Journal
NEUROBIOLOGY OF LEARNING AND MEMORY
Volume 183, Issue -, Pages -Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.nlm.2021.107485
Keywords
Second-order conditioning; Fear conditioning; Context fear; Basolateral amygdala
Funding
- Australian Research Council [DP170103952]
- ARC Australia
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Studies investigating second-order fear conditioning using complex stimuli such as contexts found that neuronal activity in the basolateral amygdala is essential for the acquisition and extinction of fear. The second-order fear can be reduced through extinction of its first-order conditioned stimulus associate, but it can be restored when fear of the first-order stimulus spontaneously recovers or is reconditioned.
Second-order fear conditioning has been demonstrated in protocols using discrete and simple stimuli, and much is now known about its behavioral and neural characteristics. In contrast, the mechanisms of second-order conditioning to more complex stimuli, such as contexts, are unknown. To address this gap in our knowledge, we conducted a series of experiments to investigate the neural and behavioral characteristics of second-order context fear conditioning in rats. We found that rats acquire fear to a context in which a first-order conditioned stimulus is presented (Experiment 1); neuronal activity in the basolateral amygdala (BLA) is required for the acquisition (Experiment 2) and extinction (Experiment 3) of second-order context fear; second-order context fear can be reduced by extinction of its first-order conditioned stimulus associate (Experiment 4); and that second-order fear reduced in this way is restored when fear of the first-order conditioned stimulus spontaneously recovers or is reconditioned (Experiment 5). Thus, second-order context fear requires neuronal activity in the BLA, and once established, tracks the level of fear to its first-order conditioned stimulus-associate. These results are discussed with respect to the substrates of second-order fear conditioning in other protocols, and the role of the amygdala in different forms of conditioning.
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