Figure S1: Temporally simple stimuli elicit relatively simple responses from PNs. a) Olfactory receptor neurons transduce chemical stimuli into electrical neural signals and relay their output to the antennal lobe (AL, in insects) or the olfactory bulb (OB, in vertebrates). Responses to odors are shaped in the AL (and OB) through interactions among the receptor output and two intrinsic neuron types: the excitatory principle neurons (PNs in insects, mitral/tufted cells in vertebrates) and inhibitory local neurons (LNs in insects, granule and other inhibitory juxtaglomerular neurons cells in vertebrates) and are then transmitted to higher brain centers. b) Recordings from a single locust PN reveal a rich repertoire of repeatable and long-lasting spatiotemporal patterns in response to pulses (brown bar, 1s; 3 different odors, 7 trials each, first shown as intracellular current trace (cal bar: 60mV), others as rasters). c) Regardless of stimulus intensity, PNs responded simply and variably to electrical square pulses (brown bars, 1s) delivered to the antenna nerve. These responses never outlasted the stimulus. d) PN response motifs induced by electrical (right) or odor (left) stimulation (brown bars). Responses (35 PNs in 7 experiments 96 PN-odor combinations, 200ms time bins) were coded as follows: white= excitatory; black=inhibitory; gray=no responses; see Materials and Methods. e) Odors, but not electrical stimuli, induced multi-phasic responses in PNs. Percentage of non-contiguous response phases (see Materials and Methods) evoked by electrical stimuli (blue) or odors (red); only PNs with two or more response transitions were included.

Geraniol

Hexanol

Octanol

Trans-2-hexen-1-ol

Hexanal

OCT100OCT10

OCT1

1sec

B

A

4sec

ORNb#123456789

1011121314

C

1sec

Figure S2: ORN firing patterns are not temporally heterogeneous. a) Different odorants evoked very similar electroantennogram (EAG) response profiles in vivo. Examples of EAG responses for five odorants: Geraniol; Hexanol; Octanol; Trans-2-hexen-1-ol; and Hexanal. Brown bar: odor pulse. b) An ORN can respond with different timing to different concentrations of an odor; responses of one ORN to three concentrations of Octanol are shown. c) Same results shown in Figure 1b, but here replotted to emphasize differences in response latency evoked by different odors.

Figure S3: Odor separabiity and convergence ratio. Odor separability by the PN ensemble declined gradually as more ORN types were integrated to generate the AL input. In Drosophila and mice, multiple copies of a single type of ORN converge upon each glomerulus. In locusts, though, the degree of convergence is not known. This analysis (see Materials and Methods) shows our model is robust to a range of convergence ratios.

Figure S4: Antennal lobe patterning requires temporally heterogeneous ORN firings. a) Distance of mean ORN and PN activity of each odor from the mean baseline response over time. The brown bar indicates the odor delivery period. b) Rate of change of mean ORN and PN ensemble activity for each odor over time. Again, the brown bar indicates the odor delivery period.

Figure S5: GABAA type inhibition is required for generating odor-evoked oscillations in the model antennal lobe, as previously shown (MacLeod and Laurent, 1996; Bazhenov et al., 2001b). a1) In our model, odor-evoked LFP oscillations were abolished when GABAA type fast inhibitory currents from LNs were removed. a2) LFP power spectrum for model without GABAA inhibition reveals no regular oscillatory activity. b) Crosscorrelogram of PN and LN subthreshold activity with the LFP in the model AL without GABAA inhibition. c1, c2, d show parallel results when only GABAB type inhibition was removed from the model.

Figure S6: Locust sensilla contained multiple ORNs, thus single-electrode extracellular recordings of their activity required spike sorting. Example of ORN spike sorting using the Spike-o-Matic algorithm; see Materials and Methods. (Using more than one electrode did not improve sorting quality.) a) Raw extracellular trace showing responses of multiple ORNs within a single sensillum; B) Inter-spike interval distribution of different sorted units. C) Comparison of ORN waveforms; Unit waveforms differed both in their response amplitude and shape, d,e) Individual events (black), their mean (red), and the SD (gray; clipped portion reflects variability in spike amplitude caused by sensory adaptation) in a recording channel for all events belonging to two different ORNs. f ) Histograms obtained by projecting high-dimensional ORN event representations onto the line connecting their means. To be judged well-separated, as in this case, cluster centers had to be at least five times the noise SD apart.

Figure S7: Example of PN spike sorting. a) Individual events (black), their mean (red), and the SD (gray) in each of the four channels for all events classified as PN2 and PN3. b) Histograms obtained by projecting high-dimensional PN1 and PN2 events onto the line connecting their means. To be judged well-separated, as in this case, cluster centers must be separated by at least five times the noise SD.