A hedonically complex odor mixture produces an attentional capture effect in the brain

A counter-intuitive property of many pleasant and attractive stimuli is that they are hedonically complex, containing both pleasant and unpleasant components. A striking example is the floral scent of natural jasmine, which may contain more than 6% of indole, a pure chemical which is usually rated as unpleasant. Using fMRI we investigate the hypothesis that the interaction between the pleasant and unpleasant components in the hedonically complex natural jasmine produces an attentional capture effect in the brain. First, to localize brain areas involved in selective attention to odor, we compared neural activity in response to jasmine without indole when participants explicitly and selectively attended to either its pleasantness or intensity, with neural activity when no selective attention was required. We then show that the superior frontal gyrus has increased activity both when selective attention is being paid to jasmine without indole, and also when no selective attention is required but an unpleasant component is added to it to produce a hedonically complex mixture. The attentional capture effect in the superior frontal gyrus by the mixture was related to the hedonic complexity of the mixture across subjects; could not be explained by salience, intensity, or pleasantness; and was specific to the superior frontal gyrus in that it was not found in other prefrontal areas activated by selective attention. The investigation supports the new hypothesis that the affective potency of stimuli with mixed pleasant and unpleasant components is related at least in part to the recruitment of mechanisms in the brain involved in attentional capture and enhancement.