The OVLT can sense osmolarity by detecting salt concentration in the bloodstream.

“Special because they lack biological fences around them that other brain areas have. And the those fences or I should say that fence goes by a particular name. And that name is the blood brain barrier or BBB. Most substances that are circulating around in your body do not have access to the brain. In particular, large molecules can't just pass into the brain. The brain is a privileged organ in this sense. However, there are a couple of regions in the brain that have a fence around them, but that fence is weaker.”