Figure 1. Types of rat ultrasonic vocalizations (USV). A, Isolation-induced 40-kHz USV emitted by an 11-day-old male Wistar rat after separation from mother and littermates. B, Low-frequency 22-kHz USV emitted by a 3-month-old male Wistar rat during fear conditioning. C, High-frequency 50-kHz USV emitted by a 3-month-old male Wistar rat searching for conspecifics.
