Everybody dreams. But the frequency with which people recall their dreams varies considerably. One ongoing quest in dream research is to figure out what distinguishes people who remember a lot of their REM adventures from dream-nesiacs. And a new study, published in the journal Frontiers in Human Neuroscience, suggests that dream recall primarily hinges on waking up during sleep for at least two minutes at a time. A team of researchers from the US, Canada and France found that "high dream recallers" woke up for longer periods of time than "low recallers," i.e., people who don't spend their waking hours marveling over the crackpot tales of their unconscious brains.
Back in the 1950s, the researchers Nathaniel Kleitman, who discovered REM sleep, and William Dement, the “father of sleep science,” came up with the REM sleep hypothesis of dreaming, in which they attributed dream recall to frequent awakenings during REM. This idea cropped up in subsequent studies and fueled the widespread notion that people only remember their dreams if they wake up in the middle of them. Kleitman and Dement were most likely correct in identifying awakenings as the key to dream recall. But the current study casts doubt on their claim that awakenings need to take place during REM sleep, the vivid-dreaming stage of rest, to facilitate recollection.
For this study, researchers took another look at data, which they originally collected in 2014, on the sleeping brains of high and low dream recallers. High dream recallers were defined as people who remember at least three dreams a week, whereas low recallers remember two or fewer dreams per month. The data concerned all sorts of sleep-related characteristics, including participants' sleep architecture (the structural organization of sleep stages, as measured by patterns of electrical brain activity), Rapid Eye Movements, mid-slumber awakenings and responsiveness to sounds played during sleep.
Based on their reanalysis, researchers found one relevant difference between the two groups: On average, high recallers' awakenings lasted twice as long as those of low recallers. The duration (and not frequency) of awakenings was the "only candidate among the numerous tested parameters...to explain dream recall," researchers wrote. "The required duration for an awakening to allow for memory encoding was approximately two minutes."
High recallers probably wake up for longer periods of time because, as previous research has shown, they have higher-than-normal levels of activity in one region of the brain, called the temporo-parietal junction, when they're asleep. Revved-up T-P junctions make them reactive to outside stimuli, which means they're more likely than other people to wake up (and stay up, for a few minutes) in response to disturbing sounds like Amber alerts and thunderbolts. The resulting interludes of wakefulness give high recallers' brains the opportunity to cement whatever they last dreamt about into a lasting memory.
It makes sense, researchers explained, that shorter awakenings (under two minutes) wouldn't provide the same memory-encoding opportunities, because our typically spongy brains largely stop absorbing new information during sleep. And, upon waking up, it probably takes a little while for the brain to transition out of its sleep state and reboot its memory-encoding capabilities.