The sound science of music...

As someone interested in the human mind, it wasn't unusual that I found myself fascinated by the neuroscience of music and our appreciation for it. The search for greater understanding resulted in some very interesting ideas for more blog posts and stories but meanwhile, I did submit my first article to Nature India. It was published there as a feature at the following link. 

http://www.nature.com/nindia/2013/130522/full/nindia.2013.67.html

Like many scientists however, I prefer the unedited, longer version of the same story (as seen below). I hope you will go through both and give me feedback on which one works better for you. 

When Austin Chapman - a twenty three year old filmmaker - heard music for the first time tears rolled down his cheeks even as he tried to hide them. Austin was born profoundly deaf and his hearing aids had never been able to do any justice to the music he heard because they only let him hear the bass and mid tones.  He says of music, “I’ve never understood it. My whole life I’ve seen people make a fool of themselves singing their favorite song or gyrating on the dance floor. That was the hardest thing for me wrap my head around.” But all that changed and the world of sounds attacked him when Austin upgraded to a new pair of Phonak Naida hearing aids. As he sat in the doctor’s office, he first encountered the cacophony of sounds – the hum of the AC, the whir of the computer, the scraping of the shoes and the clacking of the keyboard; they were all new sounds to him. But then, that evening, a group of close friends jump-started his musical education and Austin heard Mozart’s Lacrimosa - for the first time. He realized for the first time what music really was.

Albeit poignant, this is unremarkable to most of us because at one point or another, we have all been moved by music. We have been moved to inexplicable joy or to unfathomable sadness. We have studied to music, run to music or merely contemplated to our favorite sounds. Scientists, on the other hand, have had a much more trying time in their attempts to define music or to even understand its effects on us.

Why music?

Many, including Darwin, have speculated about the need for music and its role in our 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.”  - Charles Darwin

Darwin speculated that music in man, like the colorful plumage in birds, could serve as a sexually attractive quality enabling mate choice. In other words, not unlike today, our ancestral rock stars would have had a large female fan following. He also suggested in passing that music could serve as a tool for emotional communication like between a mother and an infant.

Others like psychologist Michael Gazzaniga from University of California (Santa Barbara) believe that the creativity underlying artistic pursuits (including music perception) served a more tangible function than merely making one more attractive. They posit that the creative processes and the cognitive exercises associated with an art form would have made our ancestors better planners and problem solvers – thus providing them with a survival advantage. They also advocate that music composition and improvisation can enhance one’s cognitive flexibility (by training for perceiving, arranging, rearranging and memorizing the elements of pitch, rhythm, and timbre) and hence, could be an evolutionary tag for physical, mental and emotional fitness. Although this may seem unlikely at first, scientific data over the past few years has indeed shown that musical training in the early years of development (up to age 9) alters the brain structure leading to more development in the auditory and motor areas. Training in music has been seen to improve the plasticity of our neural connections enabling effective encoding of the most meaningful sounds. These effects further translated into better language skills, greater vocabulary and a greater reading ability.

Such beneficial effects however do not establish a cause-and-effect role for music in human evolution. In fact, many like Dr. Steven Pinker, a cognitive scientist from MIT, have dismissed music perception as “auditory cheesecake” – a faculty that exploits other evolutionary-relevant skills such as our ability for language. He considers all art forms including music as evolutionary by-products and the pleasures afforded by them to be pleasant coincidences - quite like our fondness for a cheesecake; which is a caloric bombshell triggering diseases like obesity, diabetes and the rest. If our fondness for something so fatal can survive evolutionary selection – clearly it must be tapping into other more useful traits like a fondness for sugar and fats – which in turn would have been useful to our ancestors.

The language of music and the cross connectivity therein…

The last and most recent theoretical framework for the origins of music perception draws a parallel between music and its similarity to language. Decades ago, linguist Noam Chomsky from MIT, proposed the existence of an inherent “knowledge of language” – a set of unconscious (and potentially inaccessible) principles of grammar and sentence construction that are 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 vs. 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. Attesting to this theory, 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 studies show that while speech processing mostly takes place in the left half of the brain, music is predominantly perceived in the right hemisphere. Although these studies suggest non-overlapping circuits for music and speech, others have found several neural pathways common to both these faculties - such as the need for syntax (organizing notes vs. organizing words).

Although, much of the early evidence is anecdotal and not entirely reliable, recent evidence in the field suggests that our right hemisphere - which is activated by music - is specialized for slower but finer pitch discrimination than the corresponding region on the left. It is speculated that the two hemispheres could have specialized for speed vs. sensitivity. While speech discrimination (in the left hemisphere) requires coarser but faster discrimination of sounds, the right hemisphere may have evolved as a general system for discerning salient sounds from a naturally noisy environment. Thus, it is possible that these two abilities are merely two facets of the auditory cortex that were subsequently co-opted for use in language and music.

The emotional chord…

Music, unlike language, is strongly emotive and Austin experienced it when he heard Lacrimosa for the first time.

Music not only elicits 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 favorite 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.

Drs. Robert Zatorre and Valorie Salimpoor in Canada have been doing some exciting work in this area. Their earlier work in 2012 showed that the intense pleasure experienced when listening to a favorite song is associated with dopamine activity in the striatum – a part of our “primitive” brain or the limbic system. 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 - thereby altering our emotional state.

