The Danish theologian-philosopher Sören Kierkegaard called despair "the sickness unto death." His description also applies to the severe psychiatric illnesses once labeled melancholia by Freud. These are not the down moods that plague everyone occasionally, but immobilizing and devastating conditions that often cause physical signs and symptoms like loss of appetite and weight, insomnia and slowness of body movement.
Psychiatrists have long suspected that there is a physiological basis for severe depression. They know that thyrotropin-releasing hormone (TRH), a substance released by the hypothalamus at the base of the brain, triggers the production of thyroid-stimulating hormone (TSH); now, they hypothesize that it...
