Abstract
Rats can acquire fear by observing conspecifics that express fear in the presence of conditioned fear stimuli. This process is called observational fear learning and is based on the social transmission of the demonstrator rat’s emotion and the induction of an empathy-like or anxiety state in the observer. The aim of the present study was to investigate the role of trait anxiety and ultrasonic vocalization in observational fear learning. Two experiments with male Wistar rats were performed. In the first experiment, trait anxiety was assessed in a light–dark box test before the rats were submitted to the observational fear learning procedure. In the second experiment, ultrasonic vocalization was recorded throughout the whole observational fear learning procedure, and 22 kHz and 50 kHz calls were analyzed. The results of our study show that trait anxiety differently affects direct fear learning and observational fear learning. Direct fear learning was more pronounced with higher trait anxiety, while observational fear learning was the best with a medium-level of trait anxiety. There were no indications in the present study that ultrasonic vocalization, especially emission of 22 kHz calls, but also 50 kHz calls, are critical for observational fear learning.
Highlights
In potentially threatening situations, rats—as other animals and humans—express a variety of defensive behavior that helps to survive such situations [1]
After grouping the observational fear learning sessions-in-sessions with low (0–1), medium (21–121), and high number (215–590) of 22 kHz calls, we found that the number of 22 kHz calls in the observational fear learning sessions affected the freezing behavior of DEM rats in the retention test (Figure 3e; analysis of variance (ANOVA): F2,15 = 4.61, p = 0.03)
The present study investigated the role of trait anxiety and ultrasonic vocalization on observational fear learning in rats
Summary
Rats—as other animals and humans—express a variety of defensive behavior that helps to survive such situations [1]. After the initial defensive response, e.g., hiding or freezing, many rats emit ultrasonic vocalizations [1,4,5]. These calls are characterized by a peak frequency around 22 kHz, a narrow bandwidth, and call durations around one second [6,7]. The function of these 22 kHz calls is not completely understood. Only modest effects are reported in experiments using playbacks of natural 22 kHz calls [10,11,12,13], eventually questioning the direct behavioral effects of 22 kHz calls
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