SAN FRANCISCO--Ever wonder why your dreams can be so freakish? It's because your thought patterns are also bizarre in never-never land. Researchers have shown that concepts are more disjointed during REM sleep, in which dreaming occurs, than at other times. The finding, announced here Sunday at the Society for Cognitive Neuroscience's annual meeting, suggests that REM sleep is crucial for reorganizing thoughts and making fresh associations between newly learned facts.
Psychologists can test the brain's ability to connect concepts with a fast-paced word test, called a priming task. A subject must decide whether a string of letters is a word, and they tend to respond faster if they have just seen an associated word. For example, after seeing the word "right," people judge "wrong" to be a word in about a half second. But after being primed with a less closely related word, such as "thief," it takes people about 20 milliseconds longer to decide. And "paper" adds about 40 milliseconds to the decision. Thus the stronger the connections between related words, the faster the response.
Cognitive neuroscientist Robert Stickgold and his colleagues at Harvard Medical School tested whether dreamed thoughts, which can be strangely juxtaposed, are associated in a fundamentally different way from conscious ones. They recruited 44 subjects to sleep in their lab, then roused them during REM and non-REM sleep for a priming task. They found that immediately after REM sleep, a closely related prime did not help awakened dreamers process a word more quickly. But surprisingly, a weakly related prime did speed up word processing by about 25 milliseconds--a significant difference.
"This matches the phenomenology of dreaming," in which the dreamer makes unusual connections between ideas, Stickgold said. The finding is no surprise to Harvard psychologist Michael Hasselmo, who notes that the brain "has a completely different environment during sleep than during waking." He speculates that this strange cognitive terrain "may allow the brain to explore ... different interpretations of a new situation during REM."