Hi,

The question is still open:

https://www.health.harvard.edu/mind-and-mood/what-causes-depression

http://brainmap.org/pubs/Sacher_JAD_12.pdf

https://www.frontiersin.org/articles/10.3389/fpsyt.2017.00041/full

If you get "definitive" answers, they would depend on who do you ask.

A physiologist will tell you - functional, an anatomist will caution - structural or mixed.

As an anatomist, I can argue that function does not change without some type of structural change, unless an outside biological agent (i.e. bacteria, virus, mold spores) is introduced.

Truth is, it is very difficult to judge, due to the complexity and dynamics of the neuro-endocrine system, of which we still know so little.

Which came first: the chicken or the egg? If you want to get into the minute details and technicalities, functional and structural aspects of any neuropsychological problem are so intertwined they can rarely be -- and often should not be -- separated. In other words, if we think of structure and function as being separate we separate the brain from behavior; we separate genetics and epigenetics from changes to the activity of neurons that result from them.

For example if a gene is faulty or encoded incorrectly for a specific neurotransmitter receptor, we have a structural problem that directly influences the function of the whole neurotransmitter system where that receptor is used. Sometimes the system can compensate rather well and operate relatively normally and you'd never know there was a faulty gene. Other times, it can result in catastrophic problems for the neurotransmitter system and impede function. That impeded function may feed forward into problems with other systems and cause more problems and so on down the chain. When you introduce things like environmental impact on neuronal structure and the resulting functional changes... you end up with an incredibly complicated and inseparable river of signals. A cascade of chemicals being constantly altered by the environment and running on the wetware of our genomes.

In short, your question is a good start, but once you start to delve into the issue, the assumption of a single root cause from either a functional or structural domain my be a false dichotomy with considerable gray area in between.

Thomas Wukitsch Thanks for your inspiring answer! however, there is still a impediment in my mind. We all can feel simply inward, although it is hard to be tested techanically, that in most situations, at the very beginning of a mood activity as a response to an external stimulus, such as something which will inspide desire or angry within us, we actually can with a fairly clear conscious determine to choose to be passionate or be self-controlled. And only when we choose to be the later, the specific kind of mood activity will accordingly arise. In short, does all what we do, what we say and even what we think of not lie under the supervision of conscious? Do we-or to say, the inner spirit of everyone-have no true self at all and all our physical and mental activities are mere a result of a series of responses to verious external information?

Valeria Tananska Thanks!

Junhua Yang Great question! The question of conscious or unconscious control over action and even thought reaches all the way to questions about whether free will truly exists or is a simplification - a construct to help us explain. When I look at the evidence, much of behavior is unconscious: e.g. body language, catching yourself when you are about to trip and fall, quickly withdrawing your hand from a hot bowl, or performing a deeply ingrained habit. From this view, it seems like behavior is an ongoing cycle of environmental interactions influenced by biology and experience. When I experience my own behavior, however, it sometimes does not seem that way, but other times it does. The whole does not appear to be the sum of its parts in some instances, and it clearly does in others. But then again, I am biased merely by being a human.

Repeated bombardment with negative, unpleasant stimuli can influence some very heavily and others not nearly as much. Look into the work of Martin Seligman on learned helplessness. Somewhat ironically, learning about learned helplessness may help!

The question of free will which you delve into later on is one that is difficult to grasp, let alone answer. Personally, I think we must proceed as if free-will is real and be ready to accept that free will may only be a construction of the way we experience our conscious reality.

Thomas Wukitsch Thanks! I will ponder carefully over your answer! Maybe more communications will be made with you in the future. Wishes.

Depression can be endogenous or exogenous. If you all of a sudden experience a death of a beloved one or a crippling disorder you are likely to become depressed at least till you discovered new coping mechanism or work through a heavy grieving process. - Your transmittors change in different ways based on your mood and the biological change results in mood changes per se. This is a vicious circle that needs an exit by the aq wsmwbvg3hhelp of e.g. CBT. Also the inherited vulnerability for mood changes in bipolar disorder has a biological base, already a low suger level may cause mood problems, e.g. irritation. that may be interpreted in the wrong way by the person. I give you examples of event-related depression for more or less vulnerable people: