The Scent Trail – Encoding Memory

Marcel Proust’s 3,200 page novel À la recherche du temps perdu has in it the famous scene where dipping pastry into his tea flooded him with his childhood memories. It was the odor which provoked it, and it has gone into psychoanalytical literature as the most famous literary evidence of the power of scents in retrieving long-lost memories.

In a recent controlled study over sleeping mice at the Duke University Medical Center, neuroscientists Stephen Shea and Richard Mooney have tried to elucidate the cellular and molecular basis of how memory of scents are locked up in the brain, only to be retrieved later years afterward, and provoking a strong recall of original incidents. While asleep the animals were administered electric shocks which triggered noradrenaline release; at the same time strong odors were presented to their noses: of food and urine of other mice. The study published in a recent edition of Neuroscience is an important milestone in our understanding of odor-processing.

Later when awake, the introduction of the same odors provoked distinct behavioral changes, proving that in the presence of adrenaline, odors are codified as memory traces, even though they were asleep. It was an earlier hypothesis which this study lends support to, that noradrenaline plays an important role in preserving memories of scents due to processing in the olfactory bulb in both humans and mice. Long lasting memories are very important for social bonding and this study may have implications for understanding how long lasting memories are linked with emotion. While odors are thought to be extremely important in the social behavior of many animals, in humans its role is still not well understood. Part of this is due to the fact that in humans, the cerebral cortex has assumed an over-riding importance compared to the brains of animals lower down the evolutionary scale.

However, there are many amongst us who remain Proustian at heart, and odors are emotionally important. The waft of Mother’s rhubarb pie may remain an important link to her in the future, long after she is gone.

Reference

S. D. Shea, L. C. Katz, R. Mooney (2008). Noradrenergic Induction of Odor-Specific Neural Habituation and Olfactory Memories Journal of Neuroscience, 28 (42), 10711-10719 DOI: 10.1523/JNEUROSCI.3853-08.2008