Why do we love music?

Why do we love music?

Humans seem to have an innate musicality. That is, the ability to understand and enjoy complex musical patterns appears to be culturally universal. Musicality is expressed very early in development. In this sense, music can be compared to language - because language is the other cognitive way we use sound. But while language is obviously important for communicating sentences or concepts and acquiring such knowledge, this is not the primary function of music. Rather, it is the power of music to convey emotions, moods or affective states of mind that appears to be beneficial to our quality of life.

Which brings us to the question that forms the title of this article: Why do we love music? Essentially, there is no apparent reason why a sequence or pattern of sounds that has no specific propositional meaning should elicit any kind of pleasant response. But music is considered one of our greatest joys. Where does this phenomenon come from?

There are several approaches to this question. A musicologist may have a very different answer than a social scientist. In this article we look at it from the perspective of neuroscience: auditory perception and the reward system. This is the opinion that music derives its power from an interaction between these two systems, the first of which allows us to analyze sound patterns and make predictions about them, and the second that evaluates the results of these predictions and gives positive (or negative) results ) Emotions generated depending on whether the expectation was met, not met or exceeded.

The auditory perception system

It is remarkable that all sounds - a crying baby, thunder, or a waltz - are carried by nothing more than vibrations of molecules in the air. Our rich phenomenological experience with these sounds is the product of a sophisticated perceptual system that captures these vibrations and converts them into what psychologists call internal representations (perceptions, thoughts, memories, emotions, etc.) that are linked to our memories of other sounds and knowledge about the world in general. Part of the process involves extracting relevant acoustic features from the sounds and encoding a pattern.

This process is carried out through operations in three different areas of the brain: brainstem, thalamus and auditory cortex. For example, when plucked, a cello string vibrates at a characteristic frequency based on the physics of its materials and tension; For example, if it were the first string of a conventionally tuned cello, the entire length of the string would vibrate about 65 times in one second, corresponding to the musical note C. Neurons in the aforementioned nuclei and the cortex respond synchronously with a corresponding neuronal oscillation of 65Hz, converting the physical energy into a pattern of neuronal activity that represents the frequency of sound.

Much research suggests that neurons in the auditory cortex, particularly in the right hemisphere of the brain, are important for distinguishing subtle gradations of frequency and generating the psychological sense of pitch. Pitch is fundamental to most music, but it is not enough to simply detect that a pitch has changed; it is important to determine the relationships between pitches within a musical system.

An introductory music theory class would accordingly include a description of musical intervals, the relationship between the frequencies of two tones that determine the patterns that form melodies (when the tones are sequential) and harmonies (when the tones are simultaneous). Importantly, intervals are defined by the relationships between pitches, independent of the pitch values ​​themselves. That is, a minor third is (approximately) defined as the ratio six to five, so that all frequencies in this relationship are perceived as a minor third.

This property, called transposition, allows us to recognize the same song when sung in different keys (if we didn't have this capacity, covers of well-known songs wouldn't work). Several studies have shown that the brain pathways for this type of computation lie outside the auditory cortex proper, in regions associated with it that are also involved in other types of sensory transformations.

A further complication is that sounds immediately disappear from the environment - unlike objects in a visual scene. Because sounds are evanescent, the brain also needs a mechanism to temporarily hold them in memory to calculate pitch ratios and other properties. (This is equally important for language, where a sentence could not otherwise be understood, since every word disappears the moment it is spoken.) This capacity depends on the region of the brain called working memory: roughly that Ability to retain and process information over short periods of time.

Several brain circuits originating from the auditory cortex, particularly the dorsolateral frontal cortex and the posterior areas in the parietal lobe, are important for this ability and therefore essential for musical perception. People with congenital amusia (sometimes called tone deafness) - the inability to understand musical contexts and therefore perceive melodies or other musical structures - have been shown to have reduced connections between auditory areas and frontal areas.

The prediction system

The above description provides a brief and highly simplified insight into some of the mechanisms that allow us to perceive sounds and establish relationships between them. But of course that barely scratches the surface of what has to do with responding to musical sounds. One of the most important aspects of perception that is crucial to music is the ability to anticipate future events based on past experiences.

