Music is divine and listening to it can be one of the most rewarding experiences of life. But this art form has also puzzled scientists for long: why do people get hooked on it, when it is not essential for survival like food or sex?

The riddle now seems to have been solved. A team of researchers from Canada’s McGill University has shown that listening to music releases dopamine, a brain chemical associated with pleasure. It’s the same chemical that is released in copious amounts when people gamble, anticipate a cash reward, consume psychoactive drugs or experience sex.

The scientists found that music works on the same reward circuitry in the brain and this explains why people get a “rush” when they listen to music. “This is fascinating because it explains why music has been around for so long,” says Valorie N. Salimpoor, a scientist associated with the study that appeared online in Nature Neuroscience yesterday.

Interestingly, music has been consistently ranked among the top 10 things that people find highly pleasurable. It has existed in every culture throughout recorded history. But what sets it apart from other pleasure-producing stimuli is that it does not deliver any tangible benefit. For instance, in addition to pleasure, food and sex contribute to survival, and hence they are extremely important. Similarly, music does not have direct chemical influences on the brain, unlike drugs or nicotine.

The study proved that an aesthetic stimulus like music could also cause dopamine to be released. “Pleasure from aesthetic stimuli is something that is fairly unique to humans,” says Salimpoor. This is purely intellectual because humans perceive them (aesthetic stimuli) as rewarding, she adds.

Music is a cognitive reward because it involves following a certain sequence of notes. A single note is not pleasurable, but a series of notes arranged in time can be extremely so. This means the listener is cognitively following these notes to the point where some kind of anticipation builds up, of where he or she expects the notes to go. This can lead to either confirmation of the expectation or surprise, both of which may be pleasurable.

The study, led by Robert Zatorre of the Montreal Neurological Institute at the university, also found that the release of dopamine occurs only when people listen in to music they like, not when boring or “neutral” tunes are played.

Despite the established link between listening to music and emotional arousal, it is not clear whether this arousal underlies the pleasurable aspects of music; there is little empirical evidence to suggest that emotional arousal is directly related to music’s rewarding properties.

About three years ago, David Huron, a musicologist at the Ohio State University, came up with a theory of “musical frisson response”, according to which pleasurable music at times evokes a sensation of “chills” and gooseflesh in listeners. This is accompanied big physiological changes, including in the heart beat rate, breathing and body temperature. “These are very good indicators of emotional arousal,” says Salimpoor.

To test the hypothesis that pleasurable music triggers dopamine release, the Canadian scientists subjected eight volunteers to two sophisticated brain tests — positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). While PET can quantify how much dopamine is released in response to a task and in which brain region this occurs, it cannot provide information as to when it is released. fMRI, on the other hand, is capable of detecting when the release has taken place. The volunteers picked their favourite music from different genres.

The idea of using both the instruments simultaneously reaped rich rewards. To the scientists’ surprise, they found that two distinct regions of the brain are involved in the release process. Just before the music is played, the chemical is released from the “caudate”, which is tightly connected to frontal regions of brain that are involved in high-order and complex thinking. Activation of these thinking centres before the music is played proved that music is an intellectual reward, Salimpoor says. “As the peak pleasure approached, the dopamine release was shifted to the ‘nucleuas accumbens’, the reward or pleasure centre of the brain,” she explains.

“Methodologically, the study is a tour-de-force in combining multiple imaging methodologies and a wide range of psychophysiological measurements to study brain response to the anticipation and experience of pleasure,” says Vinod Menon, a professor at the Stanford Institute for Neuro-Innovation & Translational Neurosciences. Menon was one of the first scientists to hypothesise the role of dopamine in pleasurable music listening in 2005.

The scientists say that many eminent composers and performers, even though they do not know the exact mechanism, frequently take advantage of such phenomena, and manipulate emotional arousal by violating expectations in certain ways or by delaying the predicted outcome (for example, by inserting unexpected notes or slowing the tempo). “This then creates a sense of ‘wanting’ in the audience, where they want to hear the resolution of where the notes are going because it is physiologically rewarding for them,” says Salimpoor.

The work may also have some clinical application. The methods developed in this study could be used to investigate the brain chemistry behind anhedonia, the inability to experience pleasure in normal daily activities, says Menon. Anhedonia is a prominent symptom of depression and schizophrenia.

Gamblers and psychoactive drug addicts should perhaps turn to music instead. After all, it’s all about dopamine in the brain.