Cognitive Daily

[This is our synchroblogging post in honor of PLoS ONE’s second birthday. Why not write your own?]

ResearchBlogging.orgEver wonder whether it’s better to study all night before a big exam, or to get a good night’s sleep, but maybe not have a chance to go over all the material? We know that memory consolidation can occur in sleep, but we also know that those extra hours studying can do some good. And then there’s the issue of false memories: who hasn’t had the experience of being completely convinced their test answer is correct, only to learn that it’s 100 percent wrong?

Inducing false memories is surprisingly easy. All you have to do is present people with a list of words to be memorized, like this:

Walking stick
Fishing pole

Then, 12 hours later, you test them: Was “backpack” on the list? How about “television”? “Mountain”? “Trapeze”? “Hike”?

It’s easy to remember the items that were on the list, especially considering they all relate to a common theme. It’s also easy to eliminate items like “television” and “trapeze.” But what about “hike”? That was the theme of the list, but it wasn’t on the list. Most people will falsely remember that it was, especially if they had to memorize several similar lists all at once. And they’ll be just as convinced that it really was on the list as any of the other items.

So how are these false memories formed? We know that memories are often consolidated in sleep, so the question arises: how does sleep affect false memories?

A team led by Susanne Diekelmann gave volunteers 18 such lists, each 15 words long, then systematically deprived some of them of sleep. Some were given the words at night (played via an audio recording), then required to stay awake until morning in the lab. Some were allowed a normal night’s sleep. And some were given the list in the morning after a normal sleep. All were retested nine hours later. Here are the results:


As you can see, everyone had plenty of false memories, but those who stayed up all night had significantly more. People who had a good night’s sleep were twice as likely to avoid false memories as those who stayed up all night. Everyone was just as accurate on normal memories — only false memories were affected in this way.

Then the researchers repeated the experiment over two nights. Everyone was given the words to memorize on the evening of the first day and tested on the morning of the third day (following the second night) This time, some participants were deprived of sleep on the first night, and some were deprived on the second night. Here are the results:


Only those who were deprived of sleep during the second night had a significantly higher false memory rate than those who slept both nights — sleeping during night 1 had no effect on the results. So it seems that exhaustion at the time of testing may be responsible for the results, not memory consolidation during sleep.

In a final experiment, the words to memorize were given in the evening and everyone was deprived of sleep the following night and tested in the morning. But one group of volunteers was given caffeine an hour before testing. The other group was given a placebo. Here are the results:


So caffeine wipes out the false memories! The placebo group was indistinguishable from the night-wake group in the first experiment.

But shouldn’t the people who didn’t get a good night’s sleep immediately after memorizing the words have had trouble consolidating those memories, and thus performed worse than those who slept through the night? The researchers say that sleep-consolidation isn’t as big a factor for recognition memory, as in this test, compared to other types of memory, such as free recall. It would be interesting to see this study repeated with a free recall test. Millions of last-minute students studying for exams want to know.

One thing’s for sure: if you do stay up all night studying for an exam, make sure you caffeinate yourself before taking the test!

Susanne Diekelmann, Hans-Peter Landolt, Olaf Lahl, Jan Born, Ullrich Wagner (2008). Sleep Loss Produces False Memories PLoS ONE, 3 (10) DOI: 10.1371/journal.pone.0003512


  1. #1 Gray Gaffer
    December 18, 2008

    – and please don’t think you can extend these results to 5 consecutive days continuous wakefulness, studying each night for the next day’s exams, on prescription-strength caffeine pills. Trust me, it doesn’t work that way. One night, yes, morning caffeine to reinvigorate, yes, but no more. I probably hallucinated the last three of those days, with predictable results.

  2. #2 N.B.
    December 18, 2008

    There are “prescription-strength” caffeine pills? *blink*

  3. #3 vineetgupta
    December 18, 2008

    The question of to drink coffee or not is a thorny one… On one hand it reduces false memories on the other hand drinking coffee increases the frequency of tip-of-the tongue experiences on the morning of the big viva. So what to do?!

  4. #4 carol
    December 18, 2008

    I’d like to see this study re-done with two groups – one that consumes coffee/caffeine regularly and one that doesn’t. I wouldn’t be surprised to see the best results with habitual caffeine consumers being given their fix and non-habitual caffeine consumers being left alone!

    (I should say “our” fix, rather than “their” fix. But you get my point.)

  5. #5 Ryan Fox
    December 19, 2008

    I always bring coffee into exams with me. Now I’m justified in doing so!

  6. #6 Aileen
    December 19, 2008

    I always thought it was caused by the examinee’s state of mind. People who cram their notes a night before are more tense, than people with a good night’s sleep. As a result, examinees who slept well perform better.

  7. #7 Alvin
    December 19, 2008

    As much as I love my coffee, when it comes to taking finals I have to fall back on those convenient little 200mg pills. There’s nothing worse than being halfway done with a final, surrounded by 50 people in all directions, with an uncomfortably full bladder in tow.

    Not to mention I always have a coffee in hand while studying; study caffeinated, recall caffeinated, right? State-dependent memory, or something like that – now all I need is the ability to take finals in my chair, on my computer desk. Preferably with some ambient “study music” playing in the background.

  8. #8 Gray Gaffer
    December 20, 2008

    “State-dependent memory” – yes, yes! Which is another indicator of why I failed – I am not normally in a state of extreme sleep deprivation.

    Yes, caffeine pills, blink: Alvin knows them. Sometimes need a prescription, sometimes not, depends on current Political Correctness and location. 200mg per x2 at midnight, 24 hrs awake if normal coffee consumption also indulged, can keep a normally healthy sprog going for a good five days before involuntary collapse. Typical cup of coffee is IIRC ~80mg.

  9. #9 Nash
    December 21, 2008


    I know we shouldn’t be judgemental, but you scare me. That kind of caffeine addiction has to be pathological!

    I made it all the way through graduate school and never had an exam so stressful that I needed to medicate myself. What are you studying anyway?

  10. #10 s
    December 23, 2008

    Did they publish any standard devs?

  11. #11 bowser
    December 24, 2008

    Calling these incidents of incorrect recall “false memories” is playing fast and loose with the term, and the idea.

    Errors in recall themselves are not necessarily, nor even sufficient, to claim the memory is a false one. Typically the idea of false memories, or “repressed memories” (the commonly used term), is more appropriately attributed to confabulation, the construction of a more complex memory that is believed by the confabulator to have been an actual event in the person’s life they experienced. This is merely remembering incorrectly, and the role that cueing and priming can have in that.

    I suggest the authors look seriously into the work of Elizabeth Loftus on the topic of false memories. (Loftus & Davis, 2006; Annual Review of Clinical Psychology, 2:469 – 498.) She has done other exemplary work on this as well.

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