Sleep deprivation may affect memory

The Mail Online states that “just one bad night’s sleep can have a dramatic effect on your memory – even leading to false memories”.

Though the results of this small experimental study involving US students are interesting, they're far from dramatic.

Researchers were interested in investigating whether sleep deprivation has an effect on a person’s susceptibility to false memories, which are surprisingly common.

In one famous study, many people claimed to have seen Bugs Bunny when visiting Disneyland as a child. This is plainly untrue, as Bugs Bunny is a Warner Brothers character.

In the first part of the experiment, people who self-reported having less than five hours sleep the night before the test were more likely to report seeing non-existent footage of the 9/11 plane crash in Pennsylvania.

People were then shown photos of two staged thefts, then given false written descriptions of it and questioned about what they had seen in the photos. In this test, there was no difference between people self-reporting sleep deprivation or not on recall.

In the second experiment, they took a separate group of students and then either let them sleep for a night or kept them awake, then saw how they performed on the same “misinformation” task. In this test, there was a mixed pattern of results, which does not give a clear picture of how, or if, sleep deprivation may be associated with false memories.

Where did the story come from?

The study was carried out by researchers from the University of California and Michigan State University, in the US. No sources of financial support are reported, and the authors declare no conflicts of interest.

The study was published in the peer-reviewed scientific journal Psychological Science.

The Mail Online and The Daily Telegraph’s reporting on the study overstates its findings. The Mail makes claims of a “dramatic effect on your memory”, while the Telegraph argues that the false memories related to sleep deprivation could cause relationship problems.

Neither news site noted the limitations of this experimental scenario and the fact that only a few of the results were statistically significant. This makes the relationship far from convincing.

What kind of research was this?

This was an experimental study designed to investigate whether sleep deprivation has an effect on a person’s susceptibility to false memories.

The researchers say that memories are not “recorded” in the brain, but are reconstructed from multiple sources, meaning they can be changed following exposure to altered information after the event or other suggestive influences.

People can sometimes have completely false memories, recalling clear and vivid experiences that never happened – imagined events are sometimes confused with actual memories.

The researchers say that many studies have explored what factors could be behind false memories, but sleep deprivation has not yet been explored. This is what they aimed to investigate.

The study was conducted in two parts. The first experiment tested whether self-reported sleep deprivation the night before was associated with false memories of a news event and false memories in a task giving misleading information (a “misinformation task”).

In the second experiment, people were deprived of sleep to see what effect this had on their performance in the misinformation task.

What did the research involve?

Experiment 1

A total of 193 university students were recruited (average age 20, 76% women). They were asked to keep a sleep diary every morning for a week, detailing the time they went to bed, how long it took them to fall asleep, when they woke, when they got out of bed and how many times they woke up during the night.

They then took part in the first experiment, where they completed a questionnaire on the plane crash in Shanksville, Pennsylvania, during the September 11 2001 tragedy.

This crash was never captured on video, but the participants were asked to answer “yes” or “no” to the question of whether they had seen “video footage of the plane crashing, taken by one of the witnesses on the ground”. Following this questionnaire, they were then interviewed about it, where the interviewers again repeatedly suggested that footage of this crash was widely available.

In the misinformation task, they were shown two sets of 50 photographs – one set showing a man breaking into a parked car, and the other showing a woman encountering a thief who steals her wallet. Around 40 minutes later they then read two textural descriptions of each photo set. Each description contained three false statements of the event shown, embedded within the correct information. A further 20 minutes later they were then asked multiple choice questions relating to what they had seen in the photos.  

Experiment 2

In the second experiment, they experimentally manipulated the amount of sleep in a separate group of 104 university students (average 19 years, 54% women) who took part in the misinformation test. All were reported to regularly sleep at least six hours a night. 

The study used a two-by-two design so that the influence of two different things could be examined – sleep deprivation or normal sleep – and the timing that certain parts of the test were completed, morning or evening.

In the evening, all participants completed validated mood and sleep questionnaires. 

Participants were then split into two.

One group was assigned to sleep deprivation or normal sleep and then completed all parts of the misinformation task at 9am.

This means that those participants assigned to the sleep deprivation arm of this experiment would perform all parts of the task while sleep deprived.

The other group was assigned to sleep deprivation or normal sleep and then shown the two series of photographs in the evening before sleep (or not). This means that the photos were seen by all participants when they were not sleep deprived. Then at 9am they completed the remaining two parts of the misinformation task – being shown the misleading text descriptions about the photos and then completing the multiple choice questions.

