A recent study at an Israeli university says people can learn while asleep, and later recall the information.

Prof. Noam Sobol and research student Anat Arzi at Rehovot's Weizmann Institute of Science employed a technique of associating particular odors or fragrances with sounds heard while sleeping.

Arzi told Xinhua on Tuesday that they used a simple form of learning called "classical conditioning" in order to teach 55 healthy participants in different stages of sleep to associate different smells with sounds.

The subjects were exposed to pleasant smells, like deodorant or scented soap, and unpleasant ones, like rotten meat and fish, during their sleep and the researchers accompanied each specific smell with a particular audible tone.

The subjects of the study sniffed strongly while they heard a tone associated with a pleasant smell, but sniffed weakly in response to a tone associated with an unpleasant smell.

The next day, the subjects kept on sniffing strongly or weakly to the relevant tone without any of the smells present, although they were not aware they were conditioned to associate between specific smells and sounds.

Subjects who were in various stages of the sleep cycle showed similar results. However, the sniffing responses were slightly more pronounced with those who learned to make the association during the rapid eye movement stage of deep sleep, which takes place in the later stages of slumber.

"While our experiment focused on the function of smell, it is possible that the sleep-learning process could manifest itself in other ways as well, and we plan to carry on and find them out," Arzi said, but cautioned that "it is too soon to tell what areas exactly those may be."

"We are now trying to implement helpful behavioral modification through sleep learning," she said. "We also want to investigate the brain mechanisms involved in this process and the types of learning that we can and cannot use during the different stages of altered consciousness such as vegetative state and comas," she said.

Arzi said that the study is just the "threshold" in studying the brain and its abilities during sleep.

The last serious study about sleep learning, called hypnopedia, was conducted more than 50 years ago in the United States, but since then no serious studies on the matter have been recorded.