I am sure there will be a seriously scientific answer to this question - but more simply - music moves all of us in various ways, even if we fail to understand why. Barber's 'Adagio' is sad music. Why? I have no idea, but play it to an audience, and that's the reaction you will get. Play Tamla Motown records at a party, and people will dance. Why? Still no idea, but the fact is that music affects us in a way that seems almost primeval in its intensity, but if you need the scientific lowdown on chemical changes etc., I'm sorry, but I know that I've listened to some sort of music every day of my life since I've been old enough to have a free will, and I suspect there are many like me. What ever the affect is, it's powerful.