Similar dopamine mediated euphoria is also anticipated and induced by evolutionarily critical drives like food and sex – making them rewarding and repeatable. Psycho-stimulants like cocaine also cause a similar dopamine rush making them highly addictive. Our brains are also evolutionarily wired such that cues predictive of a future reward lead us to derive pleasure from the mere anticipation of it such as by the pleasant smells of food. This sense of pleasure gets further amplified and reinforced when we actually get the reward. Greater anticipation is seen to lead to a greater dopamine release thereafter and thus a greater sense of pleasure. The longer you wait in spell-bound anticipation or anxiety – the greater the pleasure experienced when the tension is relieved.

Music perception seems to successfully tap into these two reward phases – anticipation and consummation - thereby giving us maximum pleasure. The anticipation is set off by the cues suggesting the onset of a pleasant sound and this very abstract reward is obtained when the melody resolves into the expected pattern. This is of course a common tool used by performers and composers, across genres and cultures, as they manipulate the audience’s emotional state by raising expectations, violating them and then presenting the predicted resolution as a delayed outcome. Music perception also taps into our abilities of pattern recognition as we note sound patterns and predict them. The sense of anticipation however could arise either from a cultural or individual familiarity with a style/piece of music or from the existence of an inherent musical structure, common to us all.

In a more recent report this year, Drs. Zatorre and Salimpoor extended their previous study and explored some of these questions. 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 (and not artificial currency or the project’s funds) 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 identified brain areas that correlated with the intensity of these rewards. Whole brain analysis of oxygenated blood flow during the 30 sec interval when the music was experienced revealed increased activity in the dorsal and ventral striatum, particularly the nucleus accumbens (NAcc) - a region in the ventral striatum. The striatum is a sub-cortical structure i.e. it is buried under the folds of the brain’s cortex and is a region where many cortical signals converge to attain saliency with respect to their impact - pleasure vs. pain. They found that the reward value experienced was directly proportional to the activity in these brain regions.

Further analysis of the brain’s activity showed that the NAcc showed robust functional connectivity with regions of the 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 musical structure based on previous exposure. As sound sequences unfold, our expectations of patterns and tonal events rise and shift leading to the firing of dopaminergic neurons in anticipation and upon successful realization of that prediction. Thus, listening to music involves continuous and real-time processing of expectancy and evaluation as the song unfolds.

These findings show that the rush felt while listening to your favorite song or piece is a complex outcome of many different processes. As the notes unfold, your ears are conveying the sounds to your auditory cortex in the form of electrical impulses. These brain areas then extract the sound relationships and discriminate the organization of sound patterns. These and other regions of the brain contain templates of sounds from past experiences, and based on these, the brain makes predictions about the next note or tone of the melody. These temporal predictions further activate regions of the brain like the NAcc and cause a burst of dopamine, which gives us that heady sense of pleasure. These expectations, pertaining to the harmonic or metrical structure, the timbre, the loudness or the lyrics further establish a new anticipation-prediction cycle. Highly desirable songs are marked by greater connectivity between regions of the auditory cortex with the reward circuits. This also suggests that as we burn through our favorite records, our sense of pleasure will also wane a little, if not altogether, as we become more and more certain of the next tone or note. Our first listening of a melody is different from the rest that follow because our tension and unfamiliarity are much higher.

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. It thus seems that sound sequences and neutral tones that have no inherent value can interact with our higher levels of cognitive perception and can become salient incentives or pleasures.

Despite these recent studies, our implicit perception of music and its structure remains an enduring puzzle. But increasingly, it seems more and more likely that although our musical abilities may have evolved as a fortuitous by-product, they have survived evolution by cleverly tapping into our emotional circuitry. By altering our emotional states, music has attained a ritualistic significance and has become a tool to manipulate and attain hedonic states. It has served many diverse functions in history: by serving as the anthem that cements a group of individuals to serving as a lullaby that bonds the child to its mother. The adoption of music into human societies may have happened by chance but it has cemented its position by altering the very structure of our brains and the fabric of our societies.

It is no wonder then that listening to music for the first time was an intensely emotional experience that drove Austin Chapman on a music-binge from Punk to Rock to Classical trying to identify his favorite sounds. After all, music is as good as that strawberry cheesecake and is much less of a health hazard.

After being transduced into neural impulses by the inner ear, information travels through several way stations in the brainstem and midbrain to reach the auditory cortex. The auditory cortex contains distinct subregions that are important for decoding and representing the various aspects of the complex sound. In turn, information from the auditory cortex interacts with many other brain areas, especially the frontal lobe, for memory formation and interpretation. The orbitofrontal region is one of many involved in emotional evaluation. The motor cortex is involved in sensory–motor feedback circuits, and in controlling the movements needed to produce music using an instrument.          

References

Music, the food of neuroscience? Robert Zatorre; Nature 434, 312-315 (17 March 2005) Published online 16 March 2005

Interactions Between the Nucleus Accumbens and Auditory Cortices Predict Music Reward Value; Science (April 2013) Valorie N. Salimpoor, Iris van den Bosch, Natasa Kovacevic, Anthony Randal McIntosh, Alain Dagher, Robert J. Zatorre

Anatomically distinct dopamine release during anticipation and experience of peak emotion to music; Nature Neuroscience 14, 257–262 (2011) Valorie N Salimpoor, Mitchel Benovoy, Kevin Larcher, Alain Dagher & Robert J Zatorre