Hemispheric priming

I've been reading a couple of articles on hemispheric priming.  One, through the BPS Digest, and the other a short section of The Neuroscience of Psychotherapy (I love Kindle editions.  If only they were cheaper).  Beyond the handedness thing, I find hemisphere priming intriguing, although I do have some questions.

Why do frightening faces integrate the hemispheres?  Is the resulting stress response dangerous?  Are temporal abnormalities like those in autism reintegrated with surrounding, and other-hemisphere systems by frightening stimuli?  What are the possible effects of that much cortisol?  Wouldn't the additional stress effects encourage apoptosis?

And what is the limit of stress effects anyway?  These are all important questions to answer, I think.  Particularly the last.  I would expect this to be variable across the general population.  Within autistics particularly, I would expect them to be more prone to stress effects.