Scientists discover how smells can stir memory

Scientists believe they have discovered how a waft of perfume or the strains of a familiar melody can evoke a vivid memory.

A study has located the precise region of the brain that appears to be responsible for connecting an everyday sensation with something that has happened in the past. The area, the CA3 region of the brain's hippocampus, plays a critical role in the formation of memories that can stay with a person for life.

Researchers led by Dan Johnston, a professor of neuroscience at Baylor College of Medicine in Houston, Texas, said the CA3 region was essential for a phenomenon known as "pattern completion". He said: "That is the ability to recall memories from partial representations of the original." The CA3 region may be the part of the brain that initially captures a memory and prepares it for long-term storage. This may explain why people with a damaged hippocampus can remember events that occurred years ago but not what happened yesterday.

The study was based on an experiment in which mice were trained to escape from a maze using a set of visual clues. Genetically engineered mice that lacked a specific protein in the CA3 region could not remember how to get out of the maze when some of the clues had been removed.

Being able to recall the details of a memory from partial clues is thought to explain why humans can become sentimental over a song or a smell.

The study, run with the Massachusetts Institute of Technology and Hokkaido University in Japan, is published in the journal Science.