The Neural Processing of Frequency Modulations in the Auditory System of Bats

Abstract

Bats rely to an inordinate degree on sound for survival. Bats, of course, are best known for their ability to echolocate, a form of biosonar used for both orientation and detecting, identifying, and capturing prey. Not only do they rely on hearing for orientation and hunting through echolocation, but hearing is also critically impor-tant for social communication. Many bats live in large colonies where they engage in a myriad of social interactions that are accomplished almost entirely with sound since they live in dark environments where visual displays are of no use (Griffi n 1958). Their communication signals can be quite elaborate (Bohn et al. 2009), and some species are capable of vocal learning (Boughman 1998 ; Knornschild et al. 2006). Indeed, the repertoire of signals bats use for vocal communication is rich and sophisticated (Kanwal 1999 ; Bohn et al. 2008). This chapter is concerned with the neural processing of signals that bats employ in both their echolocation and communication calls. Particular attention is given to the processing of communication calls and the roles of inhibition in creating response selectivity that enables the auditory system to distinguish among the various signals bats receive. Vocal communication was presumably used by their ancestors before bats took to the night sky to exploit a food supply for which there was little competition. It is noteworthy in this regard that the pri-mary acoustic feature of virtually all echolocation calls is a brief, frequency-modulated (FM) sweep (Simmons et al. 1975 ; Neuweiler 1990); strikingly similar FM sweeps are also acoustic features of many communication calls emitted by bats (Schwartz et al. 2007 ; Bohn et al. 2008). Thus, the view presented in this