From a study by Anne J. Blood and Robert J. Zatorre :
We used positron emission tomography to study neural mechanisms underlying intensely pleasant emotional responses to music. Cerebral blood flow changes were measured in response to subject-selected music that elicited the highly pleasurable experience of “shivers-down-the-spine” or “chills.” Subjective reports of chills were accompanied by changes in heart rate, electromyogram, and respiration. As intensity of these chills increased, cerebral blood flow increases and decreases were observed in brain regions thought to be involved in reward/motivation, emotion, and arousal, including ventral striatum, midbrain, amygdala, orbitofrontal cortex, and ventral medial prefrontal cortex. These brain structures are known to be active in response to other euphoria-inducing stimuli, such as food, sex, and drugs of abuse [emphasis added]. This finding links music with biologically relevant, survival-related stimuli via their common recruitment of brain circuitry involved in pleasure and reward.
We know from the experience that classical music decreases crime and drug use. This study shows why; when we listen to music, the reward systems get involved, therefore it may disrupt the addictive behaviours that drive some people to drugs or the “thrill” of crime. In addition, the authors of this study state:
The ability of music to induce such intense pleasure and its putative stimulation of endogenous reward systems suggest that, although music may not be imperative for survival of the human species, it may indeed be of significant benefit to our mental and physical well-being [emphasis added].
In other words, our brains reward us for doing what is good for us!