Pavlovian conditional vocalizations of the rat: a model system for analyzing the fear of pain

Presentation of a 6-s light conditional stimulus (CS) that overlapped with a 1-s tailshock unconditional stimulus (US) generated audible conditional vocalization responses (VCRs) during the CS period. The rate of conditioning was observed to be directly related to the intensity of the tailshock US (0.15 mA-0.80 mA). The amplitude, duration, and number of VCRs was also directly related to US intensity, whereas the latency of VCRs from CS onset was inversely related to US intensity. VCRs were not observed in rats given explicitly unpaired presentations of CS and US (0.80 mA). The capacity of tailshock to support development of VCRs was found to depend on its capacity to elicit vocalization afterdischarges (VADs). Sonographic analysis of vocalizations revealed that VCRs and VADs share spectrographic characteristics. Results are discussed in terms of VCRs' providing a model system for analyzing the fear of pain and its suppression.