A hormone, known to promote hunger, has been found to enhance exploratory sniffing in both animals and humans, according to a new study.
The findings suggest ghrelin may enhance the ability to find and identify food.
Researchers, led by Jenny Tong and Matthias Tschop at the University of Cincinnati, found the appetite-related hormone also influences smell.
The new study shows ghrelin, made mainly in the stomach, binds to molecules in the brain's olfactory bulb, suggesting the hormone is directly involved in odour processing.
"This new function of ghrelin was unknown prior to our discovery," said Tong.
"We think ghrelin is part of an important interface designed to help detect calories in our environment and to link those sensory inputs with the internal regulation of metabolism and body weight," she said.
Previous studies suggested sniffing might help people identify sources of nutrition, particularly during fasts when the sense of smell improves.
For this reason, the researchers predicted ghrelin, which normally spikes before meals, acts on olfactory regions and leads to behavioral changes - such as sniffing - to help spur food intake.
In this study, Tong and her colleagues measured how rats and people react to different odours. When small amounts of ghrelin were delivered directly to rats' brains, the animals sniffed more often.
The ghrelin-treated rats also avoided water with low concentrations of an odour associated with sickness more than untreated rats.
Nine humans who received ghrelin infusions also reacted to stimuli differently.
Each volunteer was directed to whiff unperfumed air or baby powder, banana, tomato, or rosemary chicken scents. Participants given ghrelin inhaled more deeply.
The study appears in the April 13 issue of The Journal of Neuroscience.