In his book Musicophilia, Oliver Sacks discusses a case involving a woman named Rachel Y. who lost the ability to process harmony in a car accident. He then explains how this lead to simultanagnosia. He terms this loss of harmony "dysharmonia."
Is dysharmonia a recognized medical condition? My google fu didn't yield anything besides his book. If it is legit, are there any regions of the brain that when damaged induce dysharmonia?
Dysharmonia is not a recognized medical condition, which does not mean that it is not an actual, or real condition. To be a recognized medical condition, there must be more than 1 case report. In medicine, case reports are published in peer-reviewed academic journals. Pubmed (http://www.ncbi.nlm.nih.gov/pubmed) is an indexed compendium of mostly, if not all, peer-reviewed journals and does not bring up any results for dysharmonia. With regard to this case, the person previously had perfect pitch, which is itself rare, and lost a set of musical abilities from the accident. Most individuals who are not highly trained musicians will not notice the loss of musical ability from such an accident if they did not know they had such ability in the first place, which makes it more difficult to have enough individuals to study. In addition, she lost perfect pitch AND the ability to hear in one ear, either of which could have caused the dysharmonia, so it is not clear that dysharmonia is the underlying disorder. There are potentially many different areas of damage that could have caused this. Eg, there are specific areas of brain involved with pitch and with other musical activities. This page goes over some of them: http://www.canadiangeographic.ca/magazine/jf06/alacarte.asp