Predictive templates created by the brain prepare people for smells before it even hits their nostrils, scientists from Northwestern University have suggested.
Published in the journal Neuron, the research used MRI techniques and cutting-edge, pattern-based analysis to determine the existence of predictive coding in the olfactory cortex of the brain.
This ability to prepare a sense for an incident before it occurs is essential for humans and animals, as it helps them act both more quickly and with greater accuracy to events taking place in their environment.
Jay Gottfried, MD, associate professor of neurology at Northwestern University Feinberg School of Medicine, explained: "We found that the entirety of the olfactory cortex we looked at did form predictive templates that were very specific to the targeted smell."
Using an MRI scanner, the researchers were able to analyse the brain activity before an odour was administered to establish if the brain had prepared itself for the smell.
Two scents were used in the study – watermelon and a Play-Doh like odour – and subjects were told which of the odours to expect before the trial began. A visual countdown was provided for the subject, and when they detected the smell they pressed a button.
Sometimes the odour was different to the smell subjects were told to expect and sometimes it was masked with other odours. The researchers found that when the scent was the same as the target identified, brain activity was more correlated.
"Our study confirmed the existence of predictive coding mechanisms in olfaction," Mr Gottfried said, adding that people often underestimate the importance of a sense of smell, using a bottle of milk which has gone off as an example.
"If your brain can successfully form a template of a rotten milk smell, then you would more accurately determine whether that milk is rotten and therefore you are less likely to get sick,' he said.
Advances in both genetics and genomics are improving understanding of how the sense of smell works. Sequencing mammalian genomes has recently helped scientists better learn how smell has evolved to suit the needs of different species.