How does your brain pass the time while you're sleeping? In a study designed to apply state-of-the-art techniques to this old question, Sidarta Ribeiro and his colleagues at Duke University in Durham, North Carolina, recorded over a hundred neurons continuously over the course of the normal sleepwake cycle in rats, focusing on four major forebrain areas that are essential for rodent-specific behaviors.

Halfway through the recording time, animals were transiently allowed to explore novel objects placed in their cage. The researchers found that in all the forebrain areas examined the neuronal firing patterns recorded when the rats initially explored the new objects reappeared for up to 48 hours after these objects were removed. This reverberation of neuronal activity that they recorded was most significant during slow-wave sleep (a state that accounts for nearly 40% of a rat's life), decreased during waking periods, and was highly variable during REM (Rapid Eye Movement) sleep.

In this study, Ribeiro et al. demonstrate that long-lasting neuronal reverberation following novel waking experiences can occur in several forebrain sites and is strongly enhanced during slow-wave sleep. Because neuronal reverberations are sustained for long periods, this may support a mechanism to recall and amplify memories until they are effectively stored. On the basis of differences observed between REM and slow-wave sleep in this and previous studies, the authors propose that the two phases of sleep play separate and complementary roles in memory consolidation. Thus, the two stages of sleep give the brain a chance to process the novel events of the day in peace.

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Contact: Hemai Parthasarathy
hemai@plos.org
415-624-1205
Public Library of Science
20-Jan-2004

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