Over at the always excellent Not Exactly Rocket Science, Ed Yong summarizes a new investigation into the neural substrate of beauty:

Tomohiro Ishizu and Semir Zeki from University College London watched the brains of 21 volunteers as they looked at 30 paintings and listened to 30 musical excerpts. All the while, they were lying inside an fMRI scanner, a machine that measures blood flow to different parts of the brain and shows which are most active. The recruits rated each piece as “beautiful”, “indifferent” or “ugly”. The scans showed that one part of their brains lit up more strongly when they experienced beautiful images or music than when they experienced ugly or indifferent ones – the medial orbitofrontal cortex or mOFC. Several studies have linked the mOFC to beauty, but this is a sizeable part of the brain with many roles. It’s also involved in our emotions, our feelings of reward and pleasure, and our ability to make decisions. Nonetheless, Ishizu and Zeki found that one specific area, which they call “field A1” consistently lit up when people experienced beauty. The images and music were accompanied by changes in other parts of the brain as well, but only the mOFC reacted to beauty in both forms. And the more beautiful the volunteers found their experiences, the more active their mOFCs were. That is not to say that the buzz of neurons in this area produces feelings of beauty; merely that the two go hand-in-hand.

On the one hand, it's not exactly shocking that beauty can be sourced to the cortex. Where else would it be? Like disgust or delight, beauty is a visceral emotion, a pleasure that Nabokov described as being synonymous with "the the sudden erection of your small dorsal hairs." That beauty can be localized to the mOFC only reminds us that it's part of the pleasure spectrum, since that brain area has consistently been implicated in the recognition of delightful things, from the taste of an expensive wine to the luxurious touch of cashmere.

But why does beauty exist? What's the point of marveling at a Rembrandt self portrait or a Bach fugue? To paraphrase Auden, beauty makes nothing happen. Unlike our more primal indulgences, the pleasure of perceiving beauty doesn't ensure that we consume calories or procreate. Rather, the only thing beauty guarantees is that we'll stare for too long at some lovely looking thing. Museums are not exactly adaptive.

Here's my (extremely speculative) theory: Beauty is a particularly potent and intense form of curiosity. It's a learning signal urging us to keep on paying attention, an emotional reminder that there's something here worth figuring out. Art hijacks this ancient instinct: If we're looking at a Rothko, that twinge of beauty in the mOFC is telling us that this painting isn't just a blob of color; if we're listening to a Beethoven symphony, the feeling of beauty keeps us fixated on the notes, trying to find the underlying pattern; if we're reading a poem, a particularly beautiful line slows down our reading, so that we might pause and figure out what the line actually means. Put another way, beauty is a motivational force that helps modulate conscious awareness. The problem beauty solves is the problem of trying to figure out which sensations are worth making sense of and which ones can be easily ignored.

Let's begin with the neuroscience of curiosity, that weak form of beauty. There's an interesting recent study from the lab of Colin Camerer at Caltech, led by Min Jeong Kang. The experiment itself was straightforward: Nineteen Caltech undergrads were asked 40 trivia questions while in a brain scanner. After reading each question, the subjects were told to silently guess the answer, and to indicate their curiosity about the correct answer. Then, they saw the question presented again, followed by the correct answer.

The first thing the scientists discovered is that curiosity obeys an inverted U-shaped curve, so that we’re most curious when we know a little about a subject (our curiosity has been piqued) but not too much (we’re still uncertain about the answer). This supports the information gap theory of curiosity, which was first developed by George Loewenstein of Carnegie-Mellon in the early 90s. According to Loewenstein, curiosity is rather simple: It comes when we feel a gap “between what we know and what we want to know”. This gap has emotional consequences: it feels like a mental itch. We seek out new knowledge because we that’s how we scratch the itch.

The fMRI data nicely extended this information gap model of curiosity. It turns out that, in the moments after the question was first asked, subjects showed a substantial increase in brain activity in three separate areas: the left caudate, the prefrontal cortex and the parahippocampal gyri. The most interesting finding is the activation of the caudate, which seems to sit at the intersection of new knowledge and positive emotions. (For instance, the caudate has been shown to be activated by various kinds of learning that involve feedback, while it’s also been closely linked to various parts of the dopamine reward pathway.) The lesson is that our desire for more information – the cause of curiosity – begins as a dopaminergic craving, rooted in the same primal pathway that responds to sex, drugs and rock and roll.

I see beauty as a form of curiosity that exists in response to sensation, and not just information. It's what happens when we see something and, even though we can't explain why, want to see more. But here's the interesting bit: the hook of beauty, like the hook of curiosity, is a response to an incompleteness. It's what happens when we sense something missing, when there's a unresolved gap, when a pattern is almost there, but not quite. I'm thinking here of that wise Leonard Cohen line: "There's a crack in everything - that's how the light gets in." Well, a beautiful thing has been cracked in just the right way.

The best way to reveal the link between curiosity and beauty is with music. Why do we perceive certain musical sounds as beautiful? On the one hand, music is a purely abstract art form, devoid of language or explicit ideas. The stories it tells are all subtlety and subtext; there is no content to get curious about. And yet, even though music says little, it still manages to touch us deep, to tittilate some universal dorsal hairs.

