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.

“Further conclusions about this brain area and its role in dreams will require more studies analyzing dream changes in patients with brain damage,” said Bassetti.