Perceptual stability during dramatic changes in olfactory bulb activation maps and dramatic declines in activation amplitudes

We compared the concentration dependence of the ability of rats to identify odorants with the calcium signals in the nerve terminals of the olfactory receptor neurons. Although identification performance decreased with concentrations both above and below the training stimuli it remained well above random at all concentrations tested (between 0.0006% and 35% of saturated vapor). In contrast, the calcium signals in the same awake animals were much smaller than their maximum values at odorant concentrations 1000 times smaller than the response at saturating odorant concentrations. We speculate that only a few spikes in olfactory sensory neurons may be sufficient for correct odorant identification.