Olfactory maps, circuits and computations

Abstract

Sensory information in the visual, auditory and somatosensory systems is organized topographically, with key sensory features ordered in space across neural sheets. Despite the existence of a spatially stereotyped map of odor identity within the olfactory bulb, it is unclear whether the higher olfactory cortex uses topography to organize information about smells. Here, we review recent work on the anatomy, microcircuitry and neuromodulation of two higher-order olfactory areas: the piriform cortex and the olfactory tubercle. The piriform is an archicortical region with an extensive local associational network that constructs representations of odor identity. The olfactory tubercle is an extension of the ventral striatum that may use reward-based learning rules to encode odor valence. We argue that in contrast to brain circuits for other sensory modalities, both the piriform and the olfactory tubercle largely discard any topography present in the bulb and instead use distributive afferent connectivity, local learning rules and input from neuromodulatory centers to build representations of behaviorally relevant properties of olfactory stimuli.

Localization of α1-2 Fucose Glycan in the Mouse Olfactory Pathway

“…Among them, superficial short-axon cells, some external tufted cells, interneurons in the external plexiform layer and granule cells mediate local neuronal circuits [Nagayama et al, 2014]. On the other hand, the middle tufted cells, internal tufted cells and mitral cells function as projective neurons of the MOB, and extend axons to the olfactory cortex through the LOT [Giessel and Datta, 2014]. We also located a large amount of α1-2Fuc glycan at the LOT.…”

“…These secondary neurons project axons to the olfactory cortex region in rodents, including the anterior olfactory nucleus, anterior and posterior piriform cortex and olfactory tubercle, through the lateral olfactory tract (LOT) [Giessel and Datta, 2014]. On the other hand, the vomeronasal system of most mammals is stimulated mainly by species-specific substances, and this pathway is separated from the main olfactory pathway.…”

Brain processing of a configural vs elemental odor mixture in the newborn rabbit

“…We recently revealed that after conditioning, competition occurs between the memory of the element odors (A and B) and the memory of the AB configuration (Coureaud et al 2014b). Here, such competition might impair matching of afferent information with the previously acquired representation of B (Boyd et al 2012;Chapuis and Wilson 2011;Giessel and Datta 2014), resulting in decreased activation in C AB vs PC AB , for which this competition and mismatch were not present. As decreased activation is observed as early as the OB, cortical centrifugal inputs on inhibitory neurons may participate (Boyd et al 2012).…”

“…At the peripheral level, it can be assumed that conditioning to B induces changes in firing rates of receptor cells activated by both odorants and/or the chemotopic pattern of B (Martin et al 2013). Moreover, the AB configural odor might compete and impair matching of afferent information with the previously acquired representation of B (Boyd et al 2012;Chapuis and Wilson 2011;Giessel and Datta 2014). Indeed, the OB which receives centrifugal modulatory inputs might have a key position to filter the afferent olfactory signals toward higher centers.…”

Construction of functional neuronal circuitry in the olfactory bulb

“…Due to space limitation, this review will only focus on OB circuitry and does not mention mechanisms of olfactory map formation by OSNs, which has been discussed previously [4][5][6]. For introduction to olfactory cortical circuitry, please see the following recent excellent reviews [7,8].…”