Figure 1. Adaptation and saturation modulate ORN responses to broadly distributed naturalistic stimuli.
(a) Ethyl acetate odorant (top) elicits LFP (middle) and firing rate (bottom) responses from a ab3A ORN. (b) 2-butanone odorant (top) elicits LFP (middle) and firing rate (bottom) responses from a ab2A ORN. Insets in (a–b) show pairs of whiffs and the LFP and firing rate responses they elicit on an expanded timescale. All pairs of insets are shown at the same scale, for 400 ms around a whiff. (c) ab2 LFP responses vs. projected stimulus. (d) ab2A firing rate vs. projected stimulus. (c) and (d) show that ORN responses differ significantly from linearity. (e) ab2 LFP responses vs. whiff amplitude. (f) ab2A firing rate vs. whiff amplitude. n = 15 trials from 2 ORNs. 101 whiffs shown in (e–f).
Figure 1—figure supplement 1. Diagram of odor delivery device and calibration of Photo-Ionization Detector (PID).
1 mL of pure odorant was placed in a 20 mL scintillation vial with a screw top. A computer-controlled Mass Flow Controller (MFC) forced air through this vial, which created an odorized airstream. This airstream was either directed into the main air flow or to waste (vacuum) using a solenoid valve. A PID (inlet needle at the outlet of the main air tube) recorded the gas phase concentration of the odorant stimulus as it was presented to the fly. We calibrated the PID by depleting a fixed, known volume of pure odorant at various flow rates, and integrating the resultant PID signal. Using the known densities and molar masses of these monomolecular odorants, we built maps from PID response in Volts onto the absolute odorant flux. This relationship was found to be linear for the two odorants tested.
Figure 1—figure supplement 2. Example of simultaneously acquired primary data (ab3A responses to ethyl acetate stimulus).
(a) Seven repetitions of fluctuating ethyl acetate stimulus (each gray trace is from a presentation to a different ab3A neuron in a different sensillum; mean shown in black). (b) Raw voltage recording from 7 different ab3 sensilla. (gray traces, one from each neuron; mean shown in black). (c) One of the traces in (b) is filtered to visualize spikes. Note that spikes from the ab3A neuron are typically larger than spikes from the ab3B neuron, enabling us to sort them and measure the response of a single neuron in vivo. (d) Raster of ab3A spikes for 7 different ORNs. Arrow indicates trace shown in (c).
Figure 1—figure supplement 3. Statistics of the ethyl acetate stimulus with naturalistic temporal structure.
(a) Distribution of whiff intensities. (b) Distribution of whiff durations. (c) Distribution of blank durations. Predicted distributions from Celani et al. (2014) are shown in red lines (a–c). is the odor concentration (whiff intensity). and are whiff and blank durations. (d) Mean vs. standard deviation of stimulus, computed in 400 ms non-overlapping blocks. (e) Correlation between mean and standard deviation of stimulus as a function of window length. Peak correlation observed for timescales ~400 ms. (f) Autocorrelation function of the stimulus. Shading indicates standard deviation across trials.
Figure 1—figure supplement 4. Deviations from linearity persist even when filters extracted from Gaussian stimuli are used to project naturalistic stimulus.
(a) LFP filters for ab2A ORNs responding to 2-butanone, extracted either form naturalistic stimuli (black) or from Gaussian stimuli (red). (b) LFP responses to naturalistic stimulus vs. stimulus projected through filter computed from naturalistic stimulus (Black filter in a). (c) LFP responses to naturalistic stimulus vs. stimulus projected through filter computed from Gaussian stimulus (red filter in a). (d) Firing rate filters for ab2A ORNs responding to 2-butanone, extracted either from naturalistic stimuli (black) or from Gaussian stimuli (red). (e) Firing rate responses vs. stimulus projected through filter computed from naturalistic stimulus (black filter in d). (f) Firing rate responses vs. stimulus projected through filter computed from Gaussian stimulus (red filter in d).