The concept of “sleep learning” has been around for a long time. Back in the 1980s, subliminal self-help cassette tapes were all the rage, promising to help sleepers learn new languages and skills, reduce their anxiety, and more—and to this day, there are plenty of audio recordings and apps that promise to help you learn while you snooze. But is it really possible for us to learn new information in our sleep?

In a recent article in The Guardian, neuroscientist and sleep specialist Jordan Gaines Lewis explained what actually happens when we try to learn while we sleep. 

According to Lewis, scientists have long doubted the efficacy of instructive sleep tapes—and with good reason. The first study to test sleep learning was conducted all the way back in 1956, when two researchers played a recording of 96 facts as volunteers slept, then asked the volunteers trivia questions upon awakening. They found the volunteers were unable to answer the questions—which ranged from sports statistics to topics in history and science—and concluded that sleep learning was “probably impossible.” 

More recent studies, however, have complicated that finding somewhat, according to Lewis. For instance, one 2014 study found evidence that volunteers learned foreign language word pairs better after listening to them in their sleep. Another study, meanwhile, found that releasing a subtle odor while volunteers studied a pattern of objects on a grid, then releasing that same odor as they slept, helped volunteers remember the patterns better the next day.

Even so, Lewis remains somewhat skeptical of these studies. He believes that, for the most part, the thing that actually helps us learn is sleep itself—not what we’re smelling or listening to. “Slow-wave or deep sleep has been recognised for some time as critical for memory consolidation–the stabilisation of memory from short-term to long-term,” he explains. “During slow-wave sleep, which tends to happen during the first half of the night, the firing of our brain cells is highly synchronised. When we measure sleep using electrodes attached to the scalp, slow-wave sleep appears as slow, high-amplitude oscillations.”

In the case of the 2014 language-learning study, Lewis believes it may have been sleep itself—rather than the recordings played during sleep—that helped volunteers remember the new language better than the participants who weren't allowed to squeeze in any shuteye. 

Lewis concludes, “So, yes, we can learn during sleep—a bit. However this is mostly limited to making subconscious associations, like pairing scents with images.” Which means, if you’re thinking about learning a new language, studying before bed might be more helpful than trying to study while you sleep.

[h/t: The Guardian]