In a study published September 10, 2004, in the online edition of the Annals of Neurology, scientists describe a patient who lost all dreaming, and very little else, following a stroke in one distinct region of the brain, suggesting that this area is crucial for the generation of dreams.
"How dreams are generated, and what purpose they might serve, are completely open questions at this point. These results describe for the first time in detail the extent of lesion necessary to produce loss of dreaming in the absence of other neurological deficits. As such, they offer a target for further study of the localization of dreaming," said author Claudio L. Bassetti, M.D., of the Department of Neurology at the University Hospital of Zurich in Switzerland.
These unique scientific observations began with an unfortunate event: a stroke suffered by a 73-year-old woman. When blood flow was disrupted to a relatively small area deep in the back part of her brain, she lost a number of brain functions.
Most of these disabilities were related to vision, which was not unexpected, since one of the brain functions localized to this area of the brain is the processing of visual information.
Fortunately, within a few days of the stroke, the visual problems had gone away. But a new symptom emerged: The patient stopped dreaming.
Such loss of dreaming--along with visual disturbances--following damage to a specific part of the brain goes by the name Charcot-Wilbrand syndrome, named for the eminent neurologists Jean-Martin Charcot and Hermann Wilbrand, who first described it in the 1880s.
The syndrome is quite rare, especially cases that lack symptoms other than dream loss. Bassetti, then at the University of Bern, and his colleague Matthias Bischof, M.D, realized that this woman's misfortune might provide valuable answers to the localization of dreaming in the brain.
For six weeks following the stroke, the researchers studied the patient's brain waves as she slept. They found no disruptions in her sleep cycle. The fact that REM sleep continued normally was significant, because dreaming and REM sleep occur together, though research has pointed to different brain systems underlying the two. These results appear to confirm that dreaming and REM sleep are driven by independent brain systems.
Before the stroke, the patient recalled, she had experienced dreams three to four times a week. She now reported no dreams, even when awakened during REM sleep.
With time, some dreaming function did return. A year after the stroke, she experienced occasional dreams, but no more than one per week. The dreams were of a reduced vividness and intensity compared to before the stroke.With MRI scans, Bischof and Bassetti determined that the stroke had damaged areas located deep in the back half of the brain. Recent research has shown that some of this region is involved in the visual processing of faces and landmarks, as well as the processing of emotions and visual memories, a logical set of functions for a brain area that would generate or control dreams.
But more interesting than the location is the fact that everything else about the woman seemed to be normal. She showed no signs of any problems with memory, attention or any other mental abilities, and beyond a few visual disturbances in the first few days, normal vision. “She has no other cognitive problems after a full clinical assessment,” says Bassetti. “She has a normal visual imagination.”
But did this woman really not lose any cognitive function other than the ability to dream? Can she form long term visual memories as well now as she could before the stroke? Since her cognitive abilities were not measured in detail before the stroke we can't be certain that she didn't lose any cognitive abilities.
At present, the functions of REM sleep are as elusive as those of dreaming. Adults spend a quarter of their nightly slumber in REM sleep, scattered throughout the night. The remaining time is spent deeper in unconsciousness. So REM may simply bring the brain back from deep sleep periodically to help us wake up if we need to, says Horne.
So then do people who don't experience REM sleep wake up more slowly than those who have REM episodes in sleep?
|Share |||Randall Parker, 2004 September 15 02:48 PM Brain Memory|