Reliable coding of small, behaviourally relevant interaural intensity differences in a pair of interneurons of an insect.

Insects, as vertebrates and humans, use interaural intensity differences (IIDs) between the two ears for sound localization. They are remarkably sensitive for small IIDs of the order of 1-2dB. Here, we investigated, using an independent ear stimulation paradigm, how such small IIDs are reliably encoded in the binaural discharge differences of a prominent pair of interneurons. Starting with an IID of 1dB, these differences are large and significant, with the louder side being more strongly excited. In a comparison of simultaneous responses of left and right interneurons, more than 70 and 90 per cent correct responses occur at IIDs of 1 and 2.5dB, respectively.