Odorants are detected by receptor neurons (ORNs) that project to the antennal lobe (AL), the first olfactory neuropil in the brain. Once in the AL, ORNs make synaptic contacts with: i) projection interneurons (PNs), the first olfactory neurons that send olfactory information to the rest of the brain; and ii) local neurons (LNs) that form a dense network of lateral interactions within the AL. Anatomical and functional studies indicate that this network redistributes sensory information, presumably to enhance encoding of meaningful odors. To study the role of GABAergic interactions in the local processing of odors in Drosophila sp, we performed calcium imaging experiments of pure odorants and their mixtures. The difference between the activity patterns elicited by the mixtures and that expected based on the activity elicited by the components uncovered several asymmetrical lateral inhibitions. By blocking the expression of GABA-A receptors in PNs, we revealed the pattern of activity that the mixture should evoke if the inhibitory interactions were absent. Interestingly, the measured activity patterns fulfill the expected features of a functional code, however the comparison among pure odorants and mixtures uncovers different lateral interactions, presumably based on other inhibitory mechanisms that compensate the lack of GABA-A receptors. These results are consistent with a model in which the local AL network is established by experience and homeostasis dependent plasticity.