Auditory midbrain neurons that count

Many acoustic communication signals, including human speech and music, consist of a precise temporal arrangement of discrete elements, but it is unclear whether this precise temporal patterning is required to activate the sensory neurons that mediate signal recognition. In a variety of systems, neurons respond selectively when two1,2,3 or more4 sound elements are presented in a particular temporal order and the precise relative timing of these elements is particularly important for 'delay-tuned' neurons2, including 'tracking' types5, in bats. Here we show that one class of auditory neurons in the midbrain of anurans (frogs and toads) responds only to a series of specific interpulse intervals (IPIs); in the most selective cases, a single interval that is slightly longer or shorter than the requisite interval can reset this interval-counting process.