These disorders are ubiquitous in all societies and the cause of considerable suffering. The distinctions between depression, in all its forms, and bipolar disease is essential to guiding therapy. These disorders, while manifesting themselves as changes in mental life, are nevertheless, clearly mediated by brain function. They assume great importance for psychiatrists and neurologists but are embedded in the practices of virtually branches of medicine.
Depression is perhaps the cause of more grief and misery than any other single disease to which humankind is subject. This view, expressed by Kline more than 50 years ago, is still shared by almost everyone in the field of mental health and the several forms of depression taken together are the most frequent of all psychiatric illnesses. The Global Burden of Disease Study 2016 affirms this view and estimated that depression is the fourth leading serious illness cause of disability worldwide (after back pain, migraine, hearing loss, and anemia) accounting for approximately 7.5 percent of all years lived with disability. It is also the major contributor to suicide deaths, which number close to 800,000 per year (GBD 2016). In a general hospital, as indicated in the previous chapter, depression accounted for an estimated 50 percent of psychiatric consultations and 12 percent of all admissions.
Although depression has been known for more than 2,000 years (melancholia is described in the writings of Hippocrates), it has been difficult to separate the medical aspects (Kraepelinian concept) from the psychologic reaction (Meyerian concept). In other words, is it basically a biologic derangement or a response to psychosocial stress? A balanced position is both are correct—that is, there are 2 basic forms of depression: exogenous (an apparent cause) and endogenous (with no overt external cause), and that there may be both an interplay between them and biologic susceptibility to either one. However, clinical and physiologic states of depression that do not accord with external circumstances may, when prolonged or severe, constitute an illness. The boundaries between a biological disease and the medicalization of everyday life are therefore necessarily blurred.
In respect to endogenous depression and the related condition of bipolar disease, genetic and neurochemical data cited further on support the kraepelinian view of a disease state. Nevertheless, a lay concept persists, perpetuated by process-oriented psychiatrists, that events in one’s life, either distant or current, underlie all types of depressive illnesses. A consequence of this view is the assumption that an inability to deal with these stresses represents a personal failure of sorts and this in turn may inhibit the acceptance of psychiatric help. It is in this subject of depression that the interplay between our ongoing internal conversation and brain states meets. As noted further on, the difficulties of daily life can entrain the circuits that correspond to depressive feeling and affect. Seeking causality in either direction is complicated and self-referential; for example, functional imaging, ...