Cover picture: Three odorant maps detected in vivo by optical imaging of the mouse olfactory bulbs, depicted as 3D peaks of activity [red (high) to white (low)], superimposed on a blood vessel map of the dorsal surface of the bulbs. These maps illustrate the odorant responses to two individual aldehydes and a simple binary mixture. The top map shows the olfactory bulb response to propanal, the middle map shows the response to butanal, and the bottom map shows the response to a 1:1 mixture of each, demonstrating that for these two molecules, the mixture-induced activity map is a spatial combination of the two individual component maps. For details, see the article by Belluscio and Katz in the issue (pages 2113-2122).