Conditioned Fear
Conditioned Fear: This is a test of amygdala function. In basic fear conditioning, the animal is placed in a test chamber and exposed to a tone followed by a mild foot shock. This is repeated several times. At a specified later time (usually 24 h) the animal is returned to the chamber and baseline activity is recorded, then the tone re-presented without foot shock. Time spent freezing relative to the baseline represents the conditioned response to the tone. In cued-contextual fear conditioning, initial conditioning is as described above but the test phase is different. On day-2 of the test, the animal is first returned to the original chamber and tested for 5 min. Amount of freezing is used as the measure of contextual fear conditioning since the animal is responding to its surroundings rather than to the tone. One h later the animal is placed in a second chamber that is distinct in texture from the original and the animal is scored for freezing for 3 min to establish a baseline in the new context. Then the tone is presented and freezing scored for the next 3 min. Freezing in this environment is scored and compared to the pre-tone behavior and the increase in freezing after the tone is an index of cued conditioning. Cued conditioning is mediated primarily by the amygdala whereas contextual conditioning is mediated by the hippocampus, subiculum, cingulate, prefrontal and perirhinal cortices.
