Odors appear to be represented in the antennal lobe of the locust by odor-specific, but overlapping, evolving assemblies of synchronously firing projection neurons. These projection neurons (PNs) fire in temporal patterns which are odor- and cell-specific. We have examined the variability of the responses of these cells across repeated stimulus presentations of the same odor. We found strong correlations (p<0.001) between the variability of spike trains of some, but not all, simultaneously recorded pairs of PNs. In some of these pairs, the firing of the neurons was negatively correlated: i.e. one neuron fired less than on average on trials when the other neuron fired more than on average. In other pairs, the firing was positively correlated. The correlation in some cell pairs was odor-evoked, and, interestingly, happened only at a particular epoche in the dynamically evolving response. We also observed significant correlations during periods of no odor stimulation, which disappeared at the onset of the odor responses. In addition, the inter-trial variability of the responses appeared to decrease in successive trials, making later responses more stereotyped. When the variability of the responses was analyzed as a function of time in the trial ¾ assessed as the variance in the firing rate for short time windows ¾ the variability appeared to vary systematically as the response evolved in time, so that a given cell would exhibit periods of high variability and periods of low variability. These results suggest that the effective connectivity of the antennal lobe varies as the response to odors unfolds in time, consistent with previous physiological findings showing the dynamical nature of the assemblies that represent odors. Supported by a Sloan Center for Theoretical Neurobiology Fellowship to A.B. and a PFF award to G.L.