In laboratory rats, what ultrasonic vocalizations are strongly associated with positive social interactions?

In laboratory rats, 50-kHz ultrasonic vocalizations are strongly associated with positive social interactions. Rats produce these sounds above the normal human hearing range, so people cannot hear them without specialized equipment.

Researchers commonly record 50-kHz calls during play, gentle handling, mating-related behavior, and anticipation of rewards. The calls are not one completely uniform sound: scientists have identified several subtypes with different acoustic patterns and behavioral contexts. Their presence generally indicates positive arousal, although interpretation depends on the situation.

Rats also produce lower-frequency ultrasonic calls, especially around 22 kHz, in contexts linked with fear, distress, or negative experiences. This creates a useful but simplified contrast: 50-kHz calls are often associated with positive states, while 22-kHz calls are often associated with aversive states. The exact meaning of a call should still be interpreted alongside the animal’s behavior and surroundings.