The main reason is the complicated anatomic structure of the nasal cavity and the special physiological location of the olfactory region, which has caused much trouble in direct experiment studies.

这主要是由于鼻腔的复杂结构及嗅区的特殊生理位置，为直接的嗅觉实验研究带来了不少困难。

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Analysis of the brains of the euthanized rats revealed decreased levels of Fos, a protein marker of neuronal activity, in the amygdala region of the brain while the olfactory signals appeared to block fear responses.

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