While fear can be adaptive by inhibiting pain and eliciting defensive behavior, long lasting fear can have negative effects on overall health, including psychological disorders, such as PTSD (Harris & Seckl, 2011; Bolles & Fanselow, 1980). Unpredictability of an aversive event can sensitize the fear circuitry causing an increase in one’s stress response later in life (Davis et al., 2010; Quinn et al., 2013). Past research has shown that rats prefer predictable shocks to unpredictable shocks (Badia et al., 1979). When looking at the physiological effects of shocks on rats, it was shown that predictable shocks can be more stressful than unpredictable shocks when the sessions are long or severe; however, unpredictable conditions are more stressful when experienced short term (Abbot et al., 1984). In this study, 48 Long-Evans rats were assigned to one of three conditions: cued-shock (15FS-cued), shock (15FS), and no shock (0FS) during a single, acute stressful event. The cued-shock condition was thought to make the aversive stimulus more predictable thus allowing for the endogenous analgesic system to be activated when the cue occurred (Fanselow & Bolles, 1979). The reduction of pain caused by the release of endorphins when the tone preceded the footshock was predicted to reduce the enhancement of fear in adulthood. We hypothesize that the 0FS animals will freeze less than both the 15FS and 15FS-cued conditions. We also predict that when the footshocks are cued with a tone during fear conditioning in infancy, freezing behavior will be less in comparison to those who received the footshocks without the cue. Results revealed that 15FS animals froze at higher levels than the animals that received 0 footshocks. However, the 15FS-cued condition did not differ from the 0FS or the 15FS condition. In other words, there was a modest effect of the cueing during infancy on the stress-enhancement of fear learning in later adulthood.
Author: Sarah M. Reitz
Faculty Advisor: Jennifer J. Quinn, Psychology
Graduate Student Advisor: Brianna L. Minshall, Psychology
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