Neural Axis Representing Target Range in the Auditory Cortex of the Mustache Bat

In echolocating bats, the primary cue for determining distance to a target is the interval between an emitted orientation sound and its echo. Whereas frequency is represented by place in the bat cochlea, no anatomical location represents target range. Target range is coded by the time interval between grouped discharges of primary auditory neurons in response to both the emitted sound and its echo. In the frequency-modulated-signal processing area of the auditory cortex of the mustache bat ( Pteronotus parnellii rubiginosus ), neurons respond poorly or not at all to synthesized orientation sounds or echoes alone but respond vigorously to echoes following the emitted sound with a specific delay from targets at a specific range. These range-tuned neurons are systematically arranged along the rostrocaudal axis of the frequency-modulated-signal processing area according to the delays to which they best respond, and thus represent target range in terms of cortical organization. The frequency-modulated-signal processing area therefore shows odotopic representation.