote pioneer dream analyst Sigmund Freud more than 100 years ago in Vienna, Austria, "is the royal road to a knowledge of the unconscious activities of the mind."

For Freud – who began studying dreams after years of neurological research, but gave up because there was no pictorial way to map the brain in the pre-electronic-scan era – dreams were saturated with latent meaning, teasing us with clues to deep-seated, subconscious fears, fantasies, desires and dreads. And here people sit – and dream – a century later, still trying to decode the biology of just how we manufacture those dreams.

That's why, at the University of Pittsburgh Medical Centers Sleep Neuroimaging Research Center (SNRC), researchers delve into the brains of sleeping subjects with PET scans, usually employed to detect diseases such as cancer. Injecting subjects with mildly radioactive glucose, researchers trace the source of dreams to the limbic system, or the part of the brain that governs and controls emotions, influences senses such as sight and smell and contributes to the formation of memories. When people dream, the limbic system virtually explodes with neural activity, adding a layer and administering a jolt of drama.

"That's why so many dreams are emotional events during which we're running from danger or facing an anxious situation," says Eric Nofzinger, MD, the director of the SNRC and an expert clinician and clinical researcher in sleep disorders medicine. "The part of the brain that controls dreams also orchestrates our instincts, drives, sexual behavior and fight-or-flight response."

And as people dream, the brain's logic-governing frontal lobes disengage, which is why so many of the events or scenarios in our dreams seem bizarre or surrealistic. This mosaic of regions, some active and some not, may explain why humans often recall dreams of people that look nothing like the real-life version of them. Thus, perhaps the half-asleep portion of the brain governs facial identification.

Modern neuroscientists look at dreams in a somewhat different light than Freud did. Laboratory studies conducted several decades ago ended up linking dreams not to hidden urges, but to the firing of neurons and the oscillation of chemicals in the most primitive part of the brain during the phase of sleep characterized by "rapid eye movement," or REM.

REM, discovered in 1953, is a physiological state beginning about 90 minutes after the onset of sleep. Characterized by heightened brain activation, rapid (unseeing) eye movement, increased breathing and heart rate and genital engorgement, this sleep state continues to fascinate sleep experts. And by a simultaneous paralysis of bodily movement: humans are aroused yet fast asleep. This, in turn, causes experts to question: Did REM sleep become more or less synonymous with "dream sleep?"

When awake, people perceive something on the outside and then process the information in the cortex. Dreams reverse the process: They are internally generated, and then converted from abstract thoughts to concrete perceptions. And because the reflective system in the frontal portions of the limbic brain is inactivated, the dreamer accepts the dream scene without exercising critical judgment or evaluation.

Viewed from this vantage point, dreaming is seen as chaotic and random, an attempt by the sleeper's mind to account for all the heavy traffic driving through the brain. The higher brain centers – where memories, thoughts and emotions reside – are seen merely as passive responders.

Or, as Allan Hobson, MD, and Robert McCarley, PhD, both of Boston-based Harvard University's department of psychiatry, called it in their "activation-synthesis" model of dreaming, the mind makes "the best of a bad job in producing even partially coherent dream imagery from the relatively noisy signals sent up from the brainstem."

This would seem to part ways with the father of psychoanalysis, giving Sigmund the proverbial Freudian slip. But in recent years, new findings have led scientists to re-examine their grasp of the dream state and the brain, and to consider that the parts of the brain that control vision, feelings and memory might be playing a more active role than was previously thought.

Deconstructing Dreams

Recent neuroimaging studies have shown that human REM sleep is characterized by a specific pattern of regional brain activity that can be linked to particular dream features. And it is the neuropsychological analysis of dream content that would seem to offer new ways of interpreting dreams.

Additionally, several psychoanalysts have pointed to recent scientific findings as providing a biological foundation for at least some of Freud's deductions gained from treating neurotic patients of the late 19th and early 20th century.

"Twenty years ago," says neuropsychologist and psychoanalyst Mark Solms, PhD, of London's St. Bartholomew's Hospital, "Freudian dream theory seemed absolutely untenable. Today, what we know about the brain mechanisms of dreaming is far more compatible with what Freud inferred."

Some of the recent insights into the topography of dreaming have come from the development of neuroimaging techniques that have allowed investigators to actually observe the living, functioning brain. In one series of studies, the National Institutes of Health's Allen R. Braun, DO, and his colleagues used PET scanning to examine brain activation by measuring blood flow during both the REM and non-REM stages of sleep.

The resulting portrait of the dreaming brain indicated a subjective experience of dreaming consistent with psychoanalytic theory, characterized by vivid images, intense emotions and slivers of memory, all integrated in a way extremely different from the logical, orderly, self-aware manner of waking consciousness.

Moreover, that the emotional system is active during REM while the brain regions responsible for rationality shut down could be viewed as Freud's "ego" giving up control during sleep and allowing the "id" to express itself through the basic drives and appetites. This, in turn, generates dream imagery that is less restrained and more colorful.

Yet, there are contradictions, too. While Freud argued that the particular unconscious desires underlying dreams were censored and, thus, cloaked as something else, the PET study indicated that, during REM, the part of the brain responsible for generating such meaning-disguising symbols was inactive. All of which begs the question: Just where do dreams originate?

Most studies over the years have demonstrated that dreaming is most likely to occur during the REM stage, which, in a typical nights sleep, occurs regularly about every hour-and-a-half. Subjects awakened during REM report dreaming more than 80 percent of the time, compared to the 10 percent that subjects report when awakened during the other phases of the sleep cycle.

But, if these dreams are set off more or less automatically by the pattern of stages during sleep, how do experts account for all that dream-related material discussed routinely by therapists and their patients – the abiding psychological conflicts, the residual childhood traumas and the expression of unconscious desires?

Perhaps the REM stage is not the only stage of sleep during which dreams can be triggered. After all, non-rapid eye movement sleep (NREM) does account for about 80 percent of our sleeping time.

Suppose, for example, that necessary stimulation occurred during the stage just before falling asleep at night, or during the stage just before awakening in the morning. And suppose that the level of censorship and disguise that Freud suggested is applied to unconscious motives – as a way of keeping certain thoughts and emotions that people are reluctant to admit from intruding on their consciousness – is less active and effective than he first thought.

Braun has suggested that it may be time to put the focus on Freud aside. "Perhaps," he says, "it is simply the ghost of Freud getting in the way."

The primary aim of the Sleep Neuroimaging Research Program is to identify function changes in different regions of the brain across the wake/sleep cycle in health vs. disease, in the hopes of discovering alterations in function related to different disease states, and thus providing clues to appropriate treatment for particular disorders.

Their approach to studying brain function during sleep is to combine several research methods in sleep analysis and functional brain imaging, such as polysomnography with spectral analysis of the EEG, PET studies of regional cerebral brain glucose metabolism and fMRI studies of the brain. These methods provide high temporal and spatial resolution for measuring brain function during sleep.

With funding from the NIH, private foundations and the medical field, the Sleep Neuroimaging Research program studies a spectrum of disease states including depression, insomnia, aging and obstructive sleep apnea.

But Nofzinger, who has pioneered methods to define the brain mechanisms of human sleep disorders using functional neuroimaging, admits that only so much can be determined from imaging.

"We know that it's not just the random firing of neurons during REM sleep," he says. "There's some method to the madness of dreaming: We're still left with having to look at the psychological content of dreams."

— Bill Wine is a Pennsylvania-based freelance writer. Questions and comments can be directed to editorial@rt-image.com.