Those who were assigned to sleep were allowed to sleep for eight hours, from midnight to 8am. Those assigned to stay awake were not allowed to sleep and were kept awake by watching films, playing games, using computers, eating snacks and again completing the sleep and mood questionnaires every two hours.

What were the basic results?

Experiment 1

Participants reported an average of 6.8 hours of sleep, and 28 participants (15%) reported five hours or less of sleep the night before the study. They coded these 28 participants as having restricted sleep, and compared their results with the remaining 165 participants (85%).

When completing questionnaires about the plane crash, the restricted sleep group was more likely to answer "yes" when asked if they had seen footage of the plane crash.

However, in the follow-up interviews, they were no more likely than the normal sleep group to falsely say they had seen the crash.

On the misinformation task, there was no significant difference between the restricted sleep and normal sleep groups.

Experiment 2

The researchers found no main effect of the timing of the misinformation task alone, when comparing all people who completed all three parts of the task (photos, text descriptions and questions) in the morning, with those who had been shown the photos the night before instead. The researchers found they had no difference in their recall.

Similarly, there was no main effect of sleep deprivation alone. There was a trend for memory scores to be lower in the sleep deprived group compared to the sleep group, but the differences fell short of statistical significance.

There was some interaction between sleep and time of test, however. When people did all parts of the test in the morning, those who were sleep deprived were more likely to have falsely reported on the multiple choices questions something that didn’t happen in the photos.

However, when people were shown the photos the night before sleep/no sleep, there was no difference in false memories between the sleep deprived and sleep groups.

As expected, when given the mood and sleep questions in the morning, people who were sleep deprived were more sleepy and had poorer mood than those who had slept.

How did the researchers interpret the results?

On the first experiment, the researchers say the findings “tentatively suggest” that restricted sleep is related to memory suggestibility. On the second, they say that the sleep-deprived group was more likely to have false memories compared to the rested group, but only when participants were sleep deprived for all three stages of the misinformation task (i.e. all parts completed in the morning).

Conclusion

This experimental study is thought to be one of the first that has investigated how sleep deprivation may be associated with false memories.

In the first part of the experiment, self-reported restricted sleep the night before the test was associated with false questionnaire reports of seeing footage of the 9/11 plane crash in Pennsylvania (which doesn’t exist). However, people with restricted sleep weren’t more likely to give false reports when subsequently directly interviewed about it.

In these people, self-reported restricted sleep was not associated with poorer performance on the misinformation task.

In the second experiment, where they took a separate group of people and manipulated their sleep, there was some evidence that people who were not allowed to sleep were more likely to have false recall of the photos, but only if all parts of the test were performed in the morning (i.e. when people were sleep deprived). If they were shown the photos the night before instead (when not sleep deprived), on completing the task in the morning, there was no difference between sleep deprived and sleep groups.

Therefore, overall, the mixed pattern of significant and non-significant results does not give a very clear picture. There are also further important limitations, including:

• The small, specific groups tested – there were only two separate groups of 193 and 104 young, US university students. Other groups could give very different results.
• In the first test, the definition of sleep deprivation was self-reporting five hours or less of sleep the night before the test. This is likely to include many inaccuracies, including that people may not be able to give a very reliable indication of their sleep quality and quantity in the sleep diary questions used. Previous research has found that people often under-estimate the amount of sleep they get.
• There were also only 28 people in this “sleep deprived” group, making them a small group to compare against.
• Similarly, preventing a group of people from sleeping at all during one night does not give a very reliable proxy for sleep deprivation in the real life situation, e.g. a pattern of poor sleep quality and quantity persisting over a much longer time period.
• The tests used – asking people whether they have seen footage of the 9/11 plane crash in Pennsylvania, and giving them a test where they are shown photos of two incidents, then given incorrect descriptions of them – is also only a very restricted experimental test. They cannot reliably test how sleep deprivation may be associated with the recall of the wealth of our daily and lifetime experiences.
• Also, if there is an association between sleep deprivation and false memories, the study is not able to take into account the various confounding factors (e.g. psychological, health-related and lifestyle) that may be associated with this.

Overall, any association between false memories and sleep is likely to be complex and influenced by many factors. This single experimental study does not provide very clear evidence of a definite link.