Neural mechanisms of ranging are different in two species of bats

The primary cue for ranging by echolocation is the delay between an emitted pulse and its echo. The abilities of several species of bats to discriminate target ranges have been accounted for by a theory which assumes that bats perform cross-correlation analysis of the FM components of pulse and echo. In this study, the neural mechanisms performing the cross-correlation are shown to differ in two species. The mustached bat emits CF-FM pulses with four harmonics (CF1-4 and FM1-4) while the little brown bat emits FM pulses with only one harmonic (FM1). In the auditory cortex of both species, there is a cluster or clusters of delay-tuned neurons. Delay-tuned neurons in the mustached bat utilize delay lines created by neurons which respond to the FM1 component of the pulse and extract range information from the combination of the pulse FM1 and the echo FMn (n = 2, 3, or 4). In contrast, delay-tuned neurons in the little brown bat utilize delay lines evoked by the pulse FM1, which is stronger than the echo FM1, and extract range information from the combination of the pulse FM1 and the echo FM1. Inhibition is involved in creating the delay lines in both species.