| Odorants have long guided approach and avoidance behavior, such as finding food and mates and eluding predators and harmful substances. We now know much about how these volatile molecules bind to the hundreds of types of olfactory receptors in the nose, and how the brain controls movements, but much less is understood about how those odors are translated into actions. Here we use psychophysical and chronometric methods, to model human olfactory perception, combined with functional magnetic resonance imaging (fMRI), to probe which brain regions are involved in the decision-making process. We investigated the temporal unfolding of an olfactory decision, from sensation (detection) through perception (odor qualia), identity (lexico-semantic representation), pleasantness (valence), and edibility, to the temporal accumulation of olfactory evidence toward a choice threshold, and the associated confidence in that evidence. We show that humans are surprisingly quick and accurate in identifying and matching odors to word labels, and that this mediates the processing of their valence and edibility. We provide the first evidence for the role of the right orbitofrontal cortex (OFC), and left anterior temporal pole, in linking odor perception and it lexico-semantic representation. We also advanced models of two-alternative forced-choices, by demonstrating that for difficult decisions choice bounds collapse over time to allow for more efficient decision-making. We localized the first evidence of a temporal integration of perceptual information signature in the human brain, in bilateral OFC. And finally, we showed that while taking more time to accumulate evidence can in some instances increase perceptual accuracy, people have a difficult time gauging how confident they should be in their accuracy. |
