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INSIGHT REVIEW NATURE|Vol 444|16 November 2006|doi:10.1038/nature05405
Smell images and the flavour system in the human brain
Gordon M. Shepherd1
Flavour perception is one of the most complex of human behaviours. It involves almost all of the senses, particularly the sense of smell, which is involved through odour images generated in the olfactory pathway. In the human brain, the perceptual systems are closely linked to systems for learning, memory, emotion and language, so distributed neural mechanisms contribute to food preference and food cravings. Greater recognition of the role of the brains flavour system and its connection with eating behaviour is needed for a deeper understanding of why people eat what they do, and to generate better recommendations about diet and nutrition.
Many humans regard their sense of smell to be of minor importance. The dominant role that smell has in sensing the flavours of the foods we eat and influencing what we like to eat is largely unrecognized. This is unfortunate, because our diet is causing a public health crisis in many western countries. Knowledge of the importance of smell to the perception of flavour and the formation of cognitive and emotional responses to foods and beverages could help to improve health and prevent chronic conditions such as obesity and diabetes.
The aim of this article is to review recent advances in the brain mechanisms of smell perception and to put forward several hypotheses for integrating these mechanisms into current theories of the neural basis of flavour as a complex multisystem percept. My hope is that this will help bridge the divide that impedes neuroscientists, behavioural psychologists, food scientists, nutritionists and public-policy makers from communicating effectively across disciplines about why we eat what we do and how to achieve healthy diets. I focus on three critical aspects of the brain mechanisms of smell: how odour molecules are represented in the form of odour images as the basis for smell perception; the importance of retronasal smell for flavour perception; and the close relationships between the brain mechanisms for flavour and the brain systems for emotions and cravings.
Odour molecules are represented by odour images
Odour stimulation of olfactory sensory cells in the nose involves odour molecules interacting with olfactory-receptor proteins. The discovery of the genes that encode...