Amygdala and Hippocampus - Essay Example

Article Review Reasons to conduct this study: The contextual CS and the cued CS is different. Although they have the same emotional responses, they have different processing pathways in brain. Amygdala has been always considered as an essential part in fear conditioning. Lesions of amygdala interfere with acquisitions and expression of emotional responses conditions to both cued and contextual CSs. Many studies see hippocampus as an important role in contextual processing. The main goal of this research to reexamine the role of the amygdala and to assess the possible contribution of the hippocampus to contextual fear conditioning as well as examining “the effects of lesions of the amygdala and dorsal hippocampus on the acquisition of conditioned freezing to both the cued CS and to the context in which explicit CS-US pairing occurred”.

(Phillips R. G. and LeDoux, 1992, p.275) Findings: The first experiment was conducted with unoperated rats giving conditioning trials with different magnitude shocks as US, and recording the measured freezing time during both explicit and context periods. It was found that 0.5- mA group as appropriate US parameters. It was also found that “extinction was more rapid with less intense shocks for both CS and pre-CS freezing, and within each US intensity group, extinction to the context was more rapid than extinction to the cued CS” (Phillips R. G. and LeDoux, 1992, p.276) The second experiment was made to record effects of lesions of different brain parts, which were amygdala, dorsal hippocampus, and cortext 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).

Interpretations: 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 an 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. (citation) Finally, as the intensity of the US increases, the organism becomes more sensitive to a wider range of stimulus factors in the environment. The hippocampus may play its role in selecting, which of the many available environmental stimuli are particularly relevant to the immediate situation (Phillips R. G. and LeDoux, 1992, p.284). ) References Phillips R. G. and LeDoux J. E. (1992).

Differential Contribution of Amygdala and Hippocampus to Cued and Contextual Fear Conditioning. Behavioral Neuroscience Vol. 106. No. 2. 274-285