Why Do We Love Music?

. 2018 Nov 1;2018:cer-16-18.Editor’s Note While the human brain is hardwired to feel pleasure for basic survival necessities, such as eating and sex, music—although obviously pleasurable—doesn’t offer the same evolutionary advantages. So why do we respond to patterns of sounds that disappear in an instant? Why do we belt music from the top of our lungs, learn to play instruments, and empty our bank accounts to see Bruce Springsteen on Broadway? Our author offers some valuable insights. Human beings seem to have innate musicality. That is, the capacity to understand and derive pleasure from complex musical patterns appears to be culturally universal.1 Musicality is expressed very early in development.2 In this sense, music may be compared to speech—the other cognitively interesting way that we use sound. But whereas speech is most obviously important for communicating propositions or concepts, obtaining such knowledge, this is not the primary function of music. Rather, it is music’s power to communicate emotions, moods, or affective mental states that seems beneficial to our quality of life. Which brings us to the question that forms the title of this article: why do we love music? On its face, there is no apparent reason why a sequence or pattern of sounds that has no specific propositional meaning should elicit any kind of pleasurable response. Yet music is widely considered amongst our greatest joys.3 Where does this phenomenon come from? There are several approaches to this question. A musicologist might have a very different answer than a social scientist. Since I’m a neuroscientist, I would like to address it from that perspective—recognizing that other perspectives may also offer valuable insights. An advantage of neuroscience is that we can relate our answer to established empirical findings and draw from two especially relevant domains: the neuroscience of auditory perception and of the reward system. To give away the punch line of my article, I believe 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 of which evaluates the outcomes of these predictions and generates positive (or negative) emotions depending on whether the expectation was met, not met, or exceeded.

The Auditory Perception System It’s remarkable to think that all sound—a baby crying, thunder, the strains of a waltz—is carried by nothing more than vibrations of molecules in the air. Our rich phenomenological experience of these sounds is the product of a sophisticated perceptual system that takes these vibrations and transforms them into what psychologists call internal representations (perception, thoughts, memories, emotions, etc.), which can be related to our memories of other sounds and knowledge of the world in general. Part of the process has to do with extracting relevant acoustical features from the sounds and encoding them in the pattern of nerve firings. This process is accomplished by operations happening in three separate brain areas: the brainstem, thalamus, and auditory cortex. A cello string when plucked, for example, will vibrate at a characteristic frequency based on the physics of its materials and its tension; if it is the first string of a conventionally tuned cello, for example, 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 will respond in a synchronized manner with a corresponding neuronal oscillation4 of 65Hz, thus transforming physical energy to a pattern of neural activity representing sound frequency. A great deal of research suggests that neurons in the auditory cortex, especially in the right cerebral hemisphere, are important for distinguishing fine gradations of frequency, creating the psychological sensation of pitch.5 Pitch is fundamental to most music, but it is not sufficient merely to detect that a pitch has changed; it is essential to determine the relationships between pitches within a musical system. An introductory class in music theory would, accordingly, include a description of musical intervals, the ratio between the frequencies of two tones, which determine the patterns that form melodies (when the tones are sequential) and harmonies (when the tones are simultaneous). Importantly, intervals are defined by the relations between pitches independently of the pitch values themselves. That is, a minor third is defined (roughly) as the ratio six to five, so any frequencies in that relation will be perceived as a minor third. This property, known as transposition, is what allows us to recognize the same song when sung in different keys (if we did not have this capacity, covers of familiar songs would not work).

Several studies have indicated that the brain pathways for this kind of computation lie outside the auditory cortex proper, in regions connected to it that are also involved in other kinds of sensory transformations.6 A further complication is that sounds disappear instantly from the environment—unlike, say, objects in a visual scene. Because sounds are evanescent, the brain also needs a mechanism to hold them temporarily in mind, in order to calculate pitch relationships, and other properties. (This is equally important for speech, where a sentence could not otherwise be understood since each word disappears the instant it is spoken.) This capacity depends on the faculty called working memory: roughly, the ability to retain and process information over short time periods. Several brain circuits emanating from the auditory cortex, mainly the dorsolateral frontal cortex and posterior areas in the parietal lobe, are important for this ability, and hence indispensable for musical perception.7,8 People with congenital amusia (sometimes called tone-deafness)—the inability to comprehend musical relationships and hence to perceive melodies or other musical structures—have been found to have reduced connections between auditory areas and frontal regions, and therefore struggle to figure out the relationships between sounds.8The Prediction System The foregoing description gives a brief and highly simplified glimpse of some of the machinery that allows us to perceive tones and determine relationships between them. But, of course, that barely scratches the surface of what’s involved in responding to musical sounds. One of the most important aspects of perception, and one that is critical for music, is the ability to anticipate future events based on past experience.9 This is an essential ability for survival, because an organism can more effectively prepare an appropriate response to an event if that event can be predicted. In the case of music—and, it is thought, of language—there is a rich statistical relationship between patterns of sounds. Every musical system, like every language, has a syntax, that is, a set of rules concerning 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, via exposure to exemplars of the system in question (melodies, rhythms, words, and sentences).

