Original Research ARTICLE

Front. Syst. Neurosci., 04 August 2008 | http://dx.doi.org/10.3389/neuro.06.003.2007

Odor concentration invariance by chemical ratio coding

Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA
Many animal species rely on chemical signals to extract ecologically important information from the environment. Yet in natural conditions chemical signals will frequently undergo concentration changes that produce differences in both level and pattern of activation of olfactory receptor neurons. Thus, a central problem in olfactory processing is how the system is able to recognize the same stimulus across different concentrations. To signal species identity for mate recognition, some insects use the ratio of two components in a binary chemical mixture to produce a code that is invariant to dilution. Here, using psychophysical methods, we show that rats also classify binary odor mixtures according to the molar ratios of their components, spontaneously generalizing over at least a tenfold concentration range. These results indicate that extracting chemical ratio information is not restricted to pheromone signaling and suggest a general solution for concentration-invariant odor recognition by the mammalian olfactory system.
olfaction, odor recognition, concentration-invariance, ratio
Uchida N and Mainen ZF (2008). Odor concentration invariance by chemical ratio coding. Front. Syst. Neurosci. 1:3. doi: 10.3389/neuro.06.003.2007
07 September 2007;
 Paper pending published:
26 November 2007;
25 March 2008;
 Published online:
08 April 2008.

Edited by:

Mriganka Sur, Massachusetts Institute of Technology, USA

Reviewed by:

Gilles Laurent, California Institute of Technology, USA
© 2008 Uchida and Mainen. This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.
Zachary F. Mainen, Champalimaud Neuroscience Program, Instituito Gulbenkian de Ciência, Rua Quinta Grande, 6 P-2780-156 Oeiras, Portugal. e-mail: zmainen@igc.gulbenkian.pt