The New York Times article Study Uncovers Memory Aid: A Scent During Sleep says that smells may help us remember things better. They quote a study recently published in Science:
"The smell of roses — delivered to people’s nostrils as they studied and, later, as they slept — improved their performance on a memory test by about 13 percent."
Or this, from the Science magazine abstract:
"Sleep facilitates memory consolidation. A widely held model assumes that this is because newly encoded memories undergo covert reactivation during sleep. We cued new memories in humans during sleep by presenting an odor that had been presented as context during prior learning, and so showed that reactivation indeed causes memory consolidation during sleep. Re-exposure to the odor during slow-wave sleep (SWS) improved the retention of hippocampus-dependent declarative memories but not of hippocampus-independent procedural memories. Odor re-exposure was ineffective during rapid eye movement sleep or wakefulness or when the odor had been omitted during prior learning. Concurring with these findings, functional magnetic resonance imaging revealed significant hippocampal activation in response to odor re-exposure during SWS."
The Times article explains it in plain English, and the article in Science explains the scientific detals.
New York Times article:
Study Uncovers Memory Aid: A Scent During Sleep
By BENEDICT CAREY, March 9, 2007
A familiar scent can help a slumbering brain better remember things that it learned the evening before.
research at Science (subscription required for the full-text, or check your local library)
Odor Cues During Slow-Wave Sleep Prompt Declarative Memory Consolidation
Björn Rasch, Christian Büchel, Steffen Gais, and Jan Born
Science 9 March 2007: 1426-1429.
"In humans, a new memory formed in the presence of an odor is consolidated faster when the odor is used to induce neural activity in the hippocampus during subsequent sleep."