Us old folk heard that depression was because of low serotonin years ago, and the idea stuck like old gum to the underside of a desk. Yeah, it could be scrapped off, but since we don’t ever see the bottom of the desk, why would we put in the effort. As a side note, that you for you comment as a reminder that I need to see what new treatments to depression do and look into what we have discovered in the last 20 years…