Feelings of hunger lead to increased smell perception by modifying the way specific receptors in our brain function, according to new research that may explain why smells drive increased food intake.
The study, published in Nature Neuroscience, examined the possible mechanisms behind hunger and our increased sensory perception to food when hungry, which many have suggested drive increased food intake - finding that when the sensation of hunger is felt, it triggers the activity of endocannabinoid receptors, which in turn activate the olfactory circuit, which then becomes more responsive, they explained.
Led by senior author Giovanni Marsicano from the Institut national de la santé et de la recherche médicale (INSERM) in France, the team explained that hunger triggers a set of mechanisms that encourage feeding, for example by increasing sensory perceptions such as the sense of smell. However the French team noted that the underlying mechanisms behind these effects remained poorly understood.
"We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odour detection," explained the research team - who added that the endocannabinoid system interconnects receptors located in the brain and involved in sensory perception.
It is therefore this biological mechanism that brings about the increased sensitivity to smell during hunger, explaining one of the reasons for food intake and attraction to food, concluded Marsicano and his colleagues.
The team studied the mechanisms using a mouse model - finding that CB1 cannabinoid receptors control a circuit that connects the olfactory bulb to the olfactory cortex.
"Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odour detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB [main olfactory bulb]," wrote the team.
"Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signalling, linking the feeling of hunger to stronger odour processing," they said. "Thus, CB1 receptor–dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behaviour."
The researchers added that they expect that the circuits involved in the olfactory system may be altered in obese or anorexic patients, and that sensitivity to smell may be more or less strong compared to normal.
They added that the identification of the biological and chemical pathways which control our heightened sense of smell and increased food intakes may allow better research in to - and management of - obesity and other eating disorders in the future.
Source: Nature Neuroscience
Published online ahead of print, doi: 10.1038/nn.3647
"The endocannabinoid system controls food intake via olfactory processes"
Authors: Edgar Soria-Gómez, Luigi Bellocchio, et al