Olfactory functions are mediated by parallel and hierarchical processing

How the human brain processes the perception, discrimination, and recogniti on of odors has not been systematically explored. Cerebral activations were therefore studied with PET during five different olfactory tasks: monorhin al smelling of odorless air (AS), single odors (OS), discrimination of odor intensity (OD-i), discrimination of odor quality (OD-q), and odor recognit ion memory (OM). OS activated amygdala-piriform, orbitofrontal, insular, an d cingulate cortices and right thalamus. OD-i and OD-q both engaged left in sula and right cerebellum. OD-q also involved other areas, including right caudate and subiculum. OM did not activate the insula, but instead, the pir iform cortex. With the exception of caudate and subiculum, it shared the re maining activations with the OD-q, and engaged, in addition, the temporal a nd parietal cortices. These findings indicate that olfactory functions are organized in a parallel and hierarchical manner.