Fig. 2
From: Behavioral and cognitive animal models in headache research
Demonstration of ultrasonic vocalisation (USV) calls in an awake rat following a cortical spreading depression. Emission of USV calls in the 22–27 kHz range in adult rats indicate a negative affective state such as pain or distress. The shift in the frequency at the beginning and at the end of the ultrasonic vocalisation is the typical feature of a biological sound