Fig. 3. Examples of recordings from receptor neurons showing spontaneous activity and responses of olfactory stimuli. (A) Spontaneous activity of two ORNs co-located in a short blunt type II trichoid sensillum, sbtII-2. (B) Inset showing 0.1 s of the spontaneous activity at higher resolution. Differences in spike amplitudes allow separation of two neurons, i.e. A (larger spikes) and B (smaller spikes). (C) Sensitivity of the neurons to the feet headspace extract was first tested by puffing it over the sensillum. (D) Stimulation of the sbtII-2A cell with 0.1% octanal, identified through GC–MS analyses of the feet headspace extract, elicited an excitatory response. (E) Expanded view of the response to octanal. Horizontal scale bars: 0.5 s odor stimulation. For the blank test we used paraffin oil only.