Functional reciprocal connections between olfactory and gustatory pathways.

The gustatory and olfactory chemosensory systems rely on receptors in the oral and nasal cavities that interact with the relevant molecules and generate receptor and action potentials, thus transmitting the effects of chemical stimuli to appropriate regions of central nervous system. The primary gustatory cortex (GC) is defined as the cortical region that receives direct fiber projection from the parvicellular part of the ventral posteromedial nucleus in the thalamus and the terminal labeling area is situated rostrally in the granular division (GI) and caudally in the dysgranular division (DI) of the insular cortex (IC) (Nakashima et al., 2000). In fact, unit recordings found gustatory responses of neurons from both the GI and DI (Ogawa et al., 1992), suggesting the location of the GC in both IC divisions. On the other hand, the primary olfactory cortex is defined as the region that receives direct fiber projections from the olfactory bulb (OB) (Price, 1987). The piriform cortex (PC) is the largest structure in the olfactory cortex and further the piriform region includes a nucleus localized in between the PC proper and the caudate-putamen, endopiriform nucleus (EPN). The PC is an important center before delivery of olfactory information to the higher system via the EPN (Haberly, 1998). In the primate, the orbitofrontal cortex is the highest chemosensory center where the olfactory and gustatory information might be integrated (Rolls, 1989), but in other mammalian species, no taste-sensitive neuron has been found in the orbitofrontal cortex. We report the olfactory and gustatory integrative region in the central nervous system from mapping data obtained from electrical and optical recordings.