Toward an Estimate of the Number of Receptor Neuron Spikes Needed for Odor Identification

We measured the concentration dependence of the ability of rats to identify odorants and compared these results with the calcium signals in the nerve terminals of the olfactory receptor neurons. Odorant identification remained far above random chance at all concentrations tested (between 0.0006% and 35% of saturated vapor). In contrast the calcium signals were much smaller than their maximum values at odorant concentrations less than 1% of saturated vapor. Extrapolation suggests that only a few spikes in olfactory sensory neurons may be sufficient for correct odorant identification.