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It has long been known that sleep plays a role in establishing new memories. As long ago as 1924, Jenkins and Dallenbach showed that memory for syllables from a list was dramatically improved if people slept between studying the list and being tested rather than remaining awake during that period. The benefits of sleep for memory have since been shown across many studies and with many forms of memory.
A specific phase of sleep in particular, deep (or slow-wave) sleep, is thought to play a critical role in strengthening memories. This type of sleep can be measured with electrodes on a person's scalp. In recent years, researchers have tested whether cuing people with sounds during this phase of sleep (without waking them up) improves memory for information that was learned with the sounds while awake.
The results have been striking.
In a study published in Science, Rudoy and colleagues had people learn the locations of images on a grid, such as a cat in the lower left-hand corner of a screen, or a teapot in the upper right-hand corner. The images were accompanied by their corresponding sounds. So, the cat would appear along with a “meow”, and the teapot would appear along with a whistling sound. Then, the participants went to sleep while wearing electrodes on their heads to measure the different phases of sleep as they slept. When their brainwaves indicated that they were in deep, slow-wave sleep, the researchers played some of the sounds that had been heard earlier while learning the locations of images on the grid, like the "meow". When a person had awakened from sleep, the researchers tested his or her memory for the locations of the images on the grid. The person had to try to place each image into its correct location on the grid by moving it. What was fascinating was that people had superior location memory for those images whose sounds were played during slow-wave sleep compared to those whose sounds were not played during sleep.
More recently, Antony and colleagues (2012) demonstrated that this type of sleep-cuing is not limited to memory for learned locations of visual images on a grid: It also benefits the type of skill learning that occurs when learning things like how to play a musical instrument. When participants learned to play a musical sequence on a piano keyboard by following moving colored circles on a screen to learn the sequence, they were better at playing the sequence later if the melody itself had been played during slow-wave sleep.
In short, cuing memories during slow-wave sleep using sounds can dramatically enhance those memories, whether they are primarily visual memories or memories for motor skills like playing a sequence on a piano.
So, how do we do this at home to strategically benefit our own memories and abilities?
One simple method might be to study, learn or train while listening to particular pieces of music and then play those same pieces of music softly throughout our sleep so as to be sure to hit the slow-wave sleep.
However, new technologies and smartphone apps may make it possible for us to strategically strengthen memories as we sleep in a more sophisticated fashion. Take, for example, the Zeo system for tracking your sleep phases as you sleep (update: Zeo went out of business). Like other smartphone apps that interface with brainwave electrode devices, such as this meditation app or this music-from-brainwaves app, the Zeo system uses electrodes that you wear on your head. By wearing the electrodes to bed, Zeo's app will record your brainwaves as you sleep, giving you data on how much time you spent in the various phases of sleep during the night. Its SmartWake feature will even allow you to set a time range in which you would like to be woken up so that your alarm selectively goes off during a “good” phase of sleep from which to be awakened.
The SmartWake feature is explicitly designed NOT to wake you up during deep sleep (as that is a terrible time to be woken up). However, if users were allowed flexibility enough to control the phase of sleep in which sounds are presented, as well as to control the sounds themselves (as you might when choosing the chime or bell sound for your alarm), as well as how loudly it presents the sounds, we might just be able to strategically set our devices to cue us with specific sounds during slow-wave sleep in order to enhance our memories. You would want to set the sounds’ volume to be just loud enough to hear them (in order to trigger memories during slow-wave sleep), but not loudly enough to wake you from slow-wave sleep.
A sleep app with this type of flexibility could lead to endless possibilities for the future of memory enhancement and skill development. And an app with this flexibility is surely just around the corner.
