"During sleep and dreaming, part of the brain -- the higher visual cortex -- is working as if seeing images," he said. "Since the contents of a verbal report were predicted only from brain activity immediately before awakening -- zero to 15 seconds before -- [it may be that we] only remember contents related to brain activity [we experience] immediately before we wake up."
While one expert said the results are intriguing, he was cautious. "The results are interesting, but in view of previous disappointments relating brain activity to complex visual experience, one would like to see this replicated," said Dr. Irwin Feinberg, a professor emeritus at the University of California, Davis.
Feinberg emphasized that the research was not designed to determine a cause-and-effect relationship. "It's a correlation of brain activity and visual experience, largely statistical and purely by association," he said. "It does not shed light on the function of sleep or the function of dreaming within sleep."
But Feinberg said the researchers' focus on non-REM sleep is interesting and valuable. "Non-REM sleep constitutes 75 percent of our sleep; REM is only 25 percent. Nature knows what it needs, so the fact that non-REM occupies such a large percentage and occurs first suggest that it is of far greater importance than is REM."
Learn more about dreams and sleep from the National Sleep Foundation.
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