PET shows that odors are processed both ipsilaterally and contralaterally to the stimulated nostril

The olfactory nerve is the only cranial nerve with established ipsilateral primary cerebral anatomical projections. Whether these projections correspo nd to the functional pathways for monorhinal processing of odor perception is, however, unknown. We therefore studied cerebral blood flow (rCBF) with [O-15]butanol-PET in 18 healthy females during monorhinal smelling of singl e odors (OS) and odorless air (AS). Compared with AS, OS activated right am ygdala and piriform cortex (confluent cluster), right orbitofrontal cortex, left insula, right thalamus, and anterior cingulate. A post hoc analysis s howed that the first three regions were activated independently of the stim ulated side, but that right orbitofrontal rCBF was higher during the right nostril stimulations. Left insula was activated mainly by the right nostril stimuli, and right thalamus by the left nostril stimuli. Odors seem to be processed both ipsi and contralaterally, with a right hemisphere prepondera nce irrespective of the stimulated nostril. NeuroReport 11:2861-2866 (C) 20 00 Lippincott Williams & Wilkins.