This is an essential skill for survival because an organism can better prepare an appropriate response to an event if that event can be predicted. In the case of music - and, one thinks, language - there is a rich statistical relationship between sound patterns. Every musical system, like every language, has a syntax, that is, a set of rules about which sounds follow other sounds. The auditory brain is exquisitely sensitive to such regularities and can learn statistical relationships quickly and efficiently, even early in life, through exposure to examples of the system in question (melodies, rhythms, words and sentences). This is how babies get to know the sounds in their environment.

To test the neural substrates of this ability, researchers developed procedures that present a series of sounds that follow usual, expected rules (e.g., a sequence of chords) and then introduce a new element that should either follow or not , based on the context (e.g. a chord with no tone). In this situation, violations of expectancy lead to a characteristic brain reaction that originates in auditory and frontal regions.

Such results show that when we listen to music, we not only encode sound properties and their relationships, but also make predictions about what is coming (otherwise we would not figure out the shaking of the chords). Such predictions are based not only on what was experienced in the moment, but also on knowledge of sound patterns in general, drawn from our entire listening history. Without sufficient exposure to another culture's rule system, predictions are often difficult and that culture's music is difficult to understand. The same principle would apply to the language of another culture.

What about pleasure?

The brain mechanisms outlined very roughly above form the basis for a number of perception and cognitive abilities without which music would not be possible. If we couldn't extract pitch information, hold it in memory, understand pitch relationships, or make predictions, we couldn't have what we call music. But none of this explains why we like music so much. To gain insights into this question, we need to consider an entirely different set of brain structures: the reward system.

Scientists have collected a lot of evidence, both from animal experiments and human studies, to identify the system that signals the presence of a stimulus of value to the organism. An obvious example would be a hungry rat trained to press a lever in response to a cue (e.g. a light turning on) to obtain food. Early studies showed that in this situation, certain neurons located deep in the subcortex, in a structure called the striatum, responded with bursts of dopamine release when food was delivered.

But it soon became clear that these responses did much more than just signal the presence of food, because after some time these neurons stopped responding when the amount of food was constant. That is, when the food was expected, neuronal responses decreased; but if the amount suddenly increased, a powerful dopamine response would return; and if less or no food was provided, the response would actually be inhibited below baseline levels. Thus, this reward system encoded the difference between what was expected and what was actually received, a concept that became known as reward prediction error (where a positive reward prediction error corresponds to a better outcome than expected).

The reward system has been shown to respond to a variety of complex stimuli in humans and animals. Human neuroimaging studies consistently show activity in the striatum and other components of the reward system when people are shown pictures of food, or when they succeed in winning money at gambling, or by playing video games, or when they are shown erotic stimuli. Thus, the reward system is thought to underlie the response to many different types of inputs that are globally beneficial to the survival or well-being of the organism. Food and sex are of course biologically important for survival (of the individual or the species); and money can be viewed as valuable because it can be exchanged for other desired items. Imaging studies have also shown reward system activity for various drugs, including cocaine and amphetamines.

Music and the reward system

So what does music have to do with rats pushing levers or people taking drugs? When music-induced pleasure began to be studied, no one knew whether the same reward system that responds to biologically relevant stimuli would also be affected by a completely abstract stimulus like music. Because music is not necessary for survival, nor is it a medium of exchange like money, nor is it a chemical substance like a drug that can trigger direct neuronal reactions.

Research teams set out to investigate this question using brain imaging techniques that would allow them to measure activity in the striatum during the experience of high levels of music enjoyment. But they immediately encountered a methodological problem: How to measure a subjective response, such as joy, in a rigorous, objective, scientifically sound way? Studying something as complex and potentially uncontrolled as musical emotions presented a particular hurdle. In their initial approach to this question, scientists came up with the idea of ​​studying "chills," the pleasant physical reaction that many people experience people experience when listening to certain musical passages.

The advantage of this approach was that the chills are accompanied by physiological changes (increased heart rate, breathing, skin conductivity, etc.) from which they can derive an objective index about the timing and intensity of maximum pleasure. To implement this idea, they asked each participant to choose their own favorite music that is guaranteed to provide maximum enjoyment. In a series of studies, scientists were able to show that both dorsal and ventral striatum actually respond to moments of peak pleasure induced by music and, with the help of a neurochemically specific radioligand (a radioactive biochemical substance that binds to a relevant molecule), that the Dopamine release in the striatum occurred at these moments.

