Olfactory Processing Mechanisms in Mammalian Systems

The mammalian olfactory system transforms chemical stimuli into neural representations that guide behaviour, memory and emotion. At the periphery, olfactory receptor neurons in the nasal epithelium detect volatile molecules and project axons to the olfactory bulb, where signals are organised into discrete glomeruli. Within the bulb, mitral and tufted cells relay filtered information to cortical and limbic targets, notably the piriform and entorhinal cortices, while interneurons modulate circuitry via lateral inhibition, shaping spatial and temporal patterns of activity. In the piriform cortex, distributed ensemble codes integrate identity and intensity features, exploiting both spike count and spike timing. Downstream, multimodal convergence underpins associative learning and memory. Throughout the system, oscillatory rhythms coordinate local and long-range interactions, and adult neurogenesis in the bulb contributes to plasticity and long-term olfactory memory. Advances in molecular profiling have revealed subclass-specific connectivity rules, and computational models now capture how early-activated receptors and antagonistic interactions normalise responses to complex mixtures. Dysregulation of these circuits is implicated in neurodegenerative conditions, where altered coherence and plasticity serve as biomarkers and therapeutic targets. Collectively, these mechanisms illustrate a highly dynamic network that balances sensitivity, specificity and adaptability, with wide-ranging implications for artificial sensing, neuromorphic engineering and interventions in disease.

Research from Nature Portfolio

Recent studies have demonstrated that a small subset of the earliest activated receptors forms a concentration-invariant “primacy code” for odor identity, enabling decisions within 100 ms of inhalation by reading early spike latencies in the olfactory bulb. Computational models indicate that such a code can be decoded by cortical circuits to achieve rapid and robust recognition across varying concentrations. Complementary work has shown that behavioural sensitivity to odours is determined by the single highest-affinity receptor in the repertoire: deletion of this receptor alone shifts detection thresholds, while increasing its neuron count does not further enhance sensitivity. These findings establish fundamental principles by which receptor affinity and temporal dynamics govern perceptual thresholds and identity coding in mammalian olfaction.

Olfactory Processing Mechanisms in Mammalian Systems publication trend

The graph below shows the total number of articles in olfactory processing mechanisms in mammalian systems across all publications each year (not limited to Nature Index journals).

Technical terms

Olfactory receptor neuron (ORN): A specialised sensory neuron that detects odorant molecules and transmits signals to the olfactory bulb.

Glomerulus: A spherical structure in the olfactory bulb where ORN axons converge and synapse onto mitral and tufted cells.

Mitral/tufted cells: Principal projection neurons of the olfactory bulb that convey processed olfactory information to cortical regions.

Primacy coding: A coding scheme in which the earliest-activated receptors or neurons carry crucial information for concentration-invariant odor identification.

Lateral inhibition: A circuit mechanism whereby activated neurons suppress neighbouring neurons to sharpen spatial or temporal contrast in sensory signals.

Piriform cortex: A primary olfactory cortical area that integrates bulb outputs into distributed ensemble representations for perception and memory.

References

1. Neuronal organization of olfactory bulb circuits. Frontiers in Neural Circuits (2014).
2. Differential Axonal Projection of Mitral and Tufted Cells in the Mouse Main Olfactory System. Frontiers in Neural Circuits (2010).
3. Molecular signatures of neural connectivity in the olfactory cortex. Nature Communications (2016).
4. Complementary codes for odor identity and intensity in olfactory cortex. eLife (2017).
5. Antagonism in olfactory receptor neurons and its implications for the perception of odor mixtures. eLife (2018).
6. A primacy code for odor identity. Nature Communications (2017).
7. Single olfactory receptors set odor detection thresholds. Nature Communications (2018).
8. Distinct Olfactory Bulb-Cortex Neural Circuits Coordinate Cognitive Function in Parkinson’s Disease. Research (2024).
9. Activity-dependent local protection and lateral inhibition control synaptic competition in developing mitral cells in mice. Developmental Cell (2023).
10. Beta and gamma oscillatory activities associated with olfactory memory tasks: different rhythms for different functional networks?. Frontiers in Behavioral Neuroscience (2014).
11. Cellular and Behavioral Effects of Cranial Irradiation of the Subventricular Zone in Adult Mice. PLOS ONE (2009).