Rhesus monkeys were exposed to lesioning of a specific brain area, and when they woke up they showed a pronounced decrease in their fear responses. the part of the brain that was most likely under investigation in this study was the . amygdala
b. hippocampus
c. basal ganglia
d. medulla oblongata

a. amygdala

Explanation:

According to my research on studies conducted by various neurologists, I can say that based on the information provided within the question the part of the brain that was most likely under investigation in this study was the amygdala. This can be said because the amygdala is the part of the brain that is responsible for emotions, survival instincts (which dictates fear levels), and memory.

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hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.