Neural mechanisms involved in odor pleasantness and intensity judgments

Olfactory processing in the human brain was examined using positron emissio n tomography. Twelve normal volunteers were scanned while smelling pairs of odors: they were asked to judge which odor was more pleasant in one condit ion, and which was more intense in a second condition; they also were scann ed while sniffing an odorless stimulus. As in prior studies, greater cerebr al blood flow was found in the right orbitofrontal cortex during both pleas antness and intensity judgments as compared to baseline. Cerebellar activit y was also seen, but contrary to expectations no activity was detected in t he primary olfactory (piriform) cortex. Only the pleasantness judgment elic ited additional activity within the hypothalamus, suggesting that this stru cture may be involved in affective processing that requires access to infor mation about internal state. (C) 2000 Lippincott Williams & Wilkins.