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I think it's especially interesting that all of these characteristics constitute the broad definition of depression that we hold today.  While we discussed that not every person feels all of these emotional or motor consequences, a large number of people will, at some point, feel almost all of them.  I think this particularly interesting because, as Paul said, there seems to be several causes for this -- but perhaps a 'causal' relationship is not actually how we should approach the situation.  It is probable that, for instance, the emotional 'hopelessness' could cause (see picture) lack of meaning, nothing to draw on to create a story, and so on.  However, I also think it could be an emergent-type feedback system: lots of emotional/motor responses in the brain culminating to form this specific collection of 'consequences.'  However, I've no idea what those intangible feelings/neurons/emotions are that come together to form such a situation.

I do find it interesting that seasonal affective disorder, a subcategory of depression, emits these 'symptoms' listed in the picture only at certain points in time.  Could there be an environmental impact far greater than we have taken into account before?  I think evidence points in this direction for seasonal affective disorder in particular, but perhaps could also hold links to the broader category of depression.