Depression...

Complete self-absorption.

It's really that simple. Depression basically says "It's all about me." Even though that "me" may be filled with fear, shame, self-hatred, self-loating or self-pity (all of which are self-centered) and may draw sympathy, it's still an act of self-absorption. It's a protective sheath.

Anger turned inwards? Perhaps. But tagging it as 'anger' in some ways provides a justification for it, as if a good reason legitimizes it and provides an excuse for it to continue.

What is the source of this anger? Lack of control? Lack of getting one's way? Helplessness? Futility? Perhaps any or all of these. It's the assertion of power misdirected, i.e. turned inwards.

If someone suffered abuse at an early age and this leads, in later life, to depression, is it not quite simply because power has been taken away?

This isn't necessarily the power to rule the world but to say that this "power" (or, if preferred, energy) would be channeled into having some say in controlling one's destiny. When this power is taken away, the vortex is the source of pain taking this power and absorbing it into a "self" which is a protected, isolated black hole.

This power may leak out in many ways - through artistic endeavor, through anger, through addiction - but it is generally not disciplined. The one in such a state is at the "mercy" of the mystery that lies in this black hole and thus the genius that often arises from it. It is a "mystery" larger then self even though it is self-contained or restricted by one's self. It is the uncontrolled and undisciplined nature of this energy that leads to the highs and lows of genius. The 'self' is at the whim of the extremes.