Summary of electrophysiological activity of single olfactory sensory neurons (OSNs) in Drosophila larvae.

Spontaneous activity = the activity of a single OSN in the second prior to each olfactory stimulation. Firing rate = the activity of a single OSN during 1 second stimulation with one of 19 odors. Min. and max. denote the minimum and maximum rates observed. Response above criterion = change in spike frequency above/below the probabilistic response criterion (a change of ±5 Hz during stimulation as compared to the spontaneous activity seen in that OSN in the 10 s prior to stimulation – see Materials and Methods). Absolute = absolute OSN activity during stimulation. Larvae with a single functional OSN were [OrX-Gal4/UAS-Orco ; Orco−/−], constructed following the protocol in [7]. Or33b and Or47a are co-expressed in the same neuron, so their data were pooled. To be certain that spontaneous activity was obtained from a functional OSN, a response to at least one odor had to be detected in that OSN. No responses were detected for Or22c, Or33a and Or82a, so there are no data for these three classes of OSN.