Functional neuroanatomy of different olfactory judgments

Humans routinely make judgments about olfactory stimuli. However, few studi es have examined the functional neuroanatomy underlying the cognitive opera tions involved in such judgments. In order to delineate this functional ana tomy, we asked 12 normal subjects to perform different judgments about olfa ctory stimuli while regional cerebral blood flow (rCBF) was measured with P ET. In separate conditions, subjects made judgments about the presence (odo r detection), intensity, hedonicity, familiarity, or edibility of different odorants. An auditory task served as a control condition. All five olfacto ry tasks induced rCBF increases in the right orbitofrontal cortex (OFC), bu t right OFC activity was highest during familiarity judgments and lowest du ring the detection task. Left OFC activity increased significantly during h edonic and familiarity judgments, but not during other odor judgments. Left OFC activity was significantly higher during hedonicity judgments than dur ing familiarity or other olfactory judgments. These data demonstrate that a spects of odor processing in the OFC are lateralized depending on the type of olfactory task. They support a model of parallel processing in the left and right OFC in which the relative level of activation depends on whether the judgment involves odor recognition or emotion. Primary visual areas als o demonstrated a differential involvement in olfactory processing depending on the type of olfactory task: significant rCBF increases were observed in hedonic and edibility judgments, whereas no significant rCBF increases wer e found in the other three judgments. These data indicate that judgments of hedonicity and edibility engage circuits involved in visual processing, bu t detection, intensity, and familiarity judgments do not. (C) 2001 Academic Press.