Neurons in the area postrema respond to blood chemicals, consciousness, thoughts, beliefs, and memories.

“And those neurons in the brainstem are triggered by the presence of certain chemicals. And the reason why you don't have any blood brain barrier at that location is because post-trauma has to be there like a crossing guard, making sure that everything that's coming through the blood is okay, and if it even senses just the tiniest bit, that things are off, it's going to trigger that reflex. Now, the really interesting thing is that the neurons and area postrema respond to the chemistry of the blood, but they also will respond to our consciousness, to things that we think and things that we believe and even particular memories.”