Many decades of research have shown that people cannot learn new information during sleep and then retrieve it once awake. Yet a growing body of work finds that unconscious associations made during sleep can affect waking behaviors. One new study found that pairing the smell of cigarettes with unpleasant odors made people smoke less during the following week.

Neurobiologist Anat Arzi and her colleagues at the Weizmann Institute of Science in Rehovot, Israel, recruited 66 smokers who wanted to quit and asked them to keep a smoking journal for a week before and a week after spending one night in the laboratory. Some subjects spent the night hooked up to devices that measured breathing and brain activity while they received puffs of the smell of smoked cigarettes followed by puffs of the odor of rotten eggs or decaying fish through a face mask. Other subjects underwent the same odor training during the day while awake. Smokers who got the putrid smells during the restful second stage of sleep cut their smoking by more than 30 percent during the following week. In contrast, subjects who received the odor treatment during rapid eye movement (REM) sleep, an aroused brain state that gives rise to dreams, had a much smaller reduction in smoking, around 12 percent. Smokers trained while awake did not change their smoking behavior.

Arzi presented the work last November at the annual meeting of the Society for Neuroscience in Washington, D.C. She says that the preliminary study was aimed at determining what the sleeping brain is capable of but that the findings might one day be developed into treatments for smoking or other addictive behaviors.