These studies have changed the understanding of the neurobiology of musical pleasure, but how or why the reward system works remains unanswered. A clue to this question was their observation that there were two phases of the dopamine response: an anticipatory phase that occurs in one subsection of the striatum a few seconds before peak pleasure, and a second response in another subregion at the actual time of pleasure. This finding shows that expectations are as important a source of pleasure as resolutions. Interestingly, music theorists have been noting something similar for many years: that emotional excitement and enjoyment of music comes from creating tension and then leading the listener to expect a resolution of the tension, but then the resolution is sometimes delayed or manipulated in order to to increase the expectation even further.

Using the chill response proved very useful; but one might question whether the reward system's engagement is limited to this experience; Since not everyone gets chills and music can be very enjoyable even without chills, it seemed important to test musical enjoyment without any chills being involved. To do this, the scientists used a paradigm based on neuroeconomics in which people listen to music excerpts and decide how much money they would be willing to spend to buy a recording of it. The amount of money is then an indicator of value and indirectly of pleasure. Using this approach, they also found that the ventral striatum showed increased activity as the value increased.

But a second clue emerged from this study because they also found that the higher the value and response in the striatum, the higher the coupling (measured by correlated brain activity) to the auditory cortex and its associated network: the more listeners liked a particular piece of music (as indexed by their willingness to spend more money), the greater the crosstalk between the striatum and auditory system. This result is important because it links the activity of the perceptual system, as described above, with that of the reward system. So the scientists suggest that the two systems have different functions: the perception mechanism calculates the relationships between the sounds and creates expectations based on these patterns ("I just heard this sound, followed by this sound, so the next one should be X" ); the outcome of the prediction (sound pleasant").

And just as one might expect from the reward prediction model, the reward response is greatest neither when the outcome is exactly as expected (which is boring), nor when the outcome is completely unpredictable (confusing), but when it hits the "sweet spot." , somehow better than expected. This concept, although not yet fully defined, is one that musicians find intuitive: the best music typically neither follows formulaic conventions nor is it too complex to follow, but has the virtue of moderation in its ability to engage the listener to surprise with something new within a predictable framework.

If the musical enjoyment results presented in the preceding sections are roughly correct, this leads to some testable predictions. First, scientists have argued that if music enjoyment arises from interactions between auditory networks and the reward system, such interactions should be interrupted in people who cannot experience music enjoyment. To evaluate this idea, they looked for such individuals and discovered that three to four percent of the population exhibit what we called "specific musical anhedonia." These people have a fairly intact overall hedonic capacity (they enjoy food, sex, social activities, money, even fine art), nor do they have a perceptual disorder such as amusia (tone deafness); they simply do not enjoy or appreciate music, as evidenced by their lack of physiological responses to it.

When the scientists scanned her brain, they discovered that her reward system normally responded to a gamble, but not to music; and the coupling between the auditory and reward systems was essentially absent when listening to music. Thus, as predicted by their model, musical anhedonia arises in the absence of the typical interaction between the two systems.

One could say that musical anhedonia represents a chicken and egg problem: perhaps it is the lack of musical pleasure that leads to a diminished connection between auditory and reward systems, rather than the other way around. To rule out such a possibility, it is important to test a second prediction from their model: if activity in the reward system truly underpins musical pleasure, then we should be able to modulate that pleasure by controlling activity within that system in the manipulate normal brain.

Previous work had shown that it was possible to stimulate or inhibit the reward system by altering dopamine activity in the striatum using a non-invasive brain stimulation technique known as transcranial magnetic stimulation. Scientists recently introduced this technique while people listened to music (their own favorites and some random tracks) and found that listeners felt more pleasure and showed greater physiological responses (skin conductance) to music in the context of arousing stimulation, and showed less enjoyment, even to their own selected music, and showed reduced physiological responses during inhibitory stimulation. This finding provides causal evidence that music enjoyment is directly linked to reward system activity.

We are very pleased that music neuroscience has developed from a fringe field to a solid research area in recent decades, with laboratories in many countries making important contributions and significant advances being published in respected journals. What not long ago seemed like an intractable problem of how music can lead to powerful, effective, and enjoyable responses is now a topic that we understand well enough to have significant insight into and testable hypotheses. It's an exciting time.

Source (English) Robert Zatorre: https://www.dana.org/article/why-do-we-love-music/