Food-Related Odors and the Reward Circuit: Functional MRI

Eating is one of our basic needs, and food can be extremely rewarding. Different aspects of food can elicit the brain's reward system. In the present study we set out to investigate differences in brain activity evoked by pleasant food and non-food odors, with a particular focus on dopaminergic brain regions. We measured cerebral activity in 23 participants by means of magnetic resonance imaging, who were stimulated with three food odors (strawberry, orange, and mango) and three non-food odors (lily of the valley, jasmine, and lavender). We acquired functional images using a block stimulation design. Participants also evaluated pleasantness, intensity, and edibility of the odorants. Food odors elicited larger activations in the left postcentral gyrus, the left superior frontal gyrus, and in the midbrain. However, despite careful piloting, food odors were on average rated as significantly more intense than the flower odors. We therefore restricted the subsequent analysis to odors which were matched with regard to intensity and pleasantness. Thus, comparing strawberry and lavender odor yielded significant activations in the right cingulate, the midbrain, and the insula bilaterally. We further extracted the percentage of signal change from the global mean (beta) for all odorants in all subjects' ventral tegmental area, which revealed stronger signal change when subjects smelled food odors compared to flower odors. These results indicate that food-related odors may activate dopaminergic pathways in the brain, possibly due to a conditioned association.