Qualitative and quantitative odour discrimation by mitral cells as compared to anterior olfactory nucleus cells

The responses to odour stimulation of 61 single mitral cells and of 64 single anterior olfactory nucleus (AON) units were simultaneously recorded from rabbits. The test battery consisted of 6 chemical stimuli delivered at two intensity levels corresponding to a hundred-fold difference in concentration. The odour discrimination reaches its best for the mitral cells stimulated weakly; it decreased somewhere when the same cells are stimulated strongly. At AON level the odour discrimination already limited in the case of weak stimuli, almost disappears for strong stimuli. Multidimensional analysis of the odour similarities, respectively in the olfactory bulb and the AON, reveals an unexpectedly high loading of the first axis with an intensity factor. Our results indicate that the discriminatory ability in the mitral cells and in the AON cells are respectively better and poorer than in the chemoreceptors.