Odors elicit spatio-temporal patterns of activity in the brain. For several odorants and receptor types the ORN response dynamics normalized by the peak response are impartial of stimulus intensity for a large portion of the neuron’s dynamic range. Adaptation to a background odor changes the gain and dynamic range of the response but does not impact normalized response dynamics. Stimulating ORNs with BMN673 numerous odorants reveals significant odor-dependent delays in the ORN response functions. These differences however can be dominated by differences in stimulus dynamics. In one case the response of one ORN to two odorants is usually predicted solely from measurements of the odor signals. Within a large portion of their dynamic range ORNs can capture information about stimulus dynamics independently from intensity while introducing odor-dependent delays. How insects might use odor-specific stimulus dynamics and ORN BMN673 dynamics in discrimination and navigation tasks remains an open question. Introduction Insects and vertebrates ORNs project to segregated regions of the brain called glomeruli where they make synaptic connections with second-order neurons according to the odorant receptor (OR) they express (Su et al. 2009 Most odorants elicit distinct patterns of activity in the population of ORNs and in the glomeruli MAT1 suggesting that odors are encoded in spatial combinatorial maps (Malnic et al. 1999 Duchamp-Viret et al. 2000 Hallem and Carlson 2006 In locusts flies and moths odor evoked firing patterns are organized not only in space but also in time (Stopfer et al. 2003 Daly et al. 2004 Lei BMN673 et al. 2004 Wilson et al. 2004 Fruit flies with only one functional class of ORNs can discriminate between odors (DasGupta and Waddell 2008 These and other studies in vertebrates (Mozell 1964 Friedrich and Laurent 2001 Spors et al. 2006 Schaefer and Margrie 2007 Junek et al. 2010 Smear et al. 2011 suggested that information about odor stimuli might be encoded in temporal patterns in addition to spatial patterns of neural activity. In the locust independent information about identity and intensity of odor stimuli can be extracted from the analysis of spatio-temporal patterns of activity of projection neurons (PNs the neural targets of ORN) (Stopfer et al. 2003 even in presence of temporally structured stimuli (Brown et al. 2005 Temporally diverse PN responses likely originate from temporally diverse ORN responses (Raman et al. 2010 raising the question of what determines the dynamics of the ORN responses. In ((Fig. 1 ? 3 3 ? 5 as described in (de Bruyne et al. 2001 50 of odor dilution were placed in a paper filter contained in a Pasteur pipette; a 3-way solenoid valve redirected an air stream (3ml/sec) through the pipette which was manually placed into a hole on the side of the main delivery tube where a clean air stream (30ml/sec) was continuously running (Fig. 1A). This set up allows the delivery of multiple concentrations of odor on the same neuron. BMN673 When the PID was not used the main air stream was humidified by passing it through a bottle containing distilled water. (Fig. 7 ? 8 8 ? 9 20 of odor dilution were placed in a bottle (100ml). A small 3-way solenoid valve (The Lee Company) was placed in a hole on the side of the main delivery tube and was used to redirect the odor air stream from the exhaust to the delivery tube. Before starting recordings the odor bottle was placed in the set up for 10-15 minutes to let the odor gas phase reach equilibrium. We used a magnetic stirrer to facilitate equilibration of the liquid phase preparation. A new solenoid valve was used for each odor. (Fig. 4): a constant background was delivered through the bottle into the main air stream and puffs of increasing concentration were delivered through the Pasteur pipette as described BMN673 above. Note that odor dilutions prepared in the Pasteur pipette BMN673 do not result in the same gas phase concentration as odor dilution prepared in the bottle. For methyl butyrate the secondary air stream was 3ml/sec and different background intensities were obtained with different dilutions of odor in.