Abstract
To investigate the organization of olfactory information in the anterior piriform cortex (aPC) of the guinea pig, we obtained high resolution mapping of odor-induced activation by optical imaging of intrinsic signals. One of possible codes for odor concentrations was shown in the aPC. Amyl acetate, butyraldehyde, butyric alcohol, ether and xylene were used as odor stimuli. Odor-induced cortical activation, which primarily originated in layer II, appeared in a narrow band beneath the rhinal sulcus over the lateral olfactory tract, corresponding to the dorsal part of the aPC (aPCd). Lower concentrations of odorants activated the rostral region of the aPCd, whereas higher ones induced caudally spreading activation, and the site at which neural activation reached its maximum extent depended upon odor concentration. Furthermore, the activated total area in the aPCd increased in proportion to concentrations raised to a power of 0.5 to 0.8. Unit recordings from the aPCd indicated a rostro-caudal gradient in odor-threshold among cortical neurons. These results suggest that the dorsal part of the anterior piriform cortex may be associated with odor concentration. A rostro-caudal gradient in axonal projections from mitral/tufted cells and/or in association fibers may play a key role in odor-concentration coding in the olfactory cortex. [Jpn J Physiol 54 Suppl:S19 (2004)]
