The idea of learning while sleeping, or hypnopaedia (hypnos, sleep; paedia, learning), is beguilingly seductive. It is a common prejudice that time spent sleeping is unproductive. From this point of view, the conversion of idle downtime during sleep into productive uptime is welcome. Furthermore, hypnopaedia promises to remove the drudgery and effort we experience when learning while awake. No wonder, throughout the 20th-century scientists kept revisiting this topic in their research. Despite their valiant efforts, no one has succeeded in convincingly demonstrating that learning can be transferred during sleep. However, hypnopaedia has been fodder for science fiction plots – most famously Aldous Huxley’s imagination of a dystopic future society (in his book “Brave New World”) where hypnopedia is used as a tool to manipulate the population. Huxley’s take on hypnopaedia reflects popular understanding in his time of the how and what of learning while sleeping. Young children are exposed to a recording of a mantra-like repetition of constructed truths as they sleep, and thereby get indoctrinated in a belief system that categorizes people into alpha’s ( “frightfully clever”) through intermediate categories called beta’s and delta’s through to the lowest category – gamma’s ( “stupid”); great fiction but not the stuff of science.
It is well established that sleep is when information that we acquire when we are awake gets consolidated and transferred from short term storage into long term memory. Can we improve the strength of memories through an intervention during sleep? This has been shown successfully in many studies where a cue (a sound or a smell) is paired with the learning event. When the same cue is presented during subsequent deep sleep, it causes a strengthening of the memory and this can be shown in a retest for the memory. It appears that the cue reactivates the memory trace during sleep thus strengthening the circuits that encode the memory. Such a technique has been used by a team of scientists at Princeton and Northwestern University to reinforce training to remove gender- and race bias. Bias is an unconscious programmed response of the brain based on heuristics derived from past experience. This ability to strengthen the effects of prior training to remove bias during a subsequent sleep session raises the disturbing possibility that such a tool could be used by an authoritarian institution to condition the behaviour of its citizens in less desirable directions. Another, and perhaps more likely scenario is that of a marketing company adopting such a technique to seed preferences for their product in the minds of unsuspecting consumers.
As seen in the examples above the strengthening of an already established memory by triggering the memory trace during sleep (Targeted Memory Reactivation) is no longer fiction. But can we learn something entirely new during sleep? Something to which we have never had prior exposure? The answer to this is a qualified “No”. It is doubtful that in the unconscious state that is sleep, we will be in a position to learn something complex like a formula in trigonometry since that would require a level of conscious awareness that is absent during sleep. However, can something much simpler be learnt – like an association between two sensory stimuli? Experiments have now shown that this is eminently possible. Scientists in New York carried out an experiment where a sleeping baby was exposed to a puff of air to its eye paired with a sound cue. When the baby was retested when awake with just the sound cue, it closed its eyes suggesting that the baby had learnt to associate the two stimuli during sleep. The pairing of odours has also been used to help people kick the cigarette habit, by simply exposing them during sleep to the smell of cigarettes paired to an offensive odour.
The unconscious brain when we sleep is far from idle. It churns through cycles of well-orchestrated activity, some of which is meant to reactivate memories as part of the transfer to long-term storage as stated above. The ability of the subconscious to process information and extract patterns when sleeping is probably an evolutionary adaptation that has evolved to use sleep as a time to encode pattern recognition circuits in the brain. These circuits are then used when we are awake – for example, a circuit that can predict while playing a tennis game the position of a tennis ball based on its speed and direction. Such shortcuts (heuristics) encoded by the unconscious brain are extremely useful in extracting patterns from and reacting appropriately to the complex torrent of information perceived by our senses when we are awake. Otherwise, the overload of sensory information would quickly clog the system.
We may not be able to learn when we sleep, but could we use the latent computational power of the brain when we sleep? Many historical discoveries have been attributed by their discoverers to insights that came to them when they slept – Ramanujan (mathematics of Infinite Series), Mendeleyeev (Periodic table) and Kekule (Benzene ring structure) are just a few examples from the world of science. Many famous artists have also attributed their creations to inspirations that came to them during a dream. All this suggests that the unconscious brain may be capable of feats of creativity that we remain unaware of. Tapping into this, especially when we sleep, is a project for systematic exploration. It is possible that, in the future, we may all be doing our best work – as inventors and artists and problem solvers of every kind – when we sleep. We will learn pretty much as we do now, but we may create new solutions to our problems as we sleep. Until then let us remember to discard the prejudice that sleep is idle downtime and sleep well!