A   In recent years, the Proustian phenomenon in which specific odours can trigger or evoke specific memories has become a major talking point among scientists. For example, Rachel Herz, a cognitive neuroscientist at Brown University in Providence, Rhode Island, has discovered how sensory memories are shared across the brain, with different brain regions remembering the sights, smells, tastes and sounds of a particular experience. "There is this unique connection between the sense of smell and the part of the brain that processes emotion," says Herz. Studies have shown that memories triggered by smells can be more emotional, as we have more detail, than memories not related to smells. When you inhale, odour molecules set brain cells dancing within a region known as the amygdala, a part of the brain that helps control emotion. Comparatively, other senses like taste or touch travel indirectly through other parts of the brain before they reach the amygdala. The direct link between odours and the amygdala may help explain the emotional potency of smells.

B   But the links don't stop there.The memory of smells has influence on other brain regions as well.In recent experiments, neuroscientists at University College London (UCL) asked 15 volunteers to view specific pictures at the same time they were exposed to unrelated odors. For instance, the subjects might see a photo of a duck paired with the scent of a rose, and then be asked to create a story linking the picture with the odour. Brain scans taken at the time revealed that the volunteers' brains were particularly active in a region known as the olfactory cortex, which is known to be involved in processing smells. A few minutes later, the volunteers were shown the same photo with no exposure to the rose smell. And in their brains, the olfactory cortex lit up again, even in the absence of the rose scent. The fact that this happened gives evidence to the idea that people's sensory memory is distributed and retained by multiple regions of the brain. “Imagine going on a seaside holiday," says UCL team leader, Jay Gottfried. "The sight of the waves becomes stored in one area, whereas the crash of the surf goes elsewhere, and the smell of seaweed in yet another place. There could be advantages of having memories spread around the brain. You can re-awake that memory from anyone of the sensory triggers."

C   Remembered smells may also carry extra emotional baggage, according to Herz. According to her research, memories evoked by odors are more emotional than memories evoked by other senses. In one recent study, Herz recruited 232 volunteers who had vivid memories associated with a particular perfume, such as Opium for women and Juniper Breeze from Bath and Body Works. She monitored the brainwaves of the volunteers as they sniffed that perfume and an unrelated perfume without knowing which was which. They were also shown photos of each perfume bottle. The act of smelling the specified perfume maximizes the level of brain activity with the volunteers, in a region called the hippocampus, which aids in the forming of memories.

D   Not only may odour-induced memories be more emotional, they are likely to be more detailed and vivid. Working with colleague John Downes, psychologist Simon Chu from the University of Liverpool started researching odour and memory partly because of his grandmother's stories about Chinese culture. He had noticed that as generations gathered to share oral histories, they would pass a small pot of spice or incense around; later, when they wanted to remember a story in as much detail as possible, they would pass the same smell around again. “It kind of fits with a lot of anecdotal evidence on how smells can be really good reminders of past experiences," Chu says. The claim has been backed up by scientific research. In one experiment, Chu and Downes asked 42 volunteers to tell a life story, then tested to see whether odours such as coffee and cinnamon could help them remember more detail in the story. The outcome was satisfying.

E   Despite such studies, not everyone is convinced that Proust can be scientifically analysed. In the June issue of Chemical Senses, Chu and Downes exchanged critiques with renowned perfumer and chemist Joseph Stephan Jellinek. Jellinek chided the Liverpool researchers for, among other things, presenting the smells and asking the volunteers to think of memories, rather than seeing what memories were spontaneously evoked by the odours. Chu defends his position, saying that it is difficult to statistically measure people's memories. Meanwhile, Jellinek has also been collecting anecdotal accounts of Proustian experiences, hoping to find out the sensory stimulus which elicits the experience. “I think there is a case to be made that surprise may be a major aspect of the Proust phenomenon," he says, “that's why people are so struck by these memories." We cannot be sure whether Marcel Proust ever experienced such a transcendental moment. Even so, his ideas regarding memory, written as fiction almost 100 years ago, continue to engage scientists today.