Optical imaging of odour-evoked activity in the projection neurons of the ant Camponotus fellah. A) Z-projection of a confocal stack of the left and right antennal lobes of a worker ant showing the anatomical features accessible to optical imaging. The frontal side of the antennal lobe presents on average 46 glomeruli arranged according to 4 clusters. Cluster arrangement is symmetrical between brain hemispheres. B) Example of calcium signals from the projection neurons in the antennal lobe of a worker ant. Odour-evoked activity is superimposed on a wide-field image of the lobe, using a false-colour code, ranging from just above baseline (dark violet, +0.1% ΔR) up to maximal activation (red, +1.5% ΔR). Two stimulations with each odour and the air control show the reproducibility of the calcium signals. Squares with numbers 1 to 3 relate to different classes after the cluster analysis presented in figure 3A. C) Standard right antennal lobe of C. fellah workers in a relative coordinate system, showing the average borders of the different glomerular clusters (anatomical preparations, n = 16 lobes). The inset indicates the numbers given to each cluster (see A). Colour squares correspond to the active spots identified in 7 ants which showed reproducible calcium signals. Most active spots were recorded in the two caudal clusters 1 and 2.