Neural representation of bisonar information in the auditory cortex of the mustached bat

Abstract

For echolocation, the mustached bat (Pteronotus parnellii rubiginosus) emits orientation sounds containing up to four harmonics, each of which consists of a long constant-frequency (CF) component followed by a short frequency-modulated (FM) component. The auditory system of this species extracts different types of bisonar information from complex orientation sound and echo pairs and represents these systematically in the separate areas of the cerebral cortex. Nine clusters of combination-sensitive neurons have thus far been found in the auditory cortex. Two of these clusters making up the CF/CF area consist of CF1/CF2 and CF1/CF3 facilitation neurons which are tuned to particular Doppler shifts, i.e., target velocities from 8 to −2 m/s. The remaining seven clusters consist of different types of FM-FM neurons which are tuned to particular echo delays, i.e., target distances. Three of these clusters, making up the FM-FM area, consist of FM1-FM2, FM1-FM3, and FM1-FM4 facilitation neurons. The FM-FM area projects bilaterally to the dorsal fringe (DF) and ventrolateral (VL) areas of the nonprimary auditory cortex. The DF area consists of three clusters of FM-FM facilitation neurons. The VL area contains a small cluster of facilitation neurons that are tuned only to the FM1-FM2 combination. The FM-FM area represents target distances from 7 to 310 era, while the DF area represents these from 14 to 140 cm. [Work supported by 1-R01-NS 17333.]