In new research published last week in the journal Current Biology, researchers from the University of Bern, Switzerland show how we can understand and retain foreign language vocabulary during specific periods of sleep, as well as unconsciously recall the relationships between the foreign word and the translation presented to us while we are sleeping.
Sleep and Memory: Probing the Sleeping Mind
At some point in their life, everybody has had the idea that everything would be so much easier if we could just learn new information while we slept, probably when they’ve been up late into the night studying for final exams.
For a very long time now, scientists have thought of this period of inactive sleep as an encapsulated state of mind that was largely shut off from the outside world around us.
Most sleep-learning research has been focused on studying the mechanisms at play during sleep that reinforce and cement new information learned in wakefulness, but little research has been done to date on the potential to learn new information while asleep.
University of Bern, Switzerland Institute of Psychology researchers Katharina Henke, Marc Züst, und Simon Ruch, participating in the Interfaculty Research Cooperation “Decoding Sleep” program, theorized that the sleeping brain was much more aware of the outside world than people were acknowledging.
The Role of the Active States of Brain Cells in Sleep-Learning
The experiment the researchers conducted tested whether or not a person is capable of forming new semantic connections between unknown foreign words and an accompanying translation, which were played to the subject while they were asleep.
Specifically, the researchers were looking for a link between connection-forming and the so-called “up-state” of brain cells. When a person enters deep sleep, our brain cells become more tightly coordinated and enter a brief period of activity as a whole, before jointly slipping into an inactive period afterwards—known as “up-states” and “down-states.”
The two states flip back and forth approximately every half-second, creating a strobe-like sequence of “up-states” during a sleep phase known as slow-wave sleep. These quick, regular flashes of activity were the crucial factor in the researchers' experiment.
They found that semantic associations between the words of an artificial language and their corresponding German translation were indeed formed, but only if the translated word of the pair was played 2, 3, or 4 times during an up-state in the person’s brain.
“These brain structures appear to mediate memory formation independently of the prevailing state of consciousness – unconscious during deep sleep, conscious during wakefulness,” said Züst, first co-author of the paper.
Memory Retention of Sleep-Learned Words Observed
“In how far and with what consequences deep sleep can be utilized for the acquisition of new information will be a topic of research in upcoming years”, says Katharina Henke, the author of a 2010 paper that theorized a new model of the relationship between memory and consciousness.
After waking, the subject of the experiment was capable of sorting and categorizing whether an artificial, and therefore completely unknown, sleep-played word denoted a large (”Guga”) or small (”Tofer”) object. This means that the subject was able to recall the relationships between sleep played pairs, such as “guga = elephant” and “tofer = key”, at a rate better than pure chance.
According to Züst, “it was interesting that language areas of the brain and the hippocampus – the brain’s essential memory hub – were activated during the wake retrieval of sleep-learned vocabulary because these brain structures normally mediate wake learning of new vocabulary.”
By detaching memory formation from consciousness, researchers hope to explore opportunities more sophisticated memory formation while asleep, but further research is needed to make any definitive claims in that regard.