January 21, 2004
REM And Slow-Wave Sleep Needed For Memory Consolidation

Duke University researchers have found studying rats that memory formation occurs in the slow-wave and rapid eye movement (REM) sleeping states. (same article here and shorter press release here)

In their study, the researchers placed about 100 infinitesimal recording electrodes in the brains of rats, in four regions involved in memory formation and sensory processing. Those brain areas included the hippocampus, which is widely believed to be involved in memory storage, and areas of the forebrain involved in rodent-specific behaviors. The scientists employed the same neural recording technology that Nicolelis and his colleagues used to enable monkeys to control a robot arm, an achievement announced in October 2003.

The researchers next exposed the rats to four kinds of novel objects in the dark, since largely nocturnal rodents depend on the sense of touch via their whiskers to investigate their environment. The four objects were a golf ball mounted on a spring, a fingernail brush, a stick of wood with pins attached and a tube that dispensed cereal treats.

The researchers recorded and analyzed brain signals from the rats before, during and after their exploration, for several days across natural sleep-wake cycles. Analyses of those signals revealed "reverberations" of distinctive brain wave patterns across all the areas being monitored for up to 48 hours after the novel experience.

According to Ribeiro, "We found that the activity of the brain when the animal is in a familiar environment does not 'stick' -- that is, the brain keeps moving from one state to another. In contrast, when the animal is exploring a novel environment, that novelty imposes a certain pattern of activity, which lingers in all the areas we studied. Also, we found that this pattern was much more prevalent in slow-wave sleep than in REM sleep."

Conversely, previous studies by Ribeiro and his colleagues demonstrated that the activation of genes able to effect memory consolidation occurs during REM sleep, not slow-wave sleep.

"Based on all these results, we're proposing that the two stages play separate and complementary roles in memory consolidation," he said. "Periods of slow-wave sleep are very long and produce a recall and probably amplification of memory traces. Ensuing episodes of REM sleep, which are very short, trigger the expression of genes to store what was processed during slow-wave sleep." In principle, this model explains studies such as those by Robert Stickgold and his colleagues at Harvard University, showing that both slow-wave and REM sleep have beneficial effects on memory consolidation, he said. According to Nicolelis, the new experiments remedy shortcomings of previous studies.

Of course what we all want is to be able to more easily store selected memories. Suppose more sophisticated sleeping drugs are developed that can selectively cause humans to spend more time in slow-wave and REM sleep. Will that boost memory formation? Suppose it did. I think one would want to exercise restraint in the use of such drugs. Do you want to remember the most boring details of your most boring days? I think not. It might even make sense to crowd your most important learning-intense activities into particular days so that you can remember new knowledge from those days in special intense memory formation sleeping sessions.

The genes identified that are up-regulated by the REM stage of memory storage are a point of particular interest. Another approach that might boost memory formation would be induce the expression of genes involved in memory formation. The problem, though is that a drug that upregulated their expression might be too broad in its effects causing the genes to be expressed all the time rather than just in the phase of REM sleep when memories are normally consolidated.

Drugs capable of inducing specific sleeping states and drugs capable of turning on genes used in particular sleeping states hold out the potential of creating states of the mind that would be hybrid states that are between sleeping and waking states. Whether those hybrid mental states would end up being useful in practice remains to be seen. Perhaps it will eventually be possible to use sleep state regulating drugs in the following way: One could study a subject really intensely for an hour or two and then hook oneself up to an automatic drug dispensing device (which might even be an embedded device) that would release drugs that would throw one very quickly and successively into slow-wave and REM sleep states to consolidate the memories of what one was studying. Then the drugs would be stopped and another drug would bring you back awake with the last couple of hours of memories consolidated. Using this approach one might be able to then cycle through several cycles of learning and sleeping states in a single day. This would allow humans to escape from some of the limits caused by the evolutionary legacy of our ancestors being exposed the 24 hour cycle of light and dark caused by the period of rotation of the Earth back before Edison's invention of the electric light bulb.

The full text of the article is available free on-line in the journal Public Library of Science Biology (PLoS Biology) in three formats. First, a synopsis of the work:

Brain Activity during Slow-Wave Sleep Points to Mechanism for Memory
Full-text | Print PDF (2607K) | Screen PDF (326K)

The research paper for the work:

Long-Lasting Novelty-Induced Neuronal Reverberation during Slow-Wave Sleep in Multiple Forebrain Areas
Sidarta Ribeiro, Damien Gervasoni, Ernesto S. Soares, Yi Zhou, Shih-Chieh Lin, Janaina Pantoja, Michael Lavine, Miguel A. L. Nicolelis
Full-text | Figures | Print PDF (11762K) | Screen PDF (732K)

PloS Biology even has a list of news articles reporting on this paper here.

Share |      Randall Parker, 2004 January 21 07:11 PM  Brain Memory

khalid iqbal said at January 29, 2004 5:46 PM:

have a lot of sleep

Rachel said at December 30, 2005 6:55 AM:

At what point in sleep does slow-wave and REM sleep take place? Beginning, middle, end?

joe said at May 6, 2007 12:05 AM:

What the hell. I'll answer the question even though it's two years old. (I'm sort of avoiding writing an essay).
Think of sleep as a cycle rather than a progresstion. Going to sleep, a person transitions from arousal (consiousness) through sleep stages 1 - 4. Stage 3 and 4 is slow wave sleep (SWS). Most people stay in SWS for about 30 minutes before the cycle reverses. When sleepers should reach stage 1 they go into REM sleep. Typically, people will go through about 4 cycles of sleep in a night. Each cycle SWS gets progressively shorter and REM longer.

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