What the nose tells the brain about odors

Optical recording using calcium sensitive dyes was used to measure the input to the olfactory bulb from the nose. Because all of the receptor neurons projecting to one glomerulus in the bulb express the same receptor protein, the signal from each glomerulus represents the response properties of a single receptor protein. Individual receptors responded to a variety of odorants. In the mouse, the number of responding glomeruli increased with increasing odorant concentration. In the turtle the input maps for different odorant concentrations were similar; the signals were concentration invariant.