Dreams and Memory

Sleep consolidates memory, and the evidence is now large: Jenkins and Dallenbach (1924) found less forgetting across a night’s sleep than across a day awake, Wilson and McNaughton (1994) recorded the rat’s hippocampal place cells replaying the day’s maze during slow-wave sleep, and Rasch, Büchel, Gais, and Born (2007) cued the replay in people by releasing a rose scent during slow-wave sleep that had been present at learning, and improved recall the next morning, a technique now called targeted memory reactivation. Slow-wave sleep serves the memory of facts and places; REM sleep is implicated in skills and in the emotional memory.

Whether the dream itself is part of the work, or only its visible exhaust, is the open question. Stickgold et al. (2000) had subjects play Tetris and found the falling blocks in their sleep-onset imagery, in amnesic patients too, who could not remember having played; Wamsley et al. (2010) had subjects learn a virtual maze and nap, and those who reported dreaming of it, however obliquely, improved far more than those who did not, a finding since replicated. The dream was not the maze; it was the maze transformed, which is what consolidation does.

Dreams do not replay. Fosse, Fosse, Hobson, and Stickgold (2003) matched 299 dream reports against the dreamers’ diaries and found an episode reproduced whole in under two per cent; what appears is fragments, recombined, with the emotional charge kept and the context dropped. The hypothesis that the dream is the brain finding associations it would not find awake has a test: Cai et al. (2009) found a nap with REM, and not one without, improved performance on a remote-associates test of creative problem solving.

The dream that solves the problem has a literature of anecdote (Kekulé’s snake, Loewi’s frog hearts, Mendeleev’s table) and some data: Barrett (1993) had students incubate a chosen problem for a week, and about half dreamed of it, with a quarter reporting a solution that judges accepted. The dreams were literal more often than symbolic, and the problems that yielded were the ones that needed an image. The Journal’s advice to note the day’s concern beside the dream is the researchers’ own.

Sources

• Rasch, B., Büchel, C., Gais, S., and Born, J. (2007). “Odor cues during slow-wave sleep prompt declarative memory consolidation.” Science 315.
• Stickgold, R., et al. (2000). “Replaying the game: hypnagogic images in normals and amnesics.” Science 290.
• Wamsley, E. J., et al. (2010). “Dreaming of a learning task is associated with enhanced sleep-dependent memory consolidation.” Current Biology 20.
• Fosse, M. J., et al. (2003). “Dreaming and episodic memory: a functional dissociation?” Journal of Cognitive Neuroscience 15.
• Cai, D. J., et al. (2009). “REM, not incubation, improves creativity by priming associative networks.” PNAS 106.
• Barrett, D. (1993). “The ‘committee of sleep’: a study of dream incubation for problem solving.” Dreaming 3.

A review of the literature for readers; not medical advice.