Pleasant or Unpleasant: Attentional Modulation of Odor Perception

Using positron emission tomography, we investigated whether regional brain activations differ as a function of attending to pleasant versus unpleasant components of odors. There were two experimental (attention to pleasantness and attention to unpleasantness) and one control (baseline) condition. The stimuli presented during the two experimental conditions were exactly the same (three binary mixtures, each consisting of one pleasant and one unpleasant compound), but the affective property to which participants’ attention was directed was different: They indicated with a mouse click whether each stimulus contained a pleasant (during attention to pleasantness) or unpleasant (during attention to unpleasantness) odor. During baseline, odorless stimuli were presented, and participants pressed the mouse button randomly after each one. Several brain regions were involved in both types of attention, and these included ventral striatum, right orbitofrontal cortex, and anterior cingulate cortex. Subtle differences were also revealed: Attending to pleasantness was associated preferentially with a sensory/perceptual network (piriform cortex and amygdala), whereas attending to unpleasantness engaged a component of the attentional (right parietal) network. Thus, we delineate neural substrates of attending to olfactory pleasantness and unpleasantness, some of which are common to both and others that are specific to pleasantness or to unpleasantness. Our results suggest that the view of the mesolimbic dopaminergic system as the reward network that responds selectively to positive reinforcers is somewhat limited: Our findings are more in keeping with a view of this set of structures as the salience system of the brain.