Naps Can Make Our Brains 'Remember' Things That Never Happened
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Our memory is imperfect: We remember some moments but lose others like a problematic tape recorder. Sometimes, we even "remember" things that never happened — a phenomenon that researchers call "false memory" (and a reason why eyewitness testimonies can be misleading).

But where do these false memories come from? Previous studies have suggested that sleep plays a role in the formation of false memories, and in a recent small study, researchers homed in on one particular aspect of sleep, called sleep spindles, as the potential culprit.

Sleep spindles are quick bursts of brain activity during sleep, according to the study, which was published in December in the journal Neuropsychologia. They occur in one of the lighter stages of sleep, called Stage 2, which is defined by a slowed heart rate and no eye movement.

To study how sleep spindles may play a role in the formation of false memories, the researchers recruited 32 well-rested, non-caffeinated university students. The participants were shown a handful of words — all related to the same topic — before being hooked up to a polysomnography device, which monitors brain activity during sleep. The participants were then randomly assigned to one of two groups: a napping group or an awake group. The napping group was sent to a room with a bed and blackout blinds, while the awake group was told to watch a nature documentary or a Mr. Bean cartoon. The polysomnography device recorded brain activity to make sure the napping group was actually asleep and not just lying in bed.  [5 Surprising Sleep Discoveries]

After their respective activities, all of the participants were again shown a series of words and were asked if they had seen the words before. Some of the words were repeats from the first session, but some were new. What's more, the researchers threw in some "lure" words that were related to the topic of all the words but weren't shown to the participants before.

The researchers found that the students who napped were significantly more likely to fall victim to "lure" words and say that they had seen the words before, creating false memories. The findings were what the researchers had predicted based on previous studies.

But the researchers also wanted to test if one side of the brain was more gullible than the other. To do so,  the researchers designed the experiment so that the words flashed on the screen far to the left or far to the right in a visual field available to only one brain hemisphere at a time. If you blinked, you missed the word, said lead study author John Shaw, a psychology doctoral student at Lancaster University in England. But this wasn't to be annoying, he added; if the words stayed on the screen for longer, then participants' eyes would adjust so that both hemispheres could read the word.

The study found that the right hemisphere of the nappers' brains — which had a greater number of spindles during sleep, as recorded by the polysomnography device — fell more susceptible to "lure" words or false memories than the left. For example, the spindles might promote the word "sleep," telling the brain it remembers it from before, because it goes along with the general gist of words it had previously seen, such as "bed," "dream," "nap" or "snooze," Shaw said.

Sleep spindles have been linked to memory formation before, but previous "studies of [sleep] spindles have only examined true memories," not false memories, Shaw told Live Science. Indeed, sleep spindles are thought to play a very important role in consolidating short-term memory into long-term archives in the brain, and can also aid in cortical development. But this is the first study to find that sleep "spindles are accidentally creating [false] memories," Shaw said.

But don't get too mad at your brain — it's just trying to be efficient. "I think that the sleeping brain spends a lot of time and effort trying to identify the most important aspects of what was learned during the previous day," said Robert Stickgold, director of the Center for Sleep and Cognition at Beth Israel Deaconess Medical Center, who was not part of the study.  

Stickgold noted that the new study doesn't provide enough evidence to undoubtedly say that the right side of the brain is dominant in creating false memories during sleep. "It didn't hit [statistical] significance, but [it] was close," he told Live Science. "But the correlation with sleep spindles is stronger, and I suspect it is real."

Because the study was small, Shaw said he hopes to increase the number of participants with subsequent experiments, in addition to expanding from naps to following the brain's mischief across a full night's sleep.

Originally published on Live Science.