Encoding of Ultrasonic Communication Signals in Rat Auditory Cortex
All social animals require a means of communication, and for many species that need is filled by the use of vocalizations. While far less intricate than human speech, many animals employ systems of vocalizations in order to attract mates, convey information about the environment, or to express an emotional state. One such animal is the rat, which communicates via a set of ultra-sonic vocalizations (USVs) in the 50kHz frequency range. These USVs have a conveniently simple structure, making them easy to synthesize and modify. The rat thus provides an excellent model system with which to probe the processing and encoding of such communication signals in the mammalian brain. In the studies contained within this work we take several novel steps in the investigation of rat vocalizations, and in the study of auditory objects in general. We develop a novel system for parameterizing, purifying, and modifying rat USVs. We model neural responses to USVs, and show that a simple model based on frequency modulation outperforms a more traditional, spectral-based model. We study how neurons in the auditory cortex react to shifts in the statistical structure of USVs, and find evidence that the primary auditory cortex is specialized for the temporal structure of natural vocalizations. We go on to examine the degree to which neural representations of USVs are invariant to small transformations of the USVs, and find evidence that this invariance is greater in the higher brain area SRAF, than in the lower brain area A1. Finally, we develop and implement an experimental system that allows us to probe a rat's perception of a stimulus by examining the rat's behavioral reactions.
Networked Digital Library of Theses and Dissertations