This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
In which of the following is blood flow not increased in REM sleep? 
Select and explain. 
A. Primary visual coex, B. Anterior cingulate coex, C. Pons, D. Amygdala
A: Primary visual coex
Answer: A: Primary visual coex 
Explanation: Positron emission tomography (PET) scans of humans in REM sleep show increased activity in the pontine area, amygdala, and anterior cingulate gyrus, but decreased activity in the prefrontal and parietal coex.Activity in visual association areas is increased, but there is a decrease in the primary visual coex. This is consistent with increased emotion and operation of a closed neural system cut off from the areas that relate brain activity to the external world.