Text

theses

ETD doctoral

The amygdala plays a critical role in mediating fear responses to a cue (CS) that was previously associated with danger (US) or to species-specific stimuli such as predators. However, for proper behavioral functioning, these defensive behavioral tendencies must, at times, be suppressed. For example, animals have to suppress fear responses elicited by the CS when the CS is presented repeatedly in the absence of the US, a process called extinction of conditioned fear responses. In addition, animals have evolved defensive strategies that minimize the likelihood of encounters with predators. However, in order to attain food, these defensive strategies must be suppressed. Intercalated (ITC) amygdala neurons are thought to play a critical role in the extinction of conditioned fear. However, we lack criteria to identify ITC cells in vivo and as a result, it has been impossible to test key predictions of ITC extinction models. Among these, it was predicted that ITC cells are strongly excited by infralimbic inputs, explaining why infralimbic inhibition interferes with extinction. In the first chapter, I found ITC cells are strongly responsive to infralimbic stimuli and their unique responses to infralimbic inputs constitute a reliable criterion to identify them in behaving animals. In addition, the amygdala regulates innate fear in a foraging task. In this task, rats had to leave a safe nest to retrieve food positioned at various distances from a robot predator. Intra-amygdala infusions of drugs that reduced or enhanced the activity of amygdala neurons respectively led to increases or decreases in risk-taking. While these findings indicate that the amygdala regulates innate fear responses, how it does so is unclear. To address this question, I recorded neurons in the basolateral nucleus while rats engaged in the foraging task. I found that the vast majority of projection cells became silent upon initiation of foraging. Last, by comparing the activity of BL cells during the foraging task with tasks that did not include explicit threats or rewards, we found that BL activity is best understood as reflecting a continuous evaluative process where internal states, reward availability, and threat determine whether rats will engage in a situation.

ETD_6610

doi:10.7282/T35B04HG

Ph.D.

Includes bibliographical references

by Alon Amir

The author owns the copyright to this work.