Depressive Disorders

A bad week ends. Clinical depression doesn't resolve just because time passes or circumstances improve. Major depressive disorder (MDD) is diagnosed when someone shows at least five symptoms — depressed mood, loss of interest or pleasure, changes in sleep, appetite, or energy, feelings of worthlessness, trouble concentrating, or thoughts of death — nearly every day for at least two weeks, with real impairment in work, relationships, or daily functioning. Persistent depressive disorder (PDD, formerly dysthymia) trades depth for duration: fewer or milder symptoms, but they drag on for at least two years. Picture two mood timelines. MDD looks like a sharp drop into a deep trough that lasts weeks, possibly lifting and recurring in episodes. PDD looks like a shallow line that never climbs back to baseline, a low-grade heaviness stretched across years, sometimes with MDD episodes layered on top.

The cognitive account explains why depression can feel self-sustaining. Aaron Beck's cognitive triad describes three linked negative beliefs: I am worthless (self), nothing will get better (future), and everything is stacked against me (world). Each belief reinforces the others — feeling worthless makes the future look hopeless, a hopeless future makes the world feel hostile, and that hostility confirms worthlessness. This loop filters incoming experience, so even neutral or positive events get reinterpreted as further proof of failure, which is why depression resists being willed away. It is not a lapse in effort or character; the very thinking patterns needed to challenge the loop are compromised by the loop itself.

This connects to Martin Seligman's learned helplessness research, where dogs given inescapable shocks stopped trying to escape even when escape became possible. Depressed humans show a similar pattern: repeated failures or uncontrollable stress teach a sense that nothing one does matters, matching the hopeless, passive outlook of the cognitive triad. Together these models bridge the behavioral and cognitive explanations clinicians use for treatment.