Publication Date


Document Type


First Advisor

Coover, Gary D.

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Psychology


Fear; Emotional conditioning; Hippocampus (Brain)--Wounds and injuries


In Pavlovian delay conditioning, a conditioned stimulus (CS) overlaps and co-terminates with an unconditioned stimulus (US), such as foot shock, whereas in trace conditioning, CS offset occurs before onset of the US. One measure of conditioned fear that has been used to identify the neural substrates associated with learned fear is the fear-potentiated startle (FPS) reflex. Delay fear conditioning studies have revealed a critical role for the amygdala in fear learning and memory, whereas trace conditioning has revealed a critical role for the hippocampus. FPS has only recently been used to examine the neural systems and temporal characteristics involved in trace fear conditioning and the timing of fear expression. These experiments were designed to evaluate the temporal dynamics and neural substrates involved in trace-conditioned FPS. Experiment 1 examined the effects of variables that influence the magnitude of conditioned fear, including (1) the duration of the trace interval, (2) CS modality, and (3) the training to testing interval, on the magnitude and time course of fear expression. Experiment 2 compared the effects of NMDA lesions to the dorsal hippocampus (DH) or ventral hippocampus (VH) on acquisition and expression of trace FPS. The results of experiment I indicated that a light CS, but not a noise CS, resulted in a post-CS enhancement of FPS during the middle of the trace interval. A similar post-CS enhancement of FPS was also seen in subjects tested 1 day after training that was not demonstrated by subjects tested 7 days after training. There was very little evidence for inhibition of delay during the trace interval, and trace conditioning was greater when short trace intervals were used compared to longer trace intervals. In experiment 2, pre-training and post-training lesions of the DH or VH impaired acquisition and expression of trace FPS around the trace interval. In contrast, VH lesions, but not DH lesions, also reduced FPS to the CS. These results support prior studies indicating a role for the hippocampus in trace conditioning, and these results further suggest that the VH has a greater role in trace-conditioned fear compared to the DH.


Includes bibliographical references (pages [101]-117).


v, 118 pages




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