Rat 22-kHz ultrasonic vocalizations (USVs) are exhibited in response to a wide variety of stimuli. Recently, we have shown that, depending on the internal state of the animal, a given stimulus can either trigger aversive 22-kHz USVs or hedonic 50-kHz USVs. Notably, preexposure to reward/stress shifts this response of rats; we can selectively breed in a robust fashion for these differential responses. In addition, a change from hedonic 50-kHz to aversive 22-kHz USVs is typical during prolonged social interactions, which reflects a shift from initiation to approach, avoidance, and termination of behaviors; a similar pattern is seen with nonsocial stimuli. We now propose that 22-kHz USVs should not only be thought of as induced primarily by aversive stimuli but also by other stimuli as the transition from approach to avoidance for a wide variety of hedonic and aversive stimuli as well as a means to influence the refractory period for these motivated behaviors. A new model for motivated behavior is proposed in which changing the threshold for eliciting 50-kHz USVs as well as subsequent 22-kHz USVs and returning to baseline can account for the rhythm of changes in motivated behavior. Therefore, understanding the plasticity mechanisms in the neuronal circuits that underlie production of both 50-kHz USVs and 22-kHz USVs will elucidate processing of emotional behavior and decision making as well as lead to the development of potential therapeutics for psychiatric disorders.