Fear conditioned discrimination of frequency modulated sweeps within species-specific calls of mustached bats.

Jie Ma,Jagmeet S Kanwal,Robert T Naumann

doi:10.1371/journal.pone.0010579

Abstract

Social and echolocation vocalizations of bats contain different patterns of frequency modulations. An adult bat's ability to discriminate between various FM parameters, however, is not well established. Using changes in heart rate (HR) as a quantitative measure of associative learning, we demonstrate that mustached bats (Pteronotus parnellii) can be fear conditioned to linear frequency modulated (FM) sweeps typically centered at their acoustic fovea (∼60 kHz). We also show that HR is sensitive to a change in the direction of the conditional frequency modulation keeping all other parameters constant. In addition, a change in either depth or duration co-varied with FM rate is reflected in the change in HR. Finally, HR increases linearly with FM rate incremented by 0.1 kHz/ms from a pure tone to a target rate of 1.0 kHz/ms of the conditional stimulus. Learning is relatively rapid, occurring after a single training session. We also observed that fear conditioning enhances local field potential activity within the basolateral amygdala. Neural response enhancement coinciding with rapid learning and a fine scale cortical representation of FM sweeps shown earlier make FMs prime candidates for discriminating between different call types and possibly communicating socially relevant information within species-specific sounds.

Highlights

Recognition of complex sounds and discrimination between variations in their acoustic components is vital for social interactions in a highly social and vocal species
We know from Morton’s motivation-structure hypothesis that different types of sound patterns, including frequency modulated (FM) have a universal significance in avian and mammalian species [1]. Such discriminatory capabilities could be meaningful during echolocation, given that a small modulation of the constant frequency (CF) can occur within the Doppler-shifted echo returning from targets during the search phase of echolocation behavior in this species
Calculations show that upward FMs with slow rates (,0.01 kHz/ ms) can be generated for the second harmonic of the Dopplershifted echo CF if the bat accelerates and turns directly towards a target (Mueller, R., personal communication)

Summary

Introduction

Recognition of complex sounds and discrimination between variations in their acoustic components is vital for social interactions in a highly social and vocal species. Behavioral and/or neurophysiological studies on the acoustic basis of recognition of species-specific calls involve time and labor-intensive acquisition of a sometimes-large set of speciesspecific sounds. An analysis of their acoustic organization reveals the presence of both spectral and temporal acoustic features [6]. Some acoustic features, such as the pitch of a sound, can convey information about the mood, size and/or identity (including sex and social status) of the emitter [13,14,15]. Mongolian gerbils (Meriones unguiculatus) can discriminate between different directions of FM sweeps [16] and rats (Rattus norvegicus) can categorize FM sweeps based on either the direction or rate of modulation [17]

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Conclusion