Chapter 7 - Processing of Ultrasonic Vocalizations in the Auditory Midbrain of Mice

Abstract

Abstract Mice have become an important species for understanding how complex sounds such as vocalizations or speech are processed by the auditory system. This is possible because mice have a typical mammalian auditory system and extensively use vocalizations during social behaviors. This chapter focuses on our current understanding of the encoding of mouse ultrasonic vocalizations by the auditory midbrain. Historically, encoding of vocalizations was thought to be a cortical process. However, recent evidence clearly indicates that selectivity to vocalizations emerges at least at the level of the auditory midbrain and possibly even at lower brainstem levels. The mechanisms by which auditory midbrain neurons encode mouse ultrasonic vocalizations are described in this chapter. Neural selectivity to vocalizations is driven by the complex interplay between excitatory and inhibitory inputs to auditory midbrain neurons. In addition, ultrasonic mouse vocalizations create low frequency distortion products on the cochlea; the auditory system exploits this to allow neurons with low-frequency response areas to encode high frequency vocalizations. The use of distortion products has allowed mice (and maybe other rodents) to communicate with ultrasonic signals without evolving specializations in the cochlea that subserve high-frequency hearing.