The midbrain creates and the thalamus sharpens echo-delay tuning for the cortical representation of target-distance information in the mustached bat.

Mustached bats emit complex biosonar 'pulses' for echolocation. A delay of an echo from the emitted pulse carries target-distance information. At the auditory periphery, distance information is expressed by a time interval between the responses of neurons to the emitted pulse and its echo. In the auditory cortex (AC), however, it is mapped by 'FM-FM' neurons which are tuned to particular echo delays. FM-FM neurons have been found not only in the AC but also in the inferior colliculus (IC) of the midbrain and the medial geniculate body (MGB) of the thalamus. In the present study, we found that the IC has a precursor of the cortical echo-delay axis for the systematic representation of target-distance information and that the MGB shows the improved neural representation of target-distance information.