doi:10.1038/nindia.2013.67 Published online 22 May 2013
For the layman, music is easy to define — it is something that moves him to inexplicable joy or to unfathomable sadness, something that might be a companion while studying or running or even contemplating.
For scientists, however, the science of music has long been a matter of serious wonderment1.
Scientists, including Charles Darwin, have speculated about the need for music or its role in our society and evolution. "As neither the enjoyment, nor the capacity of producing musical notes are faculties of the least use to man in reference to his daily habits of life, they must be ranked among the most mysterious with which he is endowed," Darwin says.
Scientists have also speculated that music, in man, like in birds, could a sexually attractive quality serving as a tool for emotional communication. Many like Michael Gazzaniga believed that creativity underlying artistic pursuits serve a tangible function. Creative processes and cognitive exercises associated with an art form, they say, would have made our ancestors better planners and problem solvers giving them a survival advantage. These and other schools of thought advocate that music composition and improvisation can enhance one's cognitive flexibility and could be an evolutionary mark for physical, mental and emotional fitness.
Scientific data over the past few years has shown that musical training in early years of development induces structural changes in the brain leading to more development in auditory and motor areas.
Music training was shown to improve neural plasticity enabling effective representation of the most meaningful information-bearing sounds. This translated into better language skills, vocabulary and reading ability.
Many like cognitive scientist Steven Pinker have dismissed music as an "auditory cheesecake", quite like our fondness for the desert which is a caloric bombshell triggering diseases like obesity, diabetes. He considers all art forms including music as evolutionary by-products and the pleasures afforded by them to be pleasant coincidences.
This brings us to the last and most recent theoretical framework for the origin of music perception — its similarity to language. Decades ago, celebrated MIT linguist Noam Chomsky proposed the existence of an inherent "knowledge of language" — a set of unconscious principles of grammar and sentence construction universally shared by all humans.
Music, in many ways, is superficially similar to language in that there are deep cultural influences in our perception of sounds, pitches, tones and our ideas of music versus noise. Yet, most people agree to what is musical and what is noise. This implies that, like language, there are inherent limitations to our perception of music. Studies in Rhesus monkeys show that although monkeys do not produce music on their own, they possess musical sensitivity, albeit slightly different from that of humans.
Interestingly, brain imaging shows that while speech is mostly processed in the left half of the brain, music is predominantly perceived in the right. Although these studies suggest that circuits for music and speech do not overlap, others have found several common neural pathways common for both, such as the need for syntax (organizing notes versus organizing words).
Recent evidence also seems to suggest that the right hemisphere is specialized for slower but finer pitch discrimination than the corresponding region on the left. Thus, it is possible that these two abilities are merely two facets of the auditory cortex that were subsequently co-adapted/ co-opted for use in language and music.
This brings us to the second big question — emotionality of music.
While words are emotional because of what they mean to us, they do not make us dance or cry. This is quite unlike music, which is strongly emotive. Music not only triggers psychological changes by influencing our mood, it also affects us physiologically — it makes us tap our limbs, it increases our heart rate and some of our favourite songs send chills down our spine.
Why does this happen? And more importantly how does this happen? These are esoteric but relevant questions that the field of neuroscience is still grappling with.
Valorie Salimpoor and Robert Zatorre in Canada showed that we experience intense pleasure when listening to music because of dopamine activity in the striatum, a part of our "primitive" brain or the limbic system2. They suggest that our perception of music taps into our emotional circuitry and exploits our emotions of expectation, delay, tension, resolution, prediction, surprise and anticipation. We experience similar dopamine release while expecting or anticipating food, sex or psycho-stimulants like cocaine, making them addictive or repeatable.
This sense of pleasure is further amplified when we actually get the reward — like when we finally get to eat! Greater anticipation often leads to greater dopamine release and thus a greater sense of pleasure. Music seems to successfully tap into these two reward phases — anticipation and consummation giving us maximum pleasure.
The anticipation is set off by cues suggesting the onset of a pleasant sound and the reward is obtained when the melody follows an expected pattern. This trick is often used by performers and composers as they manipulate the audience's emotional state by raising expectations, violating them and then ending with the predicted pattern. Music perception also taps into our ability of pattern recognition as we note sound patterns and predict them.
The sense of anticipation however needs to be studied further as it could arise from a cultural or individual familiarity with a style of music or from the existence of an inherent musical structure influenced by genetic and cultural factors.
Last month (April 2013) Salimpoor and Zatorre have extended their previous study and explored some of these underlying questions that make music a rewarding experience3. They evaluated the rewarding experience of music in terms of the amount the listeners were willing to spend to repeat the experience. Since the subjects were spending their own money to purchase the song that they had heard, it was a true estimate of their value for the song. The researchers analyzed brain activity in the listeners as they experienced low, modest or high rewards and found brain areas that correlated with the intensity of these rewards.
They found that the reward value experienced was directly proportional to the activity in two brain regions — dorsal and ventral striatum. Further tracing revealed that a region in the ventral striatum called nucleus accumbens (NAcc) showed robust functional connectivity with regions of the brain's auditory cortex. Although, increased activity in the auditory cortex alone was not sufficient to predict the reward, the strength of their connectivity with the NAcc could predict the music's reward value. Other regions involved in emotional processing and value-guided decision making were also involved in processing the musical stimulus. Their results show that while many brain regions are involved in music processing and evaluation, activity in the striatum alone was proportional to the reward value of the stimulus.
Since the participants in the study were listening to the music clips for the first time and lacked explicit familiarity with the test piece, it is clear that our brains depend on an implicit knowledge of music based on previous exposure. As sound sequences unfold, our expectations of patterns and tonal events rise and shift leading to the firing of dopamine. Thus, listening to music involves continuous and real-time processing of expectancy and evaluation.
Listening to music also initiates sensory-motor interactions coupling the auditory cortex with the premotor and frontal regions leading us to snap those fingers or tap those toes!
They conclude that sound sequences and neutral tones that inherently have no value can interact with our higher levels of cognitive perception and can become salient incentives or pleasures.
Despite these recent studies, our perception of music and its structure remains an enduring puzzle. But increasingly, it seems more and more likely that while our musical abilities may have evolved as a fortuitous by-product, they have cleverly tapped into our emotional circuitry to leave a lasting impression.
By altering our emotional state, music has attained ritualistic significance and has become a tool to manipulate and attain hedonic states.