The Neural Response of Deep Brain Structures to Odorant Stimulations: A Manganese-Enhanced MRI Study

An increased understanding of how odors are processed in the central nervous system may provide comprehensive information about the neural basis of odor-related behavior and learning. In this study, we investigated how different odors are processed from the olfactory bulb to the deep cerebral structures through various olfactory pathways. To do this, we employed a novel mangariese-enhanced magnetic resonance imaging (MEMRI) method to map the activity-dependent functional connectivity, of the olfactory and non-olfactory pathways associated with various odorants. Our MEMRI data revealed odor-specific neural pathways that correspond to different odorant stimulations, suggesting that different neural circuits may process different odorants. Among the odorants tested, formic acid, an alarm pheromone, stimulated not only the primary and secondary olfactory pathways but also the mesolimbic neural circuit, which overlaps with the dopaminergic neural pathway. Linalool, which is a major component of aroma oils, showed high Mn2+ uptake in the hypothalamus, which plays a role in the stress response through the secretion of corticotropin-releasing hormone (CRH), and consequently, the stimulation of corticotropin secretion. Acetone mainly activated the primary olfactory pathway, whereas saline acted as a non-odorous trigeminal stimulus. Taken together, our functional MEMRI using anatomic standardization and statistical analyses could be a promising in vivo imaging method to map neural connectivity, enabling further understanding of the neural processing of different odorants.