Based in part on the previous version of this eLS article ‘Olfaction: Central Processing’ (2007) by John P McGann and Matt Wachowiak.
Olfaction: Central Processing
Published Online: 15 NOV 2013
Copyright © 2001 John Wiley & Sons, Ltd. All rights reserved.
How to Cite
McGann, J. P. 2013. Olfaction: Central Processing. eLS. .
- Published Online: 15 NOV 2013
Olfactory receptor neurons in the nasal epithelium detect a huge variety of airborne chemicals (termed ‘odourants’) and encode information about these stimuli in the form of action potentials. This code is then transmitted to the brain, where spatiotemporal patterns of neural activity represent the identity, concentration and temporal dynamics of the odourants. Neural processing of olfactory information at multiple levels in the brain mediates odour recognition, synthetic olfactory perceptions and provides feedback control to the initial stages of the olfactory pathway. This article presents some of the challenges in olfactory information processing and then reviews our current knowledge of the mechanisms by which the olfactory bulb and olfactory cortex represent odours and analyse olfactory information.
The chemical identity of an odourant is represented by the set of ORNs it stimulates and determines the odour's perceived quality.
The concentration of an odourant is represented jointly by the amplitude of the ORN response and the recruitment of ORNs expressing lower affinity receptors; this determines the odour's perceived intensity.
Each olfactory bulb glomerulus receives axonal projections from a set of ORNs expressing the same odour receptor.
An odour stimulates a subset of ORNs (based on their odour receptor expression) and thus drives activity in a corresponding subset of olfactory bulb glomeruli – this odour-to-glomerulus mapping is one of the most accessible codes in the nervous system.
Activity in olfactory bulb glomeruli is determined by a complex set of interactions among ORN sensory inputs, interneurons within and between glomeruli and modulatory inputs from other brain regions.
The set of mitral cells responding during odour presentation represents the chemical identity of the odour, whereas their firing frequency and timing provides additional information about the odour concentration.
Activity in mitral cells is shaped by complex interactions with inhibitory granule cells that interconnect mitral cells receiving disparate sensory input.
Neurons in piriform cortex respond to specific combinations of input from mitral cells in the olfactory bulb, thus selectively responding to certain odours or combinations of odours.
- odour coding;
- sensory coding;
- olfactory bulb;
- olfactory cortex;
- piriform cortex