Could anyone tell me if there are any serious neuroscientific mechanisms that have been proposed to explain how feelings of body states take on a positive or negative character (valence)? An example biocomputational approach based on Bayesian inference can be found here. Also related to the Bayesian brain: there is evidence that dopamine communicates prediction error, which has been proposed as a unifying principle for cognition - so I was wondering whether there were any comprehensive theories applying predictive coding to emotion (i.e. valence as prediction error of interoceptive (body) perception). Of course, any theories of valence with similarly broad import would be interesting too.
There is no such universally accepted model. It seems to me that this a specific instance of the hard problem: how can matter have a subjective experience at all?
Of course we know positive experience is associated with dopaminergic action, and often the mechanism has the evolutionary function of surviving and reproducing... and we can argue the same for noxious stimuli - they signal danger in the environment and lead to aversive behaviors.
But this still ignores the phenomenology step, between stimulus and behavior; the nature of the subjective experience. Friston's approach is interesting. I wonder if there is any relationship to be found betweem it and Tononi's model of consciousness (integrated informatiom theory).
With regard to the body perception question, I hope you have read this (doi: 10.1073/pnas.1321664111)