Much of the animal training you see, whether it’s at SeaWorld or at a puppy class, is rooted in classical conditioning, the kind of training Pavlov demonstrated when he showed that dogs can be made to salivate at the sound of a bell that repeatedly paired with food.
In our waking hours, we experience classical conditioning all the time. For instance, every time your phone makes a beep, you look at it. Because you’ve so long associated the sound of the beep with – hold on. My turn in Words With Friends.
Pavlov and, later, BF Skinner, argued that classical conditioning is working on us during all of our waking hours. It happens in our own responses to bells and alarms, but also to things as subtle as words – a word being, itself, just an arbitrary set of sounds paired with some idea or feeling enough times that one eventually equals the other. Pavlov was especially interested in pairing arbitrary stimuli with sleep in order to induce it. That typically means “the repetition of some form of words, describing sleep, articulated in a flat and monotonous tone of voice,” he said in a 1927 lecture. Such words are, of course, conditioned stimuli which have become associated with the state of sleep."
But what about the learning that happens during those non-wakeful hours? We already know sleep is a time when the brain defragments, sifting the important things of the day into memory, and processing them so your brain can find them later. But what about acquiring new knowledge? Think of all that time that could be spent not just filing away but actually learning new two-letter words.
In a recent study published in Nature Neuroscience, researchers at the Weizmann Institute in Israel used classical conditioning to train people to associate pleasant and malodorous smells with particular sounds in their sleep. Subjects were exposed to tones accompanying bad odors – specifically, rotting fish and meat – and different tones accompanying nice odors, like shampoo and deodorant. (The choice of smell, I think is kind of a flaw in the study, since, following, say, a break-up, the smell of Pert and Old Spice could easily be classically conditioned to evoke negative feelings. And if you grew up with a lovely grandpa who had pickled herring breath, you may have been classically conditioned to have nice feelings about rotting fish. But I digress.)
I regress: The study found that, with enough paring, in their waking hours subjects took more shallow breaths following the tones paired with the bad smells, and took deeper breaths following the tones that had been paired with the good smells, even when no smells were ever presented.
Similar studies have yielded analogous results. In 2010, Columbia University researchers found that sleeping newborns learned the association between a tone and a puff of air; they quickly began to predicatively react to the puff following the tone.
By now, much of the sleep literature – which, incidentally, is great to read before bed – shows that sleep can stabilize and enhance previously-formed memories, as well as integrate these into existing memory networks, and extract emotionally valuable elements. But this new study shows that it’s possible to form a totally new memory while you sleep.
The question is, how much and what kind of stuff can you actually learn? Anat Arzi, one of the study’s authors, says that learning more complex information should be possible. Not that you’ll be able to just play the Middlemarch audiobook to study for your thesis defense. “There will be clear limits on what we can learn in sleep, but I speculate that they will be beyond what we have demonstrated,” he told Nature. It’s still unclear, for instance, if the neural networks involved in sleep learning are similar to the ones used when you’re awake.
But the first easy step: training humans out of behaviors or phobias. “We are now trying to implement helpful behavioral modification through sleep-learning,” says Arzi. “We also want to investigate the brain mechanisms involved, and the type of learning we use in other states of altered consciousness, such as vegetative state and coma.”
Of course, you don’t need to pile electrodes onto a sleeping baby or rub deodorant under your partner’s nose while playing a Sigur Ros record to figure out that you can learn in your sleep. Why, just this morning, while asleep, I was the subject of a similar study, in which I exhibited a response to the sound of a tone that I’ve long associated with dread. The classically conditioned stimulus (CS) caused a classically conditioned reflex (CR): a flailing arm motion, which led to the secession of the noise. Result: I was late for work again.
Illustration by Guido Scarabottolo.