The second experiment was made to record effects of lesions of different brain parts, which were amygdala, dorsal hippocampus, and cortex dorsal to the hippocampus. It was revealed that animals with amygdala lesions showed a significant difference in both pre-CS and CS during the experiment. Animals with lesions on hippocampus showed no significant change in time of freezing during the CS on any day but did show a significantly reduced freezing time during pre-CS condition. Lesions of the neocortex above the hippocampus had no obvious change on freezing to neither CS nor pre-CS compared with unoperated control group (Phillips R. G. and LeDoux, 1992, p.276).This study indicates that amygdala is an essential component in fear conditioning, regardless of the type of stimulus input serving as the CS. Amygdala is involved in the formation of associations between the aversive US and of any of a variety of types of CSS, ranging from the simplest to the most complex. Hippocampus, although not necessary for conditioning with an explicit CS, is necessary for the conditioning of fear responses to contextual stimuli. Also, the study indicates the contextual conditioning may not be a necessary aspect of fear conditioning. I agree with, it because when intensities of the US are low, conditioning only developed to the explicit CS. When intensities increases, freezing time increases in the both explicit CS and the context, but contextual conditioning required a greater number of exposures to the US.