Nucleus Accumbens

The nucleus accumbens triggers the release of mood effecting hormones, such as dopamine and serotonin (the same hormones whose actions are effected by anti-depressent drugs such as Prozac).  The nucleus accumbens is connected by neuronal fibers to the amygdala (where emotional processing is centered).  Since musical experience activates the amygdala, it also acts upon the nucleus accumbens and hence has mood altering effects.