Sociopath - pain = no empathy?

A reader asked this very interesting question:

I learned in a psych class that living things (or mammals, at least), thanks to the magic of mirror neurons, do not distinguish signs of distress in another creature from their own distress. You mention in your one post that you have a very detached stance to pain. What if what we think of as empathy is tied directly to the perception of pain? What if sociopathy is not primarily a lack of empathy, but a greatly altered perception of pain both in oneself and in others? Would it be possible that if an empath's normal neurological responses to pain were tampered with, they would experience less empathy? Could the reverse be true for sociopaths?

I always like these sorts of explanations that somehow tie together different, seemingly unrelated aspects of sociopathy together -- e.g. so insightfully perceptive (enough to be exceptionally manipulative) but lacking empathy?  It's really an odd disorder, with a suite of traits that so consistently present amongst sociopaths and yet seem so scattershot.

One of my favorite unifying theories from a psychologist named Joseph Newman is the idea that sociopathy is largely an attentional disorder, where the sociopath is getting all the right input but is just not paying attention to them in the same way that everyone else is, so they are meaningless to him.

[One of my own pet theories is that a lot of the sociopaths traits (charm, manipulation, lying, promiscuity, chameleonism, compartmentalization, mask wearing, lack of empathy, lack of strong gender, racial, social, sexual or other identity) is largely attributable to a very weak sense of self.  I believe that all personality disorders share a distorted/abnormal sense of self, that that is essentially what makes them a "personality" disorder, and not something else.]  

I also like the one the reader suggested above -- that to the extent sociopaths do not feel things like pain the same way empaths do, the mirror neuron cues are just falling on deaf ears.  But I wonder.  A lot of sociopaths have complained that they have in fact felt something akin to empathy in isolated incidents, particularly if they happen to be feeling something similar at the same moment and happen to recognize that same emotion in others.  This seems to me to be more attentional, but I don't know.