Odor stimuli: Not just chemical identity
- 1University of Sussex, United Kingdom
In most sensory modalities the underlying physical phenomena are well understood, and stimulus properties can be precisely controlled. In olfaction, the situation is different. The presence of specific chemical compounds in the air (or water) is the root cause for perceived odors, but it remains unknown what organizing principles, equivalent to wavelength for light, determine the dimensions of odor space. Equally important, but less in the spotlight, odor stimuli are also complex with respect to their physical properties, including concentration and time-varying spatio-temporal distribution. We still lack a complete understanding or control over these properties, in either experiments or theory.
In this review, we will concentrate on two important aspects of the physical properties of odor stimuli beyond the chemical identity of the odorants: 1. The amplitude of odor stimuli and its dynamics and 2. The spatio-temporal structure of odor stimuli in a natural environment. Concerning these issues, we ask the following questions:
1. Given any particular experimental protocol for odor stimulation, do we have a realistic estimate of the odorant concentration in the air, and at the olfactory receptor neurons? Can we control, or at least know, the dynamics of how odorants arrive at olfactory receptor neurons?
2. What do we know of the spatio-temporal structure of odor stimuli in a natural environment both from a theoretical and experimental perspective? And how does this change if we consider mixtures of odorants?
For both topics, we will briefly summarize the underlying principles of physics and review the experimental and theoretical Neuroscience literature, focusing on the aspects that are relevant to animals’ behavior. We hope that by bringing the physical principles behind odor plume landscapes to the fore we can contribute to promoting a new generation of experiments and models.
Keywords: Olfaction, Odor stimuli, Physics, Chemistry, insect navigation, Fluidodynamic
Received: 19 Aug 2019;
Accepted: 04 Nov 2019.
Copyright: © 2019 Pannunzi and Nowotny. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Mario Pannunzi, University of Sussex, Brighton, United Kingdom, firstname.lastname@example.org