People who don't get enough sleep could be increasing their risk of developing false memories, a new study finds.

In the study, when researchers compared the memory of people who'd had a good night's sleep with the memory of those who hadn't slept at all, they found that, under certain conditions, sleep-deprived individuals mix fact with imagination, embellish events and even "remember" things that never actually happened.

False memories occur when people's brains distort how they remember a past event — whether it's what they did after work, how a painful relationship ended or what they witnessed at a crime scene. Memory is not an exact recording of past events, said Steven Frenda, a psychology Ph.D. student at the University of California, Irvine, who was involved in the study. Rather, fresh memories are constructed each time people mentally revisit a past event. During this process, people draw from multiple sources — like what they've been told by others, what they've seen in photographs or what they know as stereotypes or expectations, Frenda said.

The new findings "have implications for people's everyday lives —recalling information for an exam, or in work contexts, but also for the reliability of eyewitnesses who may have experienced periods of restricted or deprived sleep," said Frenda, who noted that chronic sleep deprivation is on the rise.

In a previous study, Frenda and his colleagues observed that people with restricted sleep (less than 5 hours a night) were more likely to incorporate misinformation into their memories of certain photos, and report they had seen video footage of a news event that didn't happen. In the current study, they wanted to see how a complete lack of sleep for 24 hours could influence a person's memory. [Inside the Brain: A Photo Journey Through Time]

The researchers used a process called "event encoding" to explore sleep's effect on memory: First, they showed 100 undergrad students — some of whom slept from midnight to 8 a.m., and others who stayed awake all night — a photo of a man tucking a woman's wallet into his jacket pocket.

Forty minutes later, the students read false information about the photo, which said that the man put the wallet in his pants pocket rather than his jacket. Finally, the researchers asked the students where they thought the man put the wallet, and how they knew that information.

"We found that compared to the participants who had slept, those who endured an entire night of sleep deprivation were more likely to falsely recall that the inaccurate, misleading information came from the original photographs," Frenda said.

The findings have wider implications for police interrogations, and shows how a lack of sleep might affect eyewitnesses' recollection of events.

"Police interrogations can go for hours and hours into the night," Frenda said. "This type of thing is less common today — but it does happen, and it is probably not a good idea if the goal is to protect the integrity of a witness's memory."

A better understanding of the mechanisms behind sleep deprivation and memory is needed before scientists can make specific recommendations for law enforcement processes, Frenda noted. However, allowing eyewitnesses to go home to get a good night's rest before testifying could also alter what they remember, since memories fade with time, he added.

Past studies have linked a lack of sleep to false memories, but these studies tested memory by using lists of words, which have less real-world significance than photos of events do, Frenda said.

The study was published July 16 in the journal Psychological Science.



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