Ever since I was a kid I loved the idea of sleep learning: that you could put on headphones when you went to sleep and have conversational French when you woke up. I even tried it in college when, depressed by my mounting student loan debt, I decided I was going to go for a 4.0. All I got for my trouble was a few restless nights and a headache. Today, science can\u2019t promise you passive language learning, but there may be some hope for the lazy learners among us. A new study published in Nature demonstrates a fascinating phenomenon: sleep conditioning, a la Pavlov. Here\u2019s how it works.\r\n\r\n\r\n\r\nIt has been understood for a long time that sleep plays a critical role in forming memories. If you study something before you go to sleep, you will have a better understanding of it when you wake up. Your brain consolidates memories while you sleep, sorting through the day\u2019s information and storing it in retrievable packets in your brain, kind of like a biological filing system. Sleep\u2019s power to organize memory is profound, but until now we were unable to tap into this memory forming process while it was happening.\r\n\r\n\r\n\r\nAt the Weizmann Institute of Science in Rehovot, Israel, Anat Arzi and colleagues used classical conditioning techniques to teach 55 participants to associate sounds with smells while they slept. They exposed the sleeping subjects to a series of smells, ranging from pleasant odors like shampoo and deodorant, to unpleasant odors like rotting meat and fish. Along with each odor they played a specific sound. While the participants slept, they began sniffing in response to the sounds alone. They sniffed deeply for sounds associated with good smells, and more shallowly for sounds associated with bad smells.\r\n\r\nThe shocker: this behavior continued even after the subjects awoke! They were entirely unaware of the conditioning, after all, they slept through the lesson. And yet, their sniffing behavior in response to sound was undiminished, demonstrating that persistent learning and memory had taken place while they slept.\r\n\r\nWhile memorizing the associations between smells and sounds may not be entirely useful, there could be real potential in this sensory sleep memory formation process. Arzi: \u201cThis does not imply that you can put your homework under the pillow and know it in the morning. There will be clear limits on what we can learn in sleep, but I speculate they will be beyond what we have demonstrated.\u201d So get yourself a comfortable mattress, tape some sounds, have your partner waft some rotting fish under your nose, and see what happens.