We can now begin to understand where these feelings come from, why a mass of vibrating air hurtling through space can trigger such intense perceptions of beauty. Consider this recent paper in Nature Neuroscience by a team of Montreal researchers. Although the study involves plenty of fancy technology, including fMRI and ligand-based positron emission tomography (PET) scanning, the experiment itself was rather straightforward. After screening 217 individuals who responded to advertisements requesting people that experience “chills to instrumental music,” the scientists narrowed down the subject pool to ten. (These were the lucky few who most reliably got chills.) The scientists then asked the subjects to bring in their playlist of favorite songs – virtually every genre was represented, from techno to tango – and played them the music while their brain activity was monitored.

Because the scientists were combining methodologies (PET and fMRI) they were able to obtain a precise portrait of music in the brain. The first thing they discovered (using ligand-based PET) is that beautiful music triggers the release of dopamine in both the dorsal and ventral striatum. This isn’t particularly surprising: these regions have long been associated with the response to pleasurable stimuli. The more interesting finding emerged from a close study of the timing of this response, as the scientists looked to see what was happening in the seconds before the subjects got the chills.

I won’t go into the precise neural correlates – let’s just say that you should thank your right nucleus accumbens the next time you listen to your favorite song – but want to instead focus on an interesting distinction observed in the experiment:

In essence, the scientists found that our favorite moments in the music - those sublimely beautiful bits that give us the chills - were preceeded by a prolonged increase of activity in the caudate, the same brain area involved in curiosity. They call this the “anticipatory phase,” as we await the arrival of our favorite part:

Immediately before the climax of emotional responses there was evidence for relatively greater dopamine activity in the caudate. This subregion of the striatum is interconnected with sensory, motor and associative regions of the brain and has been typically implicated in learning of stimulus-response associations and in mediating the reinforcing qualities of rewarding stimuli such as food.

In other words, the abstract pitches have become a primal reward cue, the cultural equivalent of a bell that makes us drool. Here is their summary:

The anticipatory phase, set off by temporal cues signaling that a potentially pleasurable auditory sequence is coming, can trigger expectations of euphoric emotional states and create a sense of wanting and reward prediction. This reward is entirely abstract and may involve such factors as suspended expectations and a sense of resolution. Indeed, composers and performers 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 tempo) before the resolution to heighten the motivation for completion.

The question, of course, is what all these dopamine neurons in the caudate are up to. What aspects of music are triggering those chills, that visceral perception of beauty? And why are these cells so active fifteen seconds before the acoustic climax? After all, we typically associate surges of dopamine with pleasure, with the processing of actual rewards. And yet, this cluster of cells in the caudate is most active when the melodic pattern is still unresolved, when the musical pattern is still incomplete.

One way to answer these questions is to zoom out, to look at the music and not the neuron. While music can often seem (at least to the outsider) like an intricate pattern of pitches – it’s art at its most mathematical – it turns out that the most important part of every song or symphony is when the patterns break down, when the sound becomes unpredictable. If the music is too obvious, it is annoyingly boring, like an alarm clock. (Numerous studies, after all, have demonstrated that dopamine neurons quickly adapt to predictable rewards. If we know what’s going to happen next, then we don’t get excited.) This is why composers introduce the tonic note in the beginning of the song and then studiously avoid it until the end. They want to make us curious, to create a beautiful gap between what we hear and what we want to hear.

To demonstrate this psychological principle, the musicologist Leonard Meyer, in his classic book Emotion and Meaning in Music (1956), analyzed the 5th movement of Beethoven’s String Quartet in C-sharp minor, Op. 131. Meyer wanted to show how music is defined by its flirtation with – but not submission to – our expectations of order. To prove his point, Meyer dissected fifty measures of Beethoven’s masterpiece, showing how Beethoven begins with the clear statement of a rhythmic and harmonic pattern and then, in an intricate tonal dance, carefully avoids repeating it. What Beethoven does instead is suggest variations of the pattern. He is its evasive shadow. If E major is the tonic, Beethoven will play incomplete versions of the E major chord, always careful to avoid its straight expression. He wants to preserve an element of uncertainty in his music, making our brains exceedingly curious for the one chord he refuses to give us. Beethoven saves that chord for the end.

According to Meyer, it is the suspenseful tension of music (arising out of our unfulfilled expectations) that is the source of the music’s beauty. While earlier theories of music focused on the way a noise can refer to the real world of images and experiences (its “connotative” meaning), Meyer argued that the emotions we find in music come from the unfolding events of the music itself. This “embodied meaning” arises from the patterns the symphony invokes and then ignores, from the ambiguity it creates inside its own form. “For the human mind,” Meyer writes, “such states of doubt and confusion are abhorrent. When confronted with them, the mind attempts to resolve them into clarity and certainty.” And so we wait, expectantly, for the resolution of E major, for Beethoven’s established pattern to be completed. This nervous anticipation, says Meyer, “is the whole raison d’etre of the passage, for its purpose is precisely to delay the cadence in the tonic.” The uncertainty - that crack in the melody - makes the feeling.

What I like about this speculation is that it begins to explain why the feeling of beauty is useful. The aesthetic emotion might have begun as a cognitive signal telling us to keep on looking, because there is a pattern here that we can figure out it. In other words, it's a sort of a metacognitive hunch, a response to complexity that isn't incomprehensible. Although we can't quite decipher this sensation - and it doesn't matter if the sensation is a painting or a symphony - the beauty keeps us from looking away, tickling those dopaminergic neurons and dorsal hairs. Like curiosity, beauty is a motivational force, an emotional reaction not to the perfect or the complete, but to the imperfect and incomplete. We know just enough to know that we want to know more; there is something here, we just don't what. That's why we call it beautiful.

Photo: Courtesy of aclintonb, via Flickr