I think we are still in the infancy phase of understanding the brain and how it functions in relationship to music. In some respects it is simply a matter of correctly conceiving the problem. Is music the child of language, or is music the precursor? It will be a while before this is understood. Might it be more fruitful to explore "which came first: the music or the musical brain."
Scientific American Mind has an interesting article in the July/August issue called "Why Music Moves Us" by Karen Schrock. The article is full of speculation about the connection between emotion and music without any real conclusion. But what is interesting is the studies that point to remarkable consistency across cultures when it comes to which qualities of music connect to which emotions.
Some sentences of interest:
"In the late 1990s neuroscientist Isabelle Peretz and her colleagues at the University of Montreal found that Western listeners universally agreed on whether a song using Western tonal elements is happy, sad, scary or peaceful."
"This past April neuroscientist Tom Fritz [...] exposed members of the Mafa ethnic group in Cameroon who had never heard Western music to excerpts of classical piano music. The researchers found that the adults who listened to the excerpts consistently identified them as happy, sad or scary just as Western listeners would."
Similar results were found with autistic children. Infants are more interested in music than in speech. Could it be that music describes to us, abstracts for us the physical characteristics our bodies feel during these emotions?
I've always been of the opinion that music is the beginning of abstraction.