Imagine going to sleep and waking up able to speak a foreign language. Or knowing all the facts for your upcoming history examination.
Unfortunately, despite the promises of some advertisements, it just isn’t going to happen.
Research over several decades has proven that you can’t learn new information while you sleep. Or has it?
A new study out by Israeli researchers indicates that at least some kinds of simple learning (via classical conditioning) can take place during non-REM sleep.
“Sleep-learning” allegedly conveys new information to an individual by playing a sound recording to them while they are asleep. This technique was supposed to be effective for teaching people to remember direct passages or facts, word for word.
Over 50 years ago, researchers (Simon, Emmons, 1956) concluded that sleep learning was “impractical and probably impossible”. They reported that material that had been presented during sleep was not recalled when the subject woke up unless alpha wave activity occurred at the same time as the material was presented.
Alpha activity indicates that the subject is about to wake up, so the researchers suggested that any learning that took place occurred in a waking state.
Other research studies since then also consistently debunked the myth of learning while you sleep; sleeping is not a prime time to learn new material. However, it has been demonstrated that sleeping helps your brain consolidate and reorganize memories of what you learned that day while you were awake.
Restful sleep has been shown to restore body and mind, clearly benefiting memory and creative problem solving with improved cognitive functioning upon waking – with the information that was learned while awake. The research showed that non-REM sleep could improve the memory of previously learned material and that REM sleep improved creative problem solving on mazes the subjects had been exposed to the day before.
On the other hand, a new study from the Weizmann Institute of Science has just been published that demonstrates that classical conditioning can occur during sleep. The study showed that people can learn during sleep, and that the learned information could unconsciously modify their behavior when they awoke.
The New Study
Professor Noam Sobel, research student Anat Arzi, team members from the Weizmann Institute’s Neurobiology Department, along with experts from Loewenstein Hospital and the Academic College of Tel Aviv-Jaffa recently published a study in Nature Neuroscience that reported the results of an experiment they conducted.
Their experiment investigated the effect of classical conditioning on a sleeping person; they chose classical conditioning as they could do it without waking the subjects.
Classical conditioning is a form of simple learning which was made famous by Pavlov and his dog.
They chose to utilize a tone followed by an odor, pairing them until the subjects responded similarly to just the tone without the odor. The researchers found that pairing tones and odors was advantageous as neither wakes the subject yet both are processed by the brain and even reacted to during sleep.
Sobel et al knew that the brain reacts the same to odors whether it is asleep or awake. That is, we inhale deeply when we smell something pleasant and shorten our inhalation when presented with an unpleasant smell. Furthermore, this ‘sniffing’ could be measured while asleep or awake. Although this type of conditioning appears uncomplicated, it is actually complex and associated with brain areas known for higher learning such as the hippocampus (involved in memory formation).
The researchers sprayed the participants with pleasant and unpleasant smells while they slept. As expected, the sleeping volunteers took longer breaths when there was a pleasant smell and shorter breaths when there was an unpleasant smell. Then they paired a tone with each smell (for example, a high pitched beep with the pleasant smell).
Following this, they played the high pitched beep without the smell and found that the volunteers took long breaths, perhaps subconsciously expecting the pleasant smell. They did the same thing with the unpleasant smell (rotting fish) using a different tone. After repeated pairings, the tone alone caused the volunteers to take a shorter breath.
The lesson learned through conditioning while they were asleep stayed with the participants after they woke up. Upon waking, the participants had no conscious memory of having learned anything while asleep yet when the researchers played the different tones (with no accompanying odors) they responded the same way as they had while asleep – longer breaths or sniffs to the high pitched beep and shorter breaths to the other tone.
REM Versus Non-REM Sleep
The research team conducted a second experiment to find out if this conditioning could happen only in a particular phase of sleep. They divided the sleep cycles into REM (rapid eye movement) and non-REM sleep and then initiated the pairings during just one phase or the other. They found that the learned sniffing response was considerably more pronounced during the REM phase but this did not carry over after waking.
On the other hand, when the conditioning took place during non-REM, the volunteers did transfer the learned associations upon waking. Sobel et al theorized that we may be more receptive to environmental stimuli during REM sleep but that “dream amnesia” (what makes us forget our dreams) exerts its influence on any learning or conditioning during that sleep phase.
Non-REM sleep is known to be significant for memory consolidation and this may well be playing a part in this type of sleep-learning.
Anat Arzi reported that she intends to continue investigating how the brain processes information in altered states of consciousness such as sleep and coma. She stated, “Now that we know some kind of sleep learning is possible, we want to find where the limits lie- what information can be learned during sleep and what information cannot.”