Smell lights up whole concepts in the brain, through what psychologists call "associative networks," explains New Jersey-based Gilbert.
The science of smell got a big boost in 2004 when American researchers Richard Axel and Linda Buck won a Nobel Prize for discovering the large family of about a thousand genes for odour receptors and clarifying how the system works.
In his lab at Northwestern University, neuroscientist Jay Gottfried uses magnetic resonance imaging techniques to study the effects of odours on the brain. "Smell has very intimate access to parts of the brain involved in emotion and memory," he explains. "How a person perceives a smell is all about familiarity and cognitive context."