Increasing odorant concentrations cause an increase in the extent and levels of activity in the vertebrate olfactory bulb and insect antennal lobe as measured with calcium imaging. Such responses have sometimes been attributed to input from receptors. In contrast, responses of mitral cells to increasing odor concentration have traditionally presented a less clear picture, with non-monotonic changes in firing rate. How are these pictures of input & output reconciled? We recorded intracellularly from projection neurons (PNs), analogs of mitral cells in the locust antennal lobe, and show that the mean firing rate across PNs is relatively invariant to odor concentration, due to a dynamic balance of excitation and inhibition acting as a gain control mechanism: as odor concentration increases, inhibition is strengthened in parallel to excitation. This effect, which is missed by many imaging techniques, reduces the dynamic range of PN output and may contribute to the fact that complex odor blends do not evoke the percepts corresponding to all of their components, but rather a different percept altogether, despite the fact that receptors’ responses are monotonic in concentration: the increase of inhibition with increasing concentration allows PNs to be inhibited with additional blend components, allowing cells to be tuned to particular odor components. In contrast to firing rates, synchronization increases monotonically with increasing odorant concentration, and its dependence on concentration is not reduced by priming of PN responses (see Bäcker and Laurent, 2000).