Thanks to advanced and digital technologies, a close study of the dreaming brain is possible. Dream researchers use neural-imaging tools range from EEG to PET scan to MRI to observe the brain's activity while dreaming. In addition to observing healthy brain activity, scientists also use cases of brain injury and illness as a way to learn about the brain mechanics of dreaming.
This approach -- of learning about the functions of the brain through abnormalities, injury, or illness -- is by no means just confined to the study of dreams. A great deal of what we know about the mechanics of the brain in general has come from observing what happens to human function when the brain has suffered damage. Changes to dreams - -their frequency, their characteristics -- are one sometime consequence of neurological illness and injury. Some of the earliest studies of the neurological underpinnings of dreaming used cases of brain injury gain insight about the areas of the brain involved with dreams.
In recent years, a number of important scientific breakthroughs in understanding dreams have come from research involving neurological conditions. Let's take a look at some of the most interesting and noteworthy cases of recent years:
In 2004, Swiss scientists shared the results of a study of a 73-year-old woman who lost all of her capacity to dream after experiencing a stroke that affected parts of her occipital lobe, located at the back of the brain. This part of the brain is deeply involved in processing visual information, including perception, color, spatial awareness, and movement detection. Not surprisingly, the woman experienced problems with her vision in the aftermath of her stroke. More unexpectedly, however, she also experienced a complete cessation of dreams. She'd previously been able to recall dreaming regularly, but after her stroke she had no recollection of any dreams at all. Her vision issues improved after several days, but her dreaming remained suspended. Scientists used MRI to identify the areas of the occipital lobe that had been affected by her stroke, including structures that are responsible for processing complex and emotional visual images and memories. Scientists also spent six weeks observing the woman's brain activity during sleep. Their results helped pinpoint areas of the brain -- specifically those involved in processing complicated visual information -- as likely playing a role in dreaming. Other studies of brain injury and brain illness have also implicated this same region of the brain in the dreaming process.
Their findings also helped to shed light on the relationship between REM sleep and dreaming. Even as the woman's dreaming was interrupted, she continued to move normally through nightly sleep cycles and the individual stages of sleep, including REM sleep. REM sleep has long been closely associated with dreaming. While it is clear that REM is an active time for dreams, and dreams that occur during REM may have particular -- and particularly vivid -- characteristics, sleep and dream scientists are now aware that the brain mechanisms of REM sleep and dreams are distinct, not one and the same. This particular study was one piece of research that contributed to a growing body of understanding about the independent mechanisms of REM sleep and dreaming.
Scientists from a number of French universities investigated the effects to dreaming of injury to parts of the brain's limbic system. The limbic system is deeply involved with emotion, memory, imagination, and some of our most basic and powerful motivations and drives, including appetite and sex. The 13 people included in this study had all suffered damage to parts of the limbic system -- specifically the basal ganglia -- which resulted in a neurological disorder known as auto-activation deficit, or AAD. People with AAD experience extreme apathy, and a striking lack of mental activity and processing. In essence, this condition is one of a blank and empty mind, one that does not engage in spontaneous thought or imagination. Scientists investigated how this neurological condition might affect dreams. They observed patients sleeping, and awakened them during REM sleep to have the report on any dream activity. Roughly a third of AAD patients reported some dreaming. Dreaming among AAD patients was dramatically less common than in neurologically healthy subjects, more than 90% of whom reported dreams. AAD patients' dreams were also significantly less vivid, colorful, and complicated. People with this condition dreamed briefly, often of very simple, basic actions and circumstances.
Researchers' results provide a number of scientific insights about how dreaming may work in the brain. The reduced frequency of dreams and the diminished complexity of dreams in AAD patients suggest -- as other research has -- that that the limbic system likely has an important influence over dreaming. The fact that dreaming occurs at all in patients with this type of neurological injury also may give credence to what's known as the "bottom-up" theory of dreaming, which posits that the process of dreaming is at least in part driven by activity in the brainstem -- which controls basic functions like breathing and heart rate -- rather than higher-level cognitive regions of the brain.
Study of brain conditions is also providing insight into how dream recall -- our ability to remember dreams after waking -- may function in the brain. Research of two brain regions -- the tempoparietal junction (TPJ) and the medial prefrontal cortex (mPFC) -- has indicated that lesions in these brain structures can result in the loss of ability to recall dreams. These areas of the brain are involved with sensory and emotional processing, among other functions. Building on these findings, scientists in France recently linked normal variations in activity in these brain regions to different levels of dream recall ability, among neurologically healthy people. The natural individual variation of activity in the TPJ and the mPFC may help to explain why some people can remember their dreams and others can't.
Even with pretty amazing technology at our disposal, dreams -- their function, their purpose -- remain relatively little understood. The study of dreams through brain accidents, abnormalities, and disease will likely continue to be a source of new details that enrich our knowledge of this most mysterious aspect of life.
Michael J. Breus, PhD
The Sleep Doctor™