The Ferber method as far as I can tell is basically emulating the child abandonment episode as done in learned helplessness studies. Learned helplessness, however, appeared to only happen in infant animals up until the animals were weaned off of breast milk. From there, the data suggested the effect was not significant. Learned helplessness could still develop anytime in life but in the studies I mentioned, the act of leaving a newborn mammalian to cry it out had devastating effects on it for the rest of it's life.
Now this of course begs the questions, okay, done in animals, would it happen in humans? We don't know but given the studies were done in several mammals, all of which were of species where the mother spent a significant amount of time rearing the child such as dogs and primates, I do believe this data would carry over to humans.
Data also suggests that cortisol release for about under fifteen minutes is actually beneficial. It's when someone is stressed for too long where it causes the problems. This supports the eustress theory, that stress, within controlled amounts is actually beneficial.
Ultimately, my wife and I decided to do the Ferber method (letting the baby cry it out at night so it can sleep on it's own) because the baby reached the point of eating solid food. Was it right decision? We don't know. We tried to hold off as long as possible but my wife's own mental health was being affected, plus I was concerned she might crash her car due to sleep problems.
I'm not advocating Ferber. For all I know this act is potentially creating learned helplessness in infants, but my point is a lot of data that went into my pro/con debate in my own head was all from a psychology education, not psychiatry. These things do have relevance for a clinician. E.g. my kid's pediatrician was wholeheartedly advocating the Ferber method and I bet she didn't know anything of the learned helplessness studies. In fact this debate is raging on in parenting circles with several citing the learned helplessness data against Ferber.
I typically try to cite the sources of data that I present. Unfortunately it's all from my developmental psychobiology class I took years ago, and that book is at my parents house back in NJ.
Now we get to the part where we learn this in residency and medschool. We learn that depression or excessive anxiety such as that in an anxiety disorder causes prolonged release of cortisol and that is damaging, and that is why medications are extremely helpful, not just improving the patient's mood but also in defending their brain against cortisol-induced damage, particularly to the hippocampus.