"Depression results from a perceived loss of meaning and social resonance, not from a lack of serotonin."

[Rob Northall]

“for the development of depressive disorders, subjective experience in no way merely plays an epiphenomenal role. Rather, the illness originates in a specific perception of the situation, in an “individual act of meaning-ascription” that is not, as an intentional relation to the environment, reducible to neuronal processes. Depression results from a perceived loss of meaning and social resonance, not from a lack of serotonin. Moreover, it is not the objective features of the situation, but their subjective evaluation as insurmountable, which is decisive for the depressive reaction. Consequently, biographically acquired dispositions such as lack of self-worth or self-efficacy become highly influential factors in pathogenesis. Only secondarily do the physiological reactions take on a life of their own as a sustained regulatory dysfunction affecting the entire organism. Granted, in later stages depressive episodes may result from minor events or even from somatic triggers. But even then the organismic dysfunction always remains circularly connected to the patient’s subjective perceptions as well as to their illness-related behaviour in interpersonal relations.

Neurophysiologically (by means of imaging technologies) determinable anomalies in themselves are not more than correlative in character. No such findings could be identified as pathological at all without being related to subjective suffering and intersubjective disturbances.
In the case of obsessive-compulsive disorder (OCD), for instance, hyperactivity of the caudate nucleus provides no indication as to the cause of the disorder. Local activations of the brain’s metabolism only correlatively reflect the function that is being activated; they are only a partial component of the illness. Depressive anxiety disorders are not solely caused by the amygdala, just as OCD is not solely caused by the caudate nucleus, even if these brain regions are implicated in the illnesses. To the extent that neurophysiological changes are to be found, these are correlates, adaptive processes, or biological scars that have emerged in the context of repeated perceptions of situations as dangerous or threatening. Even if neurosystemic developmental impairments in schizophrenia or amygdaloid hyperactivity in posttraumatic stress disorder clearly act as restricting factors, such dysfunctions never become monolinear causes.”

Thomas Fuchs
Are mental illnesses diseases of the brain?
http://books.google.ie/books?id=5-L9Kli6MrkC&pg=PT368&lpg=P...