Naps Not Needed to Make New Memories

Naps Not Needed to Make New Memories
Credit: Maria Korneeva/Getty Images

Rats kept awake after exploring novel objects remembered the original items, but not where they’d seen them, raising interesting questions about human sleep.

Karen Hopkin: This is Scientific American’s 60-Second Science. I’m Karen Hopkin.

When someone tells you to “sleep on it,” they’re usually suggesting that you avoid making rash decisions. It is well-known that sleep can help you remember what you have learned.

Now, a nap might seem inconvenient when you’re cramming for an exam. But don’t worry. A new study has shown that rats who were awake when they encountered novel objects could recall seeing them a week later, sometimes better than rats who slept. That suggests that long-term memories can be laid down without having to lay down. These results are published in Proceedings of the National Academy of Sciences.

Marion Inostroza: We know that memory consolidation is promoted by sleep.

Hopkin: Marion Inostroza of the University of Tubingen. She claims that decades of research have shown that sleep can transform or consolidate recent experiences into lasting memories.

Inostroza: However, there’s also evidence for consolidation into long term memory during wakefulness.

Hopkin: So, sleep-deprived individuals can still learn stuff.

Jan Born: And against this background, we became interested in the question whether sleep is the only condition, is the critical condition, for the formation of long term memories.

Hopkin: Jan Born directs the institute of medical psychology and behavioral neurobiology at the University of Tubingen. The bottom line for Born is:

Born: Do we NEED sleep to form long-term memories?

Hopkin: To find out, the researchers allowed rats to investigate a novel object. The researchers then allowed the animals to explore a novel object in a “resting” cage. Some were allowed to sleep while others were kept awake.

Inostroza: And we do that by very gentle knocking the cage where the animal is placed. Or, by shaking the cage very carefully where the animal is.

Hopkin: One week later, the rats are returned to the testing cage and presented with the object they’d encountered previously…as well as one they’d never seen before. Now, if the rats remember the original item, they should spend less time nosing around it than they do sniffing the new new thing. It turns out that this is true for both those who rest and those who pull all-nighters…or all-afternooners. In this test, all rats remembered the objects.

Born: However, the kind of memories formed during sleep and during wake, they differ.

Inostroza: In our study we could at least disentangle two very different kinds of memories: [Memories] on the one side, memories which are for recognition of an object independent of context and on the other hand those memories which are context and space dependent.

Hopkin: So, rats who stayed awake were actually better at remembering the original object than their fully rested counterparts-but only when the item was presented in a new location. Rats who had had some shut-eye before their first study session seemed to be confused by the change in location and didn’t recognize familiar objects when presented in a new context. This suggests that their memories are context-dependent. However, for the rats who skipped the nap, it didn’t matter what context was.

Born: In life, of course, wake is always followed by sleep…

Hopkin: So Born says the two paths to memory consolidation most likely complement each other…with sleep putting waking memories in their proper place.

Born: So the wake state may, for example, serve to enhance the different events experienced during the wake phase, keep it in your memory, until you go into the sleep phase. The sleep phase…puts these objects and these events into the right context, which enhances episodic memory.

Hopkin: Now, as to whether you might want to avoid dozing after you cram for an exam…

Inostroza: I wouldn’t recommend this.

Hopkin: Of course, rats aren’t people. People are not rats. It’s not a fair question.

Born: I think it is a little too early to infer based on our results what students should do to be optimally prepared for an exam.

Hopkin: Nevertheless, Born does come down on the side of sleep.

Born: I’m still convinced, although we cannot infer this from our studies, I’m still convinced that sleep leads to the more effective, overall more effective, type of memory formation.

Hopkin: Plus, sleep gives your brain a chance to rest.

Born: When you are not fully rested, it is in general more difficult to retrieve any kind of memory in comparison when you are fully rested.

Hopkin: And the findings suggest that 40 winks should help you remember not just the who, what, and when…but also the wherefore.

For Scientific American’s 60-Second Science, I’m Karen Hopkin.

[The above text is a transcript of this podcast. ]

ABOUT THE AUTHOR(S)

    Karen Hopkin is a freelance science writer in Somerville, Mass. She holds a doctorate in biochemistry and is a contributor to Scientific American‘s 60-Second Science podcasts.

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