Fig. 1. Simultaneously recorded activity of two co-located olfactory receptor neurones. Differences in action potential (spike) amplitude allow for separation of activity. Stimulation with a blank results in no increased activity from any of the neurones. Stimulation with ethyl 3-hydroxybutyrate elicits a strong response from the smaller spiking neurone, indicated by `B' (neurone later classified as S2B), whereas the larger spiking neurone, indicated by `A' is unaffected by the stimulus. Boxed area shows an expanded part of the recording. Horizontal bar indicates stimulus duration, 0.5 s.