How can the aversion response be explained neurologically?
I remembered that Disgust is one of the 6 major emotions and there is quite a lot written about it:


  The neural basis of disgust
  
  The scientific attempts to map specific emotions onto underlying
  neural substrates dates back to the first half of the 20th century.
  However, it was not until the mid-1990s when it was recognized that
  six basic emotions, including disgust, were each related to a specific
  neural structure and therefore considered to be a part of the clinical
  neurosciences.[23] Functional MRI experiments have revealed that the
  anterior insula in the brain is particularly active when experiencing
  disgust, when being exposed to offensive tastes, and when viewing
  facial expressions of disgust.[24] The research has supported that
  there are independent neural systems in the brain, each handling a
  specific basic emotion.[4] Specifically, f-MRI studies have provided
  evidence for the activation of the insula in disgust recognition, as
  well as visceral changes in disgust reactions such as the feeling of
  nausea.[4] The importance of disgust recognition and the visceral
  reaction of "feeling disgusted" is evident when considering the
  survival of organisms, and the evolutionary benefit of avoiding
  contamination.[4] [edit]