Damaged dreams. An MRI scan of the patient's brain reveals the area destroyed by her stroke.

To Sleep, But Not to Dream

David is the Online News Editor of Science.

In 1997, a 73-year-old woman stopped dreaming after suffering a stroke. Now researchers believe the case provides the first compelling evidence that a small region deep in the back of the brain is critical for dreaming. The findings may help resolve decades of controversy in the field of dream research and shed new light on the purpose of dreams.

Whereas psychologists have long debated the meaning of dreams, neurologists have focused on their origins. Over the last century, studies of brain damage located specific regions that seem to be responsible for generating dreams. However, most of the patients also experienced other physical problems or were not given comprehensive neurological examinations, making it difficult for researchers to pinpoint these dream machines.

When neurologists Matthias Bischof and Claudio Bassetti began examining their 73-year-old stroke patient at the University Hospital of Bern in Switzerland, they realized they had a unique opportunity to solve the mystery. The researchers woke the patient up at various points during her sleep cycle and found that she couldn't recall any dreams--evidence that she had lost the ability to dream rather than the ability to remember her dreams. Despite her dream loss, the woman had no other neurological abnormalities, and thus the researchers concluded that the area of the brain affected by the stroke--revealed by magnetic resonance imaging (MRI) scans to be the right inferior lingual gyrus--is critical for dreaming. This region processes emotions and visual memories.

Brain-wave analysis of the patient's sleep patterns uncovered another surprise: The patient had a normal cycle of rapid eye movement (REM) sleep. Since the 1953 discovery that REM sleep is associated with dreaming, neurologists have argued about whether the two processes are actually linked. "This finding provides more evidence that these are separate events," says Bassetti, now at the University Hospital in Zurich, Switzerland. Because the patient was otherwise normal, Bassetti notes that the study challenges the belief that dreaming is necessary for mental well-being. The brain can apparently compensate, too; 3 months after the stroke, the patient began experiencing short dreams. Bischof and Bassetti describe their results in the online 10 September Annals of Neurology.

"This is a much better documented, more precise, and therefore more convincing study than anything that has come before," says Mark Solms, a neuropsychologist and dream expert at the University of Cape Town in South Africa. Solms believes the study will give dream researchers a specific area of the brain to test: "This may allow us to finally pin down the function of dreaming."

Related sites
Claudio Bassetti's home page
Current ideas about dreaming

Posted in Brain & Behavior