This is how babies learn about sound patterns in their environments.10 To test the neural substrates of this ability, researchers have devised procedures presenting a set of sounds that follows standard, expected rules (e.g., a sequence of chords), and then introducing a new item that either should or should not follow, based on the context (e.g., an out-of-key chord). In this situation, violations of expectancy yield a characteristic brain response that originates in auditory areas and frontal regions.11 Such results reveal that when we listen to music we not only encode sound properties and their relationships, but also make predictions about what’s coming up (otherwise we would not find the out of key chord jarring). Such predictions are based not only on what has just been experienced in the moment, but also on a knowledge of sound patterns in general drawn from our entire listening history. If one lacks sufficient exposure to the rule system of a different culture, appropriate predictions are often difficult, and that culture’s music may be hard to understand. The same principle would apply to another culture’s language.What about Pleasure? The brain mechanisms sketched very roughly above provide the substrates for a number of perceptual and cognitive skills without which, I argue, music would not be possible. If we could not extract pitch information, or hold it in memory, or understand pitch relationships, or make predictions, we could not have what we call music. But none of this explains why we like music so much. For insights into that question, we need to consider a totally different set of brain structures: the reward system. Scientists have accumulated a great deal of evidence, from both animal models and human studies, to identify the system that signals the presence of a stimulus that has value for the organism. An obvious example would be a hungry rat that is trained to press a lever in response to a cue (such as a light coming on) to receive food. Early studies showed that in this situation certain neurons situated deep in the subcortex, in a structure called the striatum, responded with bursts of dopamine release when the food was delivered.12 But it soon became apparent that these responses were doing much more than merely signaling the presence of food, because after a time, these neurons stopped responding if the amount of food was constant.

That is, when the food was expected the neural responses decreased; but if the amount suddenly became larger, a vigorous dopamine response would return; and if less or no food was delivered, the response would actually be inhibited below baseline level.12 Thus, this reward system was encoding the difference between what was expected and what was actually obtained, a concept that became known as reward prediction error (where positive reward prediction error corresponds to a better outcome than was anticipated). The reward system has been shown to be responsive to a wide range of complex stimuli in both humans and animals. Human neuroimaging studies consistently show activity in the striatum and other components of the reward system when people are shown images of food, or allowed to win money in gambling, or by playing video games, or are shown erotic stimuli.13 Thus, the reward system is thought to underlie the response to many different kinds of inputs that are, globally speaking, beneficial to the organism’s survival or well-being. Food and sex are, of course, biologically necessary for survival (of the individual and the species, respectively); and money may be thought of as having value based on the fact that one may exchange it for other desired items. Imaging studies have also shown reward-system activity for various drugs, including cocaine and amphetamines.14Music and the Reward System So what does music have to do with rats pressing levers or people taking drugs? When our group first started to research music-induced pleasure, we did not know whether the same reward system that reacts to biologically relevant stimuli would also be engaged by an entirely abstract stimulus such as music. After all, music is not necessary for survival, nor is it a medium of exchange like money, nor a chemical substance like a drug that can trigger direct neuronal responses. Our team set out to explore this question using brain imaging techniques that would allow us to measure activity in the striatum during the experience of high pleasure from music. But we immediately ran into a methodological problem: how to measure a subjective response, such as pleasure, in a rigorous, objective, scientifically viable manner? The study of something as complex and potentially uncontrolled as musical emotion represented a particular hurdle. In our first approach to this question, we came up with the idea of studying “chills,” the pleasurable physical response that many people experience while listening to certain musical passages.