Rat ultrasonic vocalizations: significance and mechanisms

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Rats appear largely silent to us, but they make many sounds beyond the human hearing range. These are termed ultrasonic vocalizations and are probably used for communication. By using specialized equipment, it is possible to eavesdrop on these inaudible calls. In this way, we have been able to discern more than a dozen types of vocalizations. Different kinds of vocalization are prevalent in different situations, suggesting that they may reflect different emotional states. For example, some evidence suggests that certain kinds of vocalization might indicate when a rat is experiencing positive emotion. The overall goal of this research is to better understand what these vocalizations signify and what happens in the brain when an animal vocalizes. To tackle the first question, we will start by exposing rats to different kinds of vocalizations, to see how this affects their behaviour. We will also test whether certain kinds of ultrasonic calls are made when rats are given drugs or other stimuli that are known to be rewarding. Rats often vocalize when they are expecting different kinds of reward, and we will determine whether there are corresponding types of call that reflect anticipation. Finally, in order to explore the brain mechanisms that underpin ultrasonic calling, we will record the release of a neurotransmitter called dopamine, which has been heavily implicated in reward processes in the brain. This research is at a fundamental stage, but in the longer term it could lead to several practical benefits. For example, if ultrasonic vocalizations do indeed reveal different emotional states, they could provide a useful and novel approach for studies linking brain activity to emotions such as pleasure and disappointment. It may also be possible to use specific types of ultrasonic vocalizations in order to screen for novel drug therapies for depression, chronic pain, and anxiety. Lastly, this basic research may one day lead to more effective methods for controlling rodent populations that ravage food supplies.