What are the neurobiological factors related to depression?

Question

While it is agreed that neurotransmitters aren't the primary "cause" of depression, what other factors are a part of this mental illness that focus on the neurobiological aspects of it?

Answer 1

Some experts conceptualize depression as a form of brain damage, to use simple terms. This is called the neurogenic hypothesis of depression.

Depression can be considered a consequence of stress, damaging the brain and weakening its ability to recover on its own. With this model, antidepressants are believed to work because they promote neuronal survival and reduce this stress-induced damage.

In some animal studies, the presence of neurotrophic substances (such as brain-derived neurotrophic factor) in the hippocampus increase in subjects who are chronically exposed to antidepressants.

Answer 2

The main neurobiological factor that most researchers agree upon is neurogenesis in the hippocampus. Several studies (in animals) have found that blocking this causes depression-like behavior and when the neurogenesis returns the depression lifts.

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) system has been strongly implicated in both anxiety and depression, with current wisdom being that depression occurs when the hypothalamus becomes unresponsive to the feedback of cortisol from the adrenal gland.

A less popular theory is one that says depression corresponds to asymmetry in frontal alpha waves between the left and right hemispheres. In this model, relatively high alpha (meaning low actual activity) in the left frontal lobe (or low alpha in the right frontal lobe) is a marker of depression. The right hemisphere is associated with negative emotion in general, so this has